Behringer FEEDBACK DESTROYER PRO DSP1124P User manual

Users Manual
Version 1.0 February 2001
www.behringer.com
FEEDBACK DESTROYER® PRO DSP1124P
ENGLISH
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FEEDBACK DESTR YER PR DSP1124P
This symbol, wherever it appears, alerts
you to the presence of uninsulated
dangerous voltage inside the enclosure
- voltage that may be sufficient to con-
stitute a risk of shock.
This symbol, wherever it appears, alerts
you to important operating and mainte-
nance instructions in the accompanying
literature. Read the manual.
SAFETY INSTRUCTIONS
CAUTI N: To reduce the risk of electrical shock, do not remove
the cover (or back). No user serviceable parts inside;
refer servicing to qualified personnel.
WARNING: To reduce the risk of fire or electrical shock, do not
expose this appliance to rain or moisture.
DETAILED SAFETY INSTRUCTIONS:
All the safety and operation instructions should be read before the appliance is operated.
Retain Instructions:
The safety and operating instructions should be retained for future reference.
Heed Warnings:
All warnings on the appliance and in the operating instructions should be adhered to.
Follo instructions:
All operation and user instructions should be followed.
Water and Moisture:
The appliance should not be used near water (e.g. near a bathtub, washbowl, kitchen sink, laundry tub, in a wet
basement, or near a swimming pool etc.).
Ventilation:
The appliance should be situated so that its location or position does not interfere with its proper ventilation.
For example, the appliance should not be situated on a bed, sofa rug, or similar surface that may block the
ventilation openings, or placed in a built-in installation, such as a bookcase or cabinet that may impede the
flow of air through the ventilation openings.
Heat:
The appliance should be situated away from heat sources such as radiators, heat registers, stoves, or other
appliance (including amplifiers) that produce heat.
Po er Source:
The appliance should be connected to a power supply only of the type described in the operating instructions
or as marked on the appliance.
Grounding or Polarization:
Precautions should be taken so that the grounding or polarization means of an appliance is not defeated.
Po er-Cord Protection:
Power supply cords should be routed so that they are not likely to be walked on or pinched by items placed
upon or against them, paying particular attention to cords and plugs, convenience receptacles and the point
where they exit from the appliance.
Cleaning:
The appliance should be cleaned only as recommended by the manufacturer.
Non-use Periods:
The power cord of the appliance should be unplugged from the outlet when left unused for a long period of time.
Object and Liquid Entry:
Care should be taken so that objects do not fall and liquids are not spilled into the enclosure through openings.
Damage Requiring Service:
The appliance should be serviced by qualified service personnel when:
- The power supply cord or the plug has been damaged; or
- bjects have fallen, or liquid has been spilled into the appliance; or
- The appliance has been exposed to rain; or
- The appliance does not appear to operate normally or exhibits a marked change in performance; or
- The appliance has been dropped, or the enclosure damaged.
Servicing:
The user should not attempt to service the appliance beyond that is described in the perating Instructions. All
other servicing should be referred to qualified service personnel.
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FEEDBACK DESTR YER PR DSP1124P
FOREWORD
Dear Customer,
Welcome to the team of FEEDBACK DESTR YER PR users and thank you very much for expressing your
confidence in BEHRINGER products by purchasing the DSP1124P. It is one of my most pleasant tasks to
write this letter to you, because it is the culmination of many months of hard work delivered by our engineering
team to reach a very ambitious goal: making an outstanding and extremely flexible device for studios and P.A.
rental companies better still.
The task to design our new FEEDBACKDESTR YERPR certainly meant a great deal of responsibility,
which we assumed by focusing on you, the discerning user and musician. It also meant a lot of work and night
shifts to accomplish this goal. But it was fun, too. Developing a product usually brings a lot of people together,
and what a great feeling it is when everybody who participated in such a project can be proud of what weve
achieved.
It is our philosophy to share our joy with you, because you are the most important member of the BEHRINGER
family. With your highly competent suggestions for new products youve greatly contributed to shaping our
company and making it successful. In return, we guarantee you uncompromising quality (manufactured under
IS 9000 certified management system) as well as excellent technical and audio properties at an extremely
favorable price. All of this will enable you to fully unfold your creativity without being hampered by budget
constraints.
We are often asked how we can make it to produce such high-grade devices at such unbelievably low prices.
The answer is quite simple: its you, our customers! Many satisfied customers means large sales volumes
enabling us to get better conditions of purchase for components, etc. Isnt it only fair to pass this benefit back
to you? Because we know that your success is our success, too!
I would like to thank all people whose help on Project FEEDBACK DESTR YER PR  has made it all
possible. Everybody has made very personal contributions, starting from the designers of the unit via the many
staff members in our company to you, the user of BEHRINGER products.
My friends, its been worth the trouble!
Thank you very much,
Uli Behringer
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FEEDBACK DESTR YER PR DSP1124P
DSP1124P
FEEDBACK DESTROYER® PRO
24-Bit Dual Engine Digital Feedback Destroyer / Parametric EQ Model DSP1124P
sUltra-high performance 2-channel digital Feedback Destroyer / parametric EQ powered by a 24-bit
high-speed DSP
s24-bit A/D and D/A converters with 64/128 times oversampling for ultra-high headroom and resolution
sAutomatically and intelligently searches out and destroys up to 12 frequencies per channel
s24 fully programmable parametric filters that can be set manually or via MIDI
sSet-and-forget default setting enables immediate and super-easy Feedback Destroyer performance
sSingle-Shot mode automatically searches and destroys feedback and locks the filter until you reset it
manually
sAuto mode continuously monitors the mix, resetting programmed filters automatically
sManual mode allows for setting up to 2 x 12 fully parametric filters including frequency, bandwidth and gain
sSingle-Shot, Auto and Manual modes are assignable for each filter
sFree FEEDBACK DESTR YER design software allows for total remote control via PC (download at
www.behringer.com)
sTwo digital processing engines give you independent or coupled functions on left and right channels
sServo-balanced inputs and outputs on gold plated XLR and 1/4" TRS connectors for high signal integrity
sInternal 24-bit processing with professional 46 kHz sampling rate
sFull MIDI capability and user preset memories to store programs for instant recall
sAccurate eight-segment LED level meters simplify level setting for optimum performance
sFuture-proof software-upgradeable architecture
sHigh-quality components and exceptionally rugged construction ensure long life and durability
sInternal power supply design for professional application
sManufactured under IS 9000 certified management system
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TABLE OF CONTENTS
1. INTRODUCTION.....................................................................................................................6
1.1 The design concept ......................................................................................................................... 6
1.2 Before you begin ............................................................................................................................. 6
1.3 Background: How is feedback produced? ........................................................................................7
1.3.1 Background: front of house mix (F H) .................................................................................. 7
1.3.2 Background: monitor mix ...................................................................................................... 7
2. APPLICATIONS .......................................................................................................................8
2.1 Level setting .................................................................................................................................... 8
2.2 Using the FEEDBACK DESTR YER PR in the monitor path ....................................................... 8
2.3 Using the FEEDBACK DESTR YER PR in the F H mix ............................................................ 9
2.4 Using the FEEDBACK DESTR YER PR in a studio environment .............................................. 10
3. A FEW QUICK STEPS TO ELIMINATE FEEDBACK .......................................................... 10
4. CONTROL ELEMENTS ....................................................................................................... 10
5. DSP1124P ARCHITECTURE: PRESETS FILTERS OPERATING
MODES .................................................................................................................................. 13
5.1 Priming the DSP1124P for P.A. and monitor applications ............................................................ 13
6. OPERATING MODES OF THE DSP1124P .......................................................................... 14
6.1 ff mode  F ............................................................................................................................... 14
6.2 Manual filters (PA) / parametric equalizer .................................................................................... 14
6.3 Automatic filters (SI and AU)..................................................................................................... 14
6.4 Locked mode (L ) ...................................................................................................................... 15
7. WORKING WITH PRESETS ................................................................................................. 15
7.1 Recalling Presets .......................................................................................................................... 15
7.2 Selecting the filter operating mode ................................................................................................ 15
7.3 Editing filter parameters ................................................................................................................ 16
7.4 Storing presets .............................................................................................................................. 16
7.5 Restoring the factory presets ........................................................................................................ 16
8. PROBLEMS DO HAVE A CAUSE ... ..................................................................................... 17
9. MIDI CONTROL .................................................................................................................... 17
10.INSTALLATION ..................................................................................................................... 18
10.1Audio connections ........................................................................................................................ 18
10.2 MIDI connections .......................................................................................................................... 20
11.APPENDIX ............................................................................................................................. 20
11.1 Frequency chart ............................................................................................................................ 20
11.2 Preset table .................................................................................................................................. 21
11.3 MIDI implementation ..................................................................................................................... 22
12.SPECIFICATIONS ................................................................................................................. 23
13.WARRANTY ........................................................................................................................... 24
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FEEDBACK DESTR YER PR DSP1124P
1. INTRODUCTION
Thank you very much for expressing your confidence in BEHRINGER products by purchasing the
FEEDBACK DESTR YER PR DSP1124P. With the FEEDBACK DESTR YER PR you have acquired a
highly useful device for the control of sound reinforcement systems, which will enable you to focus your
attention on what is essential: your music. The fully featured DSP1124P not only suppresses feedback but
also incorporates a wealth of additional functions in one single unit. Its 24 separate filters can be edited in all
parameters, and automatically detect and suppress feedback frequencies. With its pro-level internal
processing circuitry, the unit can also be used as a high-end equalizer for stage and studio applications. The
MIDI interface allows for integrating the DSP1124P into any MIDI system, and the open system architecture
enables you to update the system software whenever you want. In short: the DSP1124P will be your reliable
workhorse over many years to come.
+This manual first describes the terminology used, so that you can fully understand the
FEEDBACK DESTROYER PRO and its functions. Please read the manual carefully and keep it
for future reference.
1.1 The design concept
The philosophy behind BEHRINGER products guarantees a no-compromise circuit design and employs the
best choice of components. A 24-bit DSP is used as the heart of the FEEDBACK DESTR YER PR , which
belongs to the best components available owing to its outstanding specifications and excellent sonic
characteristics. What is more, high-quality 24-bit A/D and D/A converters ensure the accurate processing of all
signals. Additionally, the FEEDBACK DESTR YER uses high-quality resistors and capacitors with very tight
tolerances, high-grade switches, and further selected components.
The FEEDBACK DESTR YER PR employs SMD technology (Surface Mounted Device). These subminiature
components known from aerospace technology allow for an extreme packing density and improve the units
reliability even further. Additionally, the DSP1124P was manufactured in compliance with an IS 9000 certified
management system.
1.2 Before you begin
Your FEEDBACK DESTR YER PR was carefully packed in the factory and the packaging was designed to
protect the unit from rough handling. Nevertheless, we recommend that you carefully examine the packaging
and its contents for any signs of physical damage, which may have occurred in transit.
+If the unit is damaged, please do not return it to us, but notify your dealer and the shipping
company immediately, other ise claims for damage or replacement may not be granted.
Shipping claims must be made by the consignee.
The BEHRINGER FEEDBACK DESTR YER PR requires one standard 19" unit of rack space. Please allow
at least an additional 4" depth for the connectors on the back panel.
Be sure that there is enough space around the unit for cooling and please do not place the FEEDBACK
DESTR YER PR on high-temperature devices such as power amplifiers, etc. to avoid overheating.
+Before you connect your FEEDBACK DESTROYER PRO to the mains, please make sure that
your local voltage matches the voltage required by the unit:
The fuse holder on the female mains connector has 3 triangular markings, with two of these triangles opposing
each other. The FEEDBACK DESTR YER PR is set to the operating voltage printed next to these markers
and can be set to another voltage by turning the fuse holder by 180°. CAUTION: This instruction does not
apply to export models exclusively designed, e.g. for 115-V operation!
Please use the enclosed power cord to connect the unit to the mains. The cord complies with all applicable
safety standards.
1. INTR DUCTI N
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+Please note that all units must be grounded properly. For your o n safety, you should never
remove any ground connectors from electrical devices or po er cords or render them
inoperative.
As a standard, the BEHRINGER FEEDBACK DESTR YER PR is equipped with electronically
servo-balanced inputs and outputs. The circuit design features automatic hum and noise reduction for
balanced signals and thus allows for trouble-free operation, even at high operating levels. Externally induced
mains hum, etc. will be effectively suppressed. The automatic servo-function recognizes the presence of
unbalanced connectors and adjusts the nominal level internally to avoid level differences between the input and
output signals (6-dB correction).
The MIDI interfaces IN, UT, and THRU are on standardized DIN connectors. Data are transmitted via
potential-free opto couplers.
1.3 Background: How is feedback produced?
A feedback loop is produced when a microphone signal is reproduced by an amplification system and is
subsequently picked up again (with identical phase) by the microphone. If this happens repeatedly, such a
feedback loop can become ever more persistent.
Fig. 1.1: How a feedback loop is produced
1.3.1 Background: front of house mix (FOH)
There are two main sections in any sound reinforcement system, which are liable to produce feedback: the first
section is the so-called front of house mix (F H), i.e. the public address mix, which is reproduced by one or
several amplifiers plus several loudspeakers directed at the audience.
1.3.2 Background: monitor mix
The monitor mix, which is often derived from the same console, feeds one or several stage-mount monitor
speakers. Unlike F H systems, stage monitors are used to provide the individual musicians with a monitor
signal, because it is often difficult to hear oneself or each other on the stage, which can be due to the high
volume levels produced by the F H systems, or to different volume levels of the stage-mount instruments and
amplifiers. It is therefore not unusual to give each musician his or her own monitor speaker, which is why there
are usually several monitor speakers placed along the stage. This is the only way to provide each musician
with a directed and focused monitor signal. In an ideal situation, each monitor provides a specific mix,
comprising e.g. vocals, drums and keyboards, for each individual musician on the stage.
Unfortunately, it is anything but easy to find perfect positions for the various stage monitors, because the
distance between speaker and microphone must be kept very short, which in turn increases the risk of
feedback.
+In contrast to FOH systems, it is common practice to create t o or even more dedicated
monitor mixes, hich also involves the use of several monitor speakers. Again, this can lead
to increased feedback.
1. INTR DUCTI N
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2. APPLICATIONS
The DSP1124P is used exclusively to eliminate feedback in FOH and monitor mixes.
Before you go on, please note the following two remarks:
+The FEEDBACK DESTROYER PRO is not intended to be connected directly to the microphones!
If this is unavoidable, then e recommend our proven BEHRINGER SHARK DSP110 instead,
hich is equipped ith a dedicated microphone preamplifier.
+No processing device can undo the mistakes made hen placing the microphones! So, hen
you set up your mics, use them according to their directivity and feedback susceptibility
(see chapter 8 PROBLEMS DO HAVE A CAUSE ...).
2.1 Leve setting
Take care to set levels properly on the DSP1124P, so as to successfully employ the FEEDBACK
DESTR YER PR to remove feedback. Use the LED LEVEL METER . Make sure that the top Clip LEDs
flicker only rarely, but never light up all the time.
Low levels deteriorate the dynamics of the music signal, which results in a poor, weak and noisy sound. n the
other hand, excess levels overdriving the converters in the FEEDBACK DESTR YER PR should also be
avoided. Digital distortion is (unlike its analog counterpart) very unpleasant to hear as it does not occur
gradually but abruptly.
2.2 Using the FEEDBACK DESTROYER PRO in the monitor path
Your DSP1124P is equipped with two channels. In Couple mode (see control elements and ), these
two channels are linked. But you can also use them separately, for example, to protect two dedicated monitor
paths against feedback.
Monitor mixes are realized either via the pre-fader Aux Sends on an F H console, or via a (usually stage-
mount) monitor mixer. When using an additional monitor mixer on the stage, you need a so-called splitter to
route the single microphone signals both to the F H console and to the monitor mixer. When using the F H
console for the monitor mix, the stage microphones are connected directly to the console (if necessary, via a
so-called stage box).
In both cases, separate monitor mixes are created for the musicians, which can then be provided from the
console outputs (usually via the Aux Send outputs). wing to its 2-channel design, your FEEDBACK
DESTR YER PR allows you to protect two monitor paths against feedback. To do so, connect the pre-fader
Aux Send outputs on your console to the inputs of the DSP1124 (as shown in fig. 2.1). Then, connect the
inputs of the monitor power amps to the outputs of the FEEDBACK DESTR YER PR (see fig. 2.1).
As already mentioned, monitor paths are particularly susceptible to feedback. When vocal microphones are
not installed in a fixed position, things become even worse, so it really makes sense to protect the monitor
paths against feedback. Another positive side effect of using the DSP1124P in the monitor path is the fact that
you can raise the volume levels considerably.
As you can see, your DSP1124P is a perfect tool to protect two independent monitor paths. But why is that so
important? Because monitoring is a complex task. Usually, each monitor path is used for an independent mix
comprising a variety of signal sources. This is the only way to ensure that each performer on the stage can
hear exactly what he or she wants.
+O ing to its 2-channel design, the DSP1124P is the perfect tool for application in t o separate
monitor paths. Ho ever, if you need to protect four monitors against feedback, e
recommend that you use a second DSP1124P.
+If possible, all monitor paths should be set pre-fader, as this leaves the monitor mix unaffected
from any changes made to the FOH mix.
2. APPLICATI NS
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Fig. 2.1: Using the DSP112 P in the monitor sends
2.3 Using the FEEDBACK DESTROYER PRO in the FOH mix
Since you want to make sure that deliberately produced feedback signals, such as guitar feedback, are not
eliminated, you should try inserting the DSP1124P into those channels that are susceptible to feedback. For
example, you could process a vocal microphone that is liable to produce feedback by connecting the DSP1124P
to the insert points of the respective channel.
Fig. 2.2: Using the DSP112 P for specific mics (connecting the FEEDBACK DESTROYER PRO
in either channel or sub-group inserts)
+When processing a microphone signal ith the DSP1124P and a compressor inserted into the
same channel insert point, the FEEDBACK DESTROYER PRO should al ays be used
pre-compressor: in this ay, the signal is taken at the insert jack, passes the DSP1124P, then
the compressor, and is finally routed back to the insert jack.
Ideally, your mixer has sub-groups with dedicated insert points to connect the DSP1124P! Route all channels
that are susceptible to feedback (e.g. all vocal mics) to one sub-group. While the other signals (e.g. line level
signals, low-level instrumental mics) pass unaffected, all critical microphone channels are monitored by the
DSP1124P.
If your mixer has no sub-group inserts, we recommend that you connect the DSP1124P as follows: connect
the sub-group output to one input on the DSP1124P, and the corresponding output to a free line input of a
mixing console channel or one of the Aux Return inputs on the console. As long as ENGINE L and ENGINE R
are not linked, you would even have the second channel of your FEEDBACK DESTR YER PR free for other
applications (e.g. channel inserts).
2. APPLICATI NS
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2.4 Using the FEEDBACK DESTROYER PRO in a studio environment
With its highly flexible configuration the DSP1124P also delivers good results in a professional studio or home
recording environment, as it provides a maximum of 12 fully parametric equalizers per channel in Parametric
EQ mode. Thus, you can realize any application ranging from slight processing to the total manipulation of
music signals. For example, you can use the DSP1124P as an equalizer for your studio monitors or to
enhance the EQs in your mixing console, as these are often only semi-parametric.
3. A FEW QUICK STEPS TO ELIMINATE FEEDBACK
Irrespective of whether you need the DSP1124P to protect the F H or the monitor mix against feedback, the
following procedure is always the same and should be done before the concert, so as to eliminate basic
feedback problems right before the show begins:
sCheck the setting of the PERATING LEVEL switch on the rear of the unit. For most P.A. systems, this
switch should be set to +4 dB. In doubt, please consult the users manual of your mixing console. Always
make sure that the audio signal levels are set correctly (see control element ).
sSwitch on the unit, and use the J G WHEEL (rotary control) to select preset 1. The preset table (see
table 11.3) lists the various DSP1124P presets available.
sUsing the DSP1124P in the monitor path: Turn up the Aux Send or Mon. controls in the first mic channel,
until the microphone starts to produce feedback. If more than one monitor paths is being used, this
procedure must be done separately for each path. Repeat for each susceptible mic channel.
sUsing the DSP1124P on channel/sub-group inserts: Deliberately induce feedback by setting the channel/
sub-group faders to 0 dB and raising the gain controls for the individual microphones in turn.
In either case, the FEEDBACK DESTR YER PR will suppress feedback as soon as it is producedthe
corresponding LED will stop flashing and stay lit. The various edit options available are described in chapter 7.
But dont let us do the second step before the first:
4. CONTROL ELEMENTS
The BEHRINGER FEEDBACK DESTR YER PR is equipped with ten parameter keys, one J G WHEEL
(rotary control) and a numeric LED DISPLAY. By means of an 8-segment LED meter, each of the two fully
independent channels can be monitored. Each of the 24 filters has one LED assigned to it, which informs about
the status of the filter.
Fig. .1: Display section of the FEEDBACK DESTROYER PRO
1The LED METER is used to monitor the output level. Each channel has eight LEDs assigned to it. When
the Clip LED lights up frequently, this warns you of digital distortion. If the DSP1124P is set to Total
Bypass mode (see ), the level meter reads the input level.
+Please al ays use appropriate level settings, as this is essential for successful feedback
elimination.
2The DSP1124P features 24 filters, i.e. 12 filters per channel. These filters can be monitored conveniently
with the STATUS INDICATOR next to the DISPLAY. 12 LEDs inform you about the status of the filters
on each channel (left/right). A constantly lit LED signals the following conditions:
4. A FEW QUICK STEPS T ELIMINATE FEEDBACK
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s A filter has been set, i.e. it is already suppressing feedback; or:
s A filter is set to Parametric EQ mode (gain ¹ 0 dB).
Cyclically flashing LEDs signal that a filter is searching feedback frequencies in Single-Shot or Auto
mode (see chapters 5 and 6.3). Inactive filters ( F) and filters in Parametric EQ mode (see 6.2), with
a gain setting of 0 dB, are indicated by unlit LEDs.
3The LED DISPLAY consists of a clearly visible, two-digit numeric display. After power-up, it reads the
number of the last preset used. Additionally, the LED-DISPLAY shows the absolute values of the
parameters that are being edited.
4The INDICATORS to the right of the DISPLAY (Hz, kHz, 1/60 and dB) light up when you edit the
associated parameters in Edit mode. For example, when you raise the level of a filter, the dB indicator
lights up.
Fig. .2: Function keys and JOG WHEEL
5With the JOG WHEEL, a continuous rotary control, you can freely edit the selected parameters. Turn
the wheel clockwise to increase the values, or counterclockwise to reduce them.
6With the FILTER SELECT key activated, you can use the J G WHEEL to select one of the 12 filters
per channel. Subsequently, you can edit the filters.
7The FILTER MODE key gives you access to the four operating modes for the individual filters: Off mode
( F), Parametric EQ (PA), Single-Shot mode (SI) and Auto mode (AU). Please read chapter 6
 PERATING M DES F THE DSP1124P.
+Pressing the FILTER MODE and GAIN keys simultaneously allo s you to adjust the sensitivity
of the feedback suppression trigger circuit. The setting range is from -3 through -9 dB and can
be adjusted ith the JOG WHEEL. The default value is -6 dB, as this setting usually delivers the
best results.
8Use the ENGINE L key to select the left audio channel.
9Use the ENGINE R key to select the right audio channel. If you wish to process both channels at the
same time (Couple mode), press both ENGINE keys together. In Couple mode both ENGINE LEDs light
up. Whenever you edit one of the two audio channels and then switch to Couple mode, the parameters
of the active channel will be copied to the other, i.e. if you press ENGINEL before ENGINER, left will be
copied to right.
Items through refer to Parametric EQ mode only (see chapters 5 and 7.3).
10 Press the FREQUENCY key to select the frequency you wish to process. The adjustable frequency
range is from 20 Hz through 20 kHz, which are split up by the DSP1124P into the 31 standard IS
values of a graphic equalizer (see chapter 11.1 in the appendix).
11 The FINE key allows you to fine tune the standard IS frequencies (in 1/60-octave steps), within a
tuning range of 1/3 octave (-9/60 to +10/60).
12 BANDWIDTH determines the filter bandwidth (Q factor) of the selected filter. This adjustable filter quality
ranges from 1/60 octave to 2 octaves (120/60 octave).
4. C NTR L ELEMENTS
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13 The GAIN key sets the desired boost/cut of the selected filter in dB (+16 dB/-48 dB).
14 The IN/OUT key allows for optional bypassing of the parametric filters or all filters. By shortly pressing
the IN/ UT key, only the Parametric EQ filters will be deactivated, and the green LED goes out. Hold
down the key for about two seconds to deactivate all filters. This Total Bypass mode is indicated by the
cyclic flashing of the green LED. Another short IN/ UT key press reactivates all filters. Additionally, the
LED flashes when relevant MIDI data are being received.
+If the control LED of the IN/OUT key flashes, all functions (including all automatic filters used
for feedback suppression) are disabled (Total Bypass). In all other modes, at least the
Single-Shot and Auto filters are active (Bypass).
+Please use the Total Bypass function only ith caution, because the deactivation of the
filters possibly unlocks suppressed feedback.
15 Any modifications made to a preset can be stored with the STORE key, in accordance with the number
shown by the DISPLAY. Ten presets are available on the DSP1124P. Press the IN/ UT and ST RE
keys simultaneously to enter MIDI Setup mode.
16 Use the POWER switch to switch the FEEDBACK DESTR YER PR on or off.
Fig. .3: Rear panel connectors and control elements
17 Use the OPERATING LEVEL switch to change from home recording level (-10 dBV) to studio level
(+4 dBu), and vice versa. The level meters are adapted automatically to the selected nominal level, so
that the FEEDBACK DESTR YER PR will always work in its optimum operating range.
18 These are the balanced INPUTS of the DSP1124P, which are on 1/4" TRS and XLR connectors.
19 The two OUTPUTS of your FEEDBACK DESTR YER PR are also on balanced 1/4" TRS and XLR
connectors.
20 SERIAL NUMBER. Please take the time to fill in and return the warranty card within 14 days after the
date of purchase, so as to benefit from our extended warranty. r use our online registration option
available on the World Wide Web at www.behringer.com.
21 The DSP1124P features a complete set of MIDI functions. In addition to the usual MIDI IN and
MIDI OUT ports, the MIDI THRU allows you to loop through MIDI data.
22 FUSE HOLDER / VOLTAGE SELECTOR. Please make sure that your local voltage matches the
voltage indicated on the unit, before you attempt to connect and operate the unit. Blown fuses may only
be replaced by fuses of the same type and rating. Some models allow for inserting the fuse holder in two
different positions, in order to switch over from 230-V to 115-V operation, and vice versa. Please note
that for 115-V operation outside Europe, you need to use a fuse of a higher rating (see chapter 1.2). Use
the enclosed power cord to connect the unit to the mains.
4. C NTR L ELEMENTS
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5. DSP1124P ARCHITECTURE: PRESETS, FILTERS, OPERATING
MODES
In order to avoid confusion, let us give you a concise description of the DSP1124Ps operating principle, so as
to make the three relevant points clear right from the start. Example: You have set up your P.A. system and
connected all signal sources to the console. The DSP1124P has been inserted into the monitor path (see
fig. 2.1) or in single channel or sub-group inserts (see fig. 2.2); after power-up preset 1 was loaded with the
J G WHEEL. Now, you can start to purposefully produce feedback, as described in chapter 3. Depending on
the room acoustics, various feedback frequencies can occur. What exactly does the DSP1124P do?
As can be seen from table 11.3, each of the ten presets on your DSP1124P comprises 24 separate filters,
which can, however, be set to different operating modes: In our example, the first nine filters of the selected
preset are set to Single-Shot mode (SI, see chapter 6.3). This mode is designed to detect feedback
frequencies at fixed resonance values, and to suppress them consistently. So, these filters cannot be
unlocked (status L  (locked)). Their bandwidth and gain reduction can be adapted if required, however, the
frequency setting remains the same. In our example, the DSP1124P is used to prevent nine fixed frequencies
from making trouble.
The three remaining filters (all set to Auto mode AU, see chapter 6.3) are used to detect and suppress new
feedback frequencies, which can be produced, e.g. when the singer moves around the stage with the vocal mic
in his/her hand. Since the DSP1124P can by no means know whether or not the risk of feedback has been
eliminated (e.g. when the singer moves to another position), the first AU filter of the unit locks to the detected
frequency, while the remaining two AU filters are used to suppress any new trouble frequencies that may
occur. nly when all AU filters have been used, will the first AU filter used (here: 10) be unlocked, so as to be
able to detect new feedback frequencies.
Basically, all active filters (both in AU or SI mode) are represented by flashing LEDs in the STATUS
INDICAT R . When feedback has been detected and is being suppressed, the associated filter LED lights
up constantly. Filters set to Parametric EQ mode (see chapter 6.2) also have constantly lit LEDs.
+Please read the detailed description of all operating modes (chapter 6)!
5.1 Priming the DSP1124P for P.A. and monitor app ications
With the DSP1124P you can improve the protection against feedback even before the show begins, by tuning
in your sound reinforcement system. We already dealt with this in chapter 3. But now its not about using a
preset, but about how to determine in which modes the filters are used: Set some of the filters to Single-Shot
mode (see ).
First, lets take a look at the monitor path: pen all microphone channels, turn up the Aux Send controls on all
channels you wish to route to the monitor mix, then slowly move up the monitor master faders. For the front
mix do as follows: Slowly move up the channel and master faders. In both cases, the first feedback frequencies
can be heard after some time.
Without the FEEDBACK DESTR YER PR you could not increase the volume level of your system any
further. With the DSP1124P, however, you can considerably enhance the system headroom! Let the
Single-Shot filters on the DSP1124P suppress feedback as it occurs. Then cut back the volume to the level
required for the show. In this way, you can be sure that there is enough system headroom should it become
necessary to raise the volume level during the concert.
Experience has shown that musicians want to have the volume of their instrument increased on the monitor as
the concert goes on. With the FEEDBACK DESTR YERPR you can turn up the volume without having to
fear feedback problems. When the show begins you should set several filters to Auto mode, in order to
suppress feedback produced by moving (vocal) microphones. More information on Auto mode can be found
in chapters 5 and 6.3.
5. DSP1124P ARCHITECTURE: PRESETS, FILTERS, PERATING M DES
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. OPERATING MODES OF THE DSP1124P
The individual filters on the BEHRINGER FEEDBACK DESTR YER PR can operate in four different modes
(see ). An additional mode called Locked mode will be described specifically. Basically, each of the
2 x 12 filters on the DSP1124P can be set to any of the four operating modes. To meet more complex
requirements with regard to flexible signal processing, these modes can be combined in a program and stored
in a preset.
6.1 Off mode OF
In Off mode, the corresponding filter is deactivated and can be activated by selecting one of the modes
described below.
6.2 Manua fi ters (PA) / parametric equa izer
To raise or lower specific frequencies in level, you can select these frequencies directly by setting the manual
filters to Parametric EQ mode. Each filter has the functionality of a fully parametric EQ, i.e. you can set the
center frequency (FREQUENCY key ), the bandwidth (BANDWIDTH key ) and the amount of boost/cut
(in dB) using the GAIN key .
6.3 Automatic fi ters (SI and AU)
Automatic filters operate in two modes: Single-Shot (SI) and Auto mode (AU). In order to find a feedback
frequency, the FEEDBACK DESTR YER PR divides the entire frequency band into 1/60 octave steps
(20 Hz to 20 kHz) and determines the respective level of these individual bands. The unit then compares this
value to the level of the entire signal. The difference between these levels determines whether a filter is set or
not. The FEEDBACK DESTR YER PR gives you the unique possibility of adapting this parameter according
to your own needs. You can edit the feedback sensitivity (i.e. the difference value) within a range from -3 to
-9 dB, in 1-dB steps: Simultaneously press the FILTER M DE and GAIN keys, then use the J G WHEEL to
select a value. The standard value for this parameter is -6 dB, which provides for an optimum detection of
feedback in most applications.
Example: During a pure speech transmission, the feedback sensitivity can be lowered to -9 dB. In this way, the
algorithm would recognize and suppress feedback even faster. n the other hand, a higher setting, e.g. -3 dB,
allows you to leave those signals unaffected which you dont want to suppress (e.g. guitar or keyboard
signals).
Filters in Single-Shot mode automatically analyze the music signal to detect feedback frequencies. Having
detected such a frequency, the filter automatically configures its parameters to suppress feedback as
efficiently as possible. As the filter is locked to the detected frequency, this mode is ideally suited to suppress
feedback of constant frequency. Possible applications are fixed-position microphones (e.g. on the drums).
After the filter has adjusted itself automatically, it enters a special Locked mode (see chapter 6.4), which
means that although the frequency remains fixed, the width and depth of the filter are still being adapted to the
feedback frequency, i.e. the width is increased as soon as the feedback frequency begins to shift, and the gain
is cut if feedback prevails. The gain is not reduced to prevent feedback from recurring.
All microphones that are moved during a performance (e.g. vocal mics) very often have varying feedback
frequencies. This type of feedback should be suppressed in Auto mode. As in Single-Shot mode, the filter
automatically selects an ideal setting for feedback suppression. However, in Auto mode the first AU filter set is
unlocked to suppress new feedback. The optimum frequency is selected automatically and the filter is set to
narrow-band mode, so as to influence the music signal as little as possible. If your music contains wanted
feedback elements (e.g. guitar feedback), it is highly probable that these will be suppressed too in Auto mode,
because it is impossible from a physical point of view to distinguish wanted from unwanted feedback.
Please read chapter 2.3 to find some information on how to work around this situation.
6. PERATING M DES F THE DSP1124P
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6.4 Locked mode (LO)
When the DSP1124P detects a feedback frequency in Single-Shot mode (see chapter 6.3), it automatically
enters Locked mode, i.e. the filter locks to the trouble frequency and keeps an eye on it. To unlock such a
filter, you need to switch it back to Single-Shot mode (see and chapter 7.2).
7. WORKING WITH PRESETS
In order to store your favorite settings, the DSP1124P has ten user presets and one default preset. All
operating parameters can be stored, so that your programs are recalled in full detail. wing to state-of-the-art
circuitry, no internal battery is needed, hence the memory contents will not get lost. In the default preset
(DISPLAY: --), which serves as a starting point for your own programs, all filters remain in Parametric EQ
mode, with bandwidth set to 1 octave, frequency to 500 Hz and 0 dB gain.
7.1 Reca ing Presets
The FEEDBACK DESTR YER PR has ten presets, which can be overwritten. After power-up, the unit
restores the last preset used. Use the J G WHEEL to select another preset. The default preset is located
before the first program.
+Please note that the FEEDBACK DESTROYER PRO generally activates the ne ly selected
presets only after about one second, hich is indicated by a dot in the lo er right corner of the
DISPLAY. After loading the data, the FEEDBACK DESTROYER PRO enables the preset and the
dot disappears. This brief interruption of the signal path avoids the direct activation of each
preset, as you scroll through the preset list ith the JOG WHEEL. Thus, the DSP1124P makes
sure that no un anted programs are loaded unintentionally. Additionally, you can rotate
the JOG WHEEL at high speed and still have the time to specifically select the preset of your
choice, instead of any of its neighbors.
7.2 Se ecting the fi ter operating mode
Each filter mode has two letters assigned to it, which appear in the DISPLAY after pressing the FILTER M DE
key. The following display messages are available:
Display Operating mode
OF Off
PA Parametric EQ
AU Auto
SI Single-Shot
LO Locked
Tab. 7.1: FEEDBACK DESTROYER PRO filter operating modes
As already mentioned, the operating mode of a filter can be changed as follows: Press the FILTER SELECT
key and specify the filter number (1 through 12) with the J G WHEEL. Using the two ENGINE keys, you can
select the left (ENGINE L) or right audio channel (ENGINE R), or both at the same time by pressing the two
ENGINE keys simultaneously.
Now, press the FILTER M DE key and select the mode of your choice with the J G WHEEL. The display
message L  (= Locked) informs you that a filter set to Single-Shot mode before is already suppressing
feedback. As described in chapter 6.4, this filter is set to Locked mode automatically. You can unlock such
a filter by switching it back to Single-Shot mode. As soon as a new feedback frequency will be found, the
FEEDBACK DESTR YER PR switches the filter from the old frequency to the new one. If you leave Auto or
Single-Shot mode and enter parametric EQ mode, the filters parameter settings remain unchanged.
7. W RKING WITH PRESETS
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+To avoid inadvertent changing of filter modes, the filter mode selection takes place after
about one second, hich is indicated by a dot in the lo er right corner of the DISPLAY.
+Press the FILTER MODE and GAIN keys at the same time, and use the JOG WHEEL to adjust the
feedback threshold (= feedback sensitivity) ithin a range from -3 to -9dB.
7.3 Editing fi ter parameters
+Remember: Your DSP1124P has ten pre-configured user presets, each comprising 12 filters per
channel. Each individual filter can be selected in any of the four operating modes!
+Ho ever, the Locked mode cannot be selected directly: hen a filter hich as selected as
Single-Shot detects a feedback frequency, the filter is automatically set and locked, i.e.
the filter is locked to the problem frequency and keeps an eye on it.
+In Single-Shot and Auto modes, the filter parameter cannot be edited but only displayed.
Editing can be done in Parametric EQ mode only:
To change filter settings manually, the respective filter must be set to Parametric EQ mode. Press and keep
the FILTER M DE key for about one second. Now, you can adapt the frequency after pressing FREQUENCY.
Depending on the preset frequency, either the Hz or the kHz indicator to the right of the DISPLAY lights up.
For example, when the filter is set to 160 Hz, the numeric DISPLAY will read the value and the Hz indicator
lights up. To raise the frequency to 2,700 Hz, turn the J G WHEEL clockwise until the IS frequency
(2.5 kHz; see Tab. 11.2) next to this value appears in the DISPLAY and the kHz indicator lights up. The FINE
key allows you to fine tune the chosen standard IS frequency within a tuning range of 1/3 octave (in
1/60-octave steps). The mathematical proportion between the displayed value and the absolute frequency, as
well as a guide to find the desired frequency quickly, are listed in the appendix (chapter 11.1  frequency
chart). The bandwidth of the filter (quality) can be adjusted by selecting the BANDWIDTH key. The adjustable
bandwidth ranges from 2 octaves down to 1/60 octave. By pressing the GAIN key, it is possible to set the
desired boost or cut of the selected frequency. A + or - signals that the level is being increased or decreased
respectively.
+Filters in Single-Shot or Auto mode can be transformed into parametric filters ith the same
frequency, quality and 0 dB gain by pressing the FILTER MODE key for about one second. Only
then ill it be possible to edit the filter parameters.
7.4 Storing presets
Whenever you edit a preset, the LED in the ST RE key starts flashing. Basically, all edits in Parametric EQ
mode and the filter deactivation in Off mode can be stored. Filters in Single-Shot or Auto mode adjust and
store their parameters automatically. However, these data will get lost when you switch off the unit. To avoid
that, please write the edited setting to a preset before you switch the DSP1124P off:
Press the ST RE key once, so that the DISPLAY starts flashing. If you wish to preserve the original preset,
use the J G WHEEL to select another preset number, which can be overwritten. Then, press ST RE again to
save your edits to the selected preset. If you wish to overwrite the original preset, simply press the ST RE key
twice after editing, so as to save all edits to the same preset.
7.5 Restoring the factory presets
Press and keep the FILTER SELECT and ST RE keys pressed before you switch on the FEEDBACK
DESTR YER PR . After power-up keep the switches pressed for another second. The preset numbers are
counted up and the presets are reset to their original default values.
7. W RKING WITH PRESETS
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8. PROBLEMS DO HAVE A CAUSE ...
Feedback is one of the major problems encountered in live P.A. applications. In a worst-case scenario every
microphone signal passing an amplifier can cause feedback. Still, theres a lot you can do even before the
show begins:
sPlace the microphones at some distance to the F H and monitor speakers.
sMake sure that the levels of the microphone channels are adjusted correctly (see users manual of your
console).
sUse the microphones according to their polar patterns (e.g. omnidirectional, cardioid, super-cardioid).
sPoor room acoustics should be improved. Tiled walls and floors, which are highly reflective, can be covered
with curtains or carpet.
sUse a graphic equalizer to adapt the overall sound to the room acoustics.
sTo a certain degree, feedback can also be suppressed manually with a graphic EQ.
9. MIDI CONTROL
Use the MIDI key combination to select the MIDI parameters you wish to adjust. To do so, press and keep the
IN/ UT and ST RE keys at the same time. All parameters can be edited with the J G WHEEL and these two
keys. The MIDI menu includes six pages, which you can select by pressing the IN/ UT key (forward) and the
ST RE key (backward) several times.
n the first page, you can select the MIDI channel. The DISPLAY reads a small c (= channel). The
J G WHEEL adjusts a channel from 1 through 16. To switch off the MIDI function, simply select 0 (displayed
as -).
n the second page, you can select MIDI mni mode, i.e. the unit transmits/receives on all 16 MIDI channels.
The DISPLAY reads   (= mni). Use the J G WHEEL to activate (1) or deactivate (0) MIDI mni mode.
The third page allows for the configuration of controller commands. n its right-hand side, the DISPLAY reads
a capital C (= Controller). The J G WHEEL selects one of the five controller modes shown below:
Display Mode
0 No controller data are transmitted
1 Controller data are received but not transmitted
2 Controller data are transmitted but not received
3 Controller data are transmitted and received
4 As 3, with additionally the automatic filter parameters
Tab. 9.1: Controller settings
+When you choose value 4, the FEEDBACK DESTROYER PRO ill send the automatic filter
values in addition to the parameter values.
For details on the controller functions, see Tab. 11.5 in the appendix.
The fourth page gives you access to the Program Changes. The DISPLAY reads a capital P (= Program).
Four modes are available, which can be selected with the J G WHEEL, as follows:
Display Mode
0 No program change data are transmitted
1 Program change data are received but not transmitted
2 Program change data are transmitted but not received
3 Program change data are transmitted and received
Tab. 9.2: Program change settings
8. PR BLEMS D HAVE A CAUSE ...
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The fifth page of the MIDI menu shows the Store Enable flag represented by a capital S in the DISPLAY.
Available values are 0 and 1. If set to 1, the FEEDBACK DESTR YER PR receives controller 18 as a
direct save command, i.e. the current settings will be stored without further confirmation in the preset number
that corresponds to this controller value. If set to 0, the DSP1124P ignores all incoming commands referring
to controller 18.
+ATTENTION! Store Enable mode has been designed to transmit several presets as
conveniently as possible from an external PC to the FEEDBACK DESTROYER PRO. In this
mode, it is possible that stored presets ill be replaced or altered if controller 18 messages are
sent via MIDI! We therefore recommend that you disable this mode as soon as the intended
data transfer has been completed. During po er-up, this mode is automatically disabled
(mode 0).
n the sixth, and presently the last page you can access the System Exclusive functions, which is indicated
by a d (= dump) in the DISPLAY. To the left of this d, you can see a 0 if no sys-ex data can be received or
transmitted. When you enter mode 1, the DSP1124P will be able to receive sys-ex data. In mode 2, the
DSP1124P is ready to dump its entire memory contents with all parameter settings to an external MIDI storage
medium. Start your sequencer software, and press the ST RE key. To load the data back, select mode 1,
and start your sequencer software to restore the settings in your FEEDBACK DESTR YER PR .
If you press the IN/ UT key again on the sixth page, the FEEDBACK DESTR YER PR quits MIDI mode.
You can also use any other key to leave the MIDI setup menu.
The full-featured MIDI implementation of the FEEDBACKDESTR YERPR allows for easily integrating the
unit into any MIDI system.
sMIDI IN
All MIDI data sent to the DSP1124P (sequencer, MIDI foot controller, etc.) are received via the MIDI IN jack. For
example, if you wish to use the DSP1124P as an effects device for your guitar rack, you can connect the
MIDI IN jack to a MIDI foot controller that allows for selecting program presets. If your rack includes another
MIDI effects device, the data sent from the MIDI foot controller can be passed on to that device through the
MIDI THRU port of the FEEDBACK DESTR YER PR .
sMIDI THRU
The MIDI THRU jack is used to loop through incoming MIDI data, i.e. any controller data received at the MIDI IN
of the FEEDBACK DESTR YER PR will be transmitted via the MIDI THRU jack to other MIDI devices/
instruments.
sMIDI UT
The MIDI UT jack allows for transmitting MIDI data that originate from the DSP1124P.
The FEEDBACK DESTR YER Design Editor software enables you to control the DSP1124P from an external
PC. What is more, you can use the FEEDBACK DESTR YER PR to control the editor software, so that both
units communicate with each other. Download the editor free of charge from our web site at www.behringer.com.
10. INSTALLATION
10.1 Audio connections
As a standard, the audio inputs and outputs on the BEHRINGER FEEDBACK DESTR YER PR are fully
balanced. If possible, connect the unit to other devices in a balanced configuration to allow for maximum
interference immunity.
10. INSTALLATI N
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FEEDBACK DESTR YER PR DSP1124P
Fig. 10.1: Different plug types
Fig. 10.2: Wiring an insert cable
+Please ensure that only qualified persons install and operate the FEEDBACK DESTROYER
PRO. During installation and operation the user must have sufficient electrical contact to earth.
Electrostatic charges might affect the operation of the unit.
10. INSTALLATI N
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10.2 MIDI connections
The MIDI connectors found on the rear panel are on internationally standardized 5-pin DIN jacks. You need
dedicated MIDI cables to connect the FEEDBACK DESTR YER PR to other MIDI equipment. Normally,
complete cables will be purchased for this use, but you can also make your own, using a high-quality
two-conductor shielded cables (e.g. microphone cable) and two rugged 180° DIN plugs: pin 2 (center) = shield,
pins 4 and 5 (right and left of pin 2) = internal conductors, pins 1 and 3 (the two outer pins) are not used. MIDI
cables should have a maximum length not exceeding 15 meters.
MIDI IN: Receives MIDI control data. The receive channel is determined in the SETUP menu.
MIDI THRU: Provides an unchanged copy of the signal received at the MIDI IN, for example, to daisy-chain
several FEEDBACK DESTR YER PR s.
MIDI OUT: Transmits MIDI data to a connected computer or other FEEDBACKDESTR YERPR s.
Transmitted are program data as well as status information for signal processing.
11. APPENDIX
11.1 Frequency chart
Display -9/60 -8/60 -6/60 -4/60 -2/60 ISO +2/60 +4/60 +6/60 +8/60 +10/60 Display
20 Hz 20 20,5 21 21,5 22 22,5 20 Hz
25 Hz 22,8 23 23,5 24 24,5 25 25,7 26,3 27 27,6 28,3 25 Hz
32 Hz 28,6 28,9 29,6 30,2 30,9 31,5 32,4 33,2 34,1 34,9 35,8 32 Hz
40 Hz 36,2 36,6 37,5 38,3 39,2 40 41 42 43 44 45 40 Hz
50 Hz45,546474849 50 51 53 54 55 57 50 Hz
63 Hz 57 58 59 60 62 63 65 66 68 70 71,5 63 Hz
80 Hz72,473757778 80 82 84 86 88 90 80 Hz
100 Hz 91 92 94 96 98 100 103 105 108 110 113 100 Hz
125 Hz 114 115 118 120 123 125 129 132 136 139 143 125 Hz
160 Hz 144 146 150 153 157 160 164 168 172 176 180 160 Hz
,20 kHz 182 184 188 192 196 200 205 210 215 220 225 ,20 kHz
,25 kHz 228 230 235 240 245 250 257 263 270 276 283 ,25 kHz
,32 kHz 286 289 296 302 309 315 324 332 341 349 358 ,32 kHz
,40 kHz 362 366 375 383 392 400 410 420 430 440 450 ,40 kHz
,50 kHz 455 460 470 480 490 500 513 526 539 552 565 ,50 kHz
,63 kHz 572 578 591 604 617 630 647 664 681 698 715 ,63 kHz
,80 kHz 724 732 749 766 783 800 820 840 860 880 900 ,80 kHz
1,00 kHz 910 920 940 960 980 1000 1025 1050 1075 1100 1125 1,00 kHz
1,25 kHz 1138 1150 1175 1200 1225 1250 1285 1320 1355 1390 1425 1,25 kHz
1,60 kHz 1443 1460 1495 1530 1565 1600 1640 1680 1720 1760 1800 1,60 kHz
2,0 kHz 1820 1840 1880 1920 1960 2000 2050 2100 2150 2200 2250 2,0 kHz
2,5 kHz 2275 2300 2350 2400 2450 2500 2565 2630 2695 2760 2825 2,5 kHz
3,2 kHz 2858 2890 2955 3020 3085 3150 3235 3320 3405 3490 3575 3,2 kHz
4,0 kHz 3618 3660 3745 3830 3915 4000 4100 4200 4300 4400 4500 4,0 kHz
5,0 kHz 4550 4600 4700 4800 4900 5000 5130 5260 5390 5520 5650 5,0 kHz
6,3 kHz 5715 5780 5910 6040 6170 6300 6470 6640 6810 6980 7150 6,3 kHz
8,0 kHz 7235 7320 7490 7660 7830 8000 8200 8400 8600 8800 9000 8,0 kHz
10,0 kHz 9100 9200 9400 9600 9800 10000 10250 10500 10750 11000 11250 10,0 kHz
12,5 kHz 11375 11500 11750 12000 12250 12500 12850 13200 13550 13900 14250 12,5 kHz
16,0 kHz 14425 14600 14950 15300 15650 16000 16400 16800 17200 17600 18000 16,0 kHz
20 kHz 18200 18400 18800 19200 19600 20000 20 kHz
Tab. 11.1: Frequency chart
In order to maintain a better survey only every second value is registered in the table. The adjustable values do
not exactly fit into a 1/60 octave interval, because also the IS frequencies do not perfectly fit into a physical
1/3 octave interval. Rather a linear approximation is used to specify the values.
Background f1,f2, ... IS frequencies
1 third = 20/60 octave (idealized IS interval)
11.APPENDIX
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