Behringer Tube Ultra-Q T1951 User manual

TUBEULTRA-Q® T1951
www.behringer.com
Version 1.1 November 2001
Users Manual
ENGLISH
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TUBE ULTRA-Q T1951
This s mbol, wherever it appears, alerts
ou to important operating and mainte-
nance instructions in the accompan ing
literature. Read the manual.
SAFETY INSTRUCTIONS
CAUTION: To reduce the risk of electric 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 electric shock, do not
expose this appliance to rain or moisture.
DETAILED SAFETY INSTRUCTIONS:
All the safet and operation instructions should be read before the appliance is operated.
Retain Instructions:
The safet 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, laundr 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 ma block the
ventilation openings, or placed in a built-in installation, such as a bookcase or cabinet that ma impede the
flow of air through the ventilation openings.
Heat:
The appliance should be situated awa from heat sources such as radiators, heat registers, stoves, or other
appliances (including amplifiers) that produce heat.
Po er Source:
The appliance should be connected to a power suppl onl of the t pe 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 suppl cords should be routed so that the are not likel to be walked on or pinched b items placed
upon or against them, pa ing particular attention to cords and plugs, convenience receptacles and the point
where the exit from the appliance.
Cleaning:
The appliance should be cleaned onl as recommended b 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.
Debris and Liquid Entry:
Care should be taken that debris and/or liquids do not enter the enclosure through openings.
Damage Requiring Service:
The appliance should be serviced b qualified service personnel when:
- The power suppl cord or the plug has been damaged; or
- Debris or liquid has entered the appliance; or
- The appliance has been exposed to rain; or
- The appliance does not appear to operate normall 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 be ond that which is described in the operating instruc-
tions. All other servicing should be referred to qualified service personnel.
This s mbol, wherever it appears,
alerts ou to the presence of
uninsulated dangerous voltage inside
the enclosurevoltage that ma be
sufficient to constitute a risk of shock.
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TUBE ULTRA-Q T1951
FOREWORD
Dear Customer,
We thank ou for expressing our confidence in BEHRINGER products b purchasing the BEHRINGER
TUBEULTRA-Q. It is one of m most pleasant tasks to write this preface, as our engineering team has made
it possible to enhance the traditional tube circuitr design (particularl for our VINTAGER series of products),
and adapt it to meet the high sound qualit and d namics requirements of modern, pro-level audio technolog .
The fact that we are still fascinated b antique tube radios and amps as well as the fine and warm tonal
character that we usuall associate with them, are the reasons wh vacuum tubes have kept their ground even
in state-of-the-art circuit topologies used especiall in professional audio technolog or high-end devices. We
are particularl proud that we have found an extremel effective s mbiosis between solid-state and tube
technologies making them affordable to an bod interested in audio technolog . As alwa s, our top-priorit
concern when developing this device was the demanding end user, in other words: ou. It was our major goal
to meet our demands. Sure, it meant a lot of hard work to develop such a product, but the fun has made it all
worthwhile. The shine in the e es of the man interested musicians at the Music Fair 1997, when the saw our
VINTAGER models for the first time, was a lasting incentive driving our development efforts.
It is our philosoph to share our jo with ou, because ou are the most important member of the BEHRINGER
famil . With our highl competent suggestions for new products ouve greatl contributed to shaping our
compan and making it successful. In return, we guarantee ou uncompromising qualit (manufactured under
ISO9000 certified management s stem) as well as excellent technical and audio properties at an extremel
favorable price. All of this will enable ou to full unfold our creativit without being hampered b budget
constraints.
We are often asked how we can make it to produce such high-grade devices at such unbelievabl low prices.
The answer is quite simple: its ou, our customers! Man satisfied customers means large sales volumes
enabling us to get better conditions of purchase for components, etc. Isnt it onl fair to pass this benefit back
to ou? Because we know that our success is our success, too!
I would like to thank all people whose help on Project TUBEULTRA-Q has made it all possible. Ever bod
has made ver personal contributions, starting from the designers of the unit via the man staff members in our
compan to ou, the user of BEHRINGER products.
M friends, its been worth the trouble!
Thank ou ver much,
Uli Behringer
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TUBE ULTRA-Q T1951
T1951
TUBEULTRA-Q®
2 x 4-Band Parametric Tube Equalizer
s4-band parametric stereo equalizer with selected 12AX7 tubes
sULTRA-TUBE circuitr (UTC) adds desired amount of warmth without additional noise
sParallel filter architecture ensures minimal phase shifting
sPrecision state-variable filters with constant-Q characteristic
sUltra low-noise 4580 audio operational amplifiers offer outstanding performance
sSwitchable shelving filter functions remove unwanted frequencies
sEach band can be b passed and is full adjustable from notch filter to broadband equalization
sBroad frequenc band overlapping allows extreme boost/attenuation
sHigh-qualit detented potentiometers and switches with vintage-st le knobs
sCut-in dela to avoid switch-on thumps
sRela -controlled hard b pass with auto b pass function in case of power failure
sServo-balanced gold-plated XLR and 1/4" TRS inputs and outputs
sBEHRINGERs high-performance OT-1 output transformer retrofitable
sHigh-qualit components and exceptionall rugged construction ensure long life even under the most
demanding conditions
sManufactured under ISO9000 certified management s stem
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TUBE ULTRA-Q T1951
TABLE OF CONTENTS
1. INTRODUCTION..................................................................................................................... 6
1.1 The concept .................................................................................................................................... 6
1.2 Before ou get started ..................................................................................................................... 6
1.3 Control elements ............................................................................................................................. 7
2. OPERATION ............................................................................................................................ 9
2.1 Introduction ..................................................................................................................................... 9
2.2 The TUBEULTRA-Q in the signal path ........................................................................................... 9
2.3 Filter settings .................................................................................................................................. 9
2.4 Setting of the tube stage ................................................................................................................ 11
3. APPLICATIONS ..................................................................................................................... 11
3.1 Filtering out unwanted frequencies ................................................................................................. 11
3.2 Shelving filters and Roll Off .......................................................................................................... 12
3.3 Equalizers as creative audio tools ................................................................................................. 12
3.4 The TUBEULTRA-Q as tube interface ........................................................................................... 14
3.5 EQ-ing a P.A. s stem ................................................................................................................... 14
4. TECHNICAL BACKGROUND .............................................................................................. 16
4.1 Function ........................................................................................................................................ 16
4.2 The Constant-Q principle ............................................................................................................. 16
4.3 The concept of parallel filters ......................................................................................................... 16
4.4 On phase shift and time dela ....................................................................................................... 17
4.5 Tubes used in the TUBEULTRA-Q ................................................................................................ 17
4.5.1 Tube histor ........................................................................................................................ 17
4.5.2 Design and functional principle of tubes .............................................................................. 18
4.5.3 Properties of tubes .............................................................................................................. 19
4.5.4 The best of both worlds ....................................................................................................... 19
4.5.5 UTC circuit .......................................................................................................................... 20
4.5.6 Studio applications .............................................................................................................. 20
5. INSTALLATION ..................................................................................................................... 21
5.1 Rack mounting .............................................................................................................................. 21
5.2 Mains voltage ................................................................................................................................21
5.3 Audio connections ........................................................................................................................ 21
5.4 Transformer-balanced outputs (optional) ........................................................................................ 22
6. SPECIFICATIONS ................................................................................................................. 23
7. WARRANTY ........................................................................................................................... 24
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TUBE ULTRA-Q T1951
1. INTRODUCTION
With the BEHRINGER TUBEULTRA-Q T1951 ou have purchased an innovative device. Parametric equalizers
represent the most advanced form of equalization s stems. With the TUBEULTRA-Q ou have purchased an
extremel musical and flexible device. Our ULTRA-Q range of devices has been a hit ever since we introduced
our first model some 5 ears ago. This high-end parametric equalizer is based on man ears of experience
and findings in equalizer technolog and is used throughout the world in renowned studios, sound reinforce-
ment s stems as well as in broadcast and television studios. Improving the legendar ULTRA-Q even further
was a real challenge, and we are proud of our success. The BEHRINGER TUBEULTRA-Q meets highest
requirements in terms of operation, sound, specifications and workmanship.
Even at the conception of the TUBEULTRA-Q it was clear that we had to combine the outstanding technical
specifications of our ULTRA-Q with a warm tube sound. We are therefore proud to be able to present the
TUBE ULTRA-Q, a device featuring our newl developed UTC vacuum tube circuit combined with a no-
compromise approach. The newl developed UTC circuit provides subtle sound enhancement rather than
show effects processing. In particular, digital workstations can be considerabl enhanced in their sound
character. You are free to use the TUBEULTRA-Q before the recording sessions or later when ou mix down
the music ou recorded. You can also use it to brighten up entire MIDI productions or even movie sound
recordings and thus give them their finishing touch.
The philosoph behind BEHRINGER products guarantees a no-compromise circuit design and emplo s the
best choice of components. The op-amps, t pe 4580, used in the TUBEULTRA-Q are chosen for their superior
signal-to-noise ratio, low distortion and linear performance. Additionall , the TUBEULTRA-Quses high qualit
resistors and capacitors with ver tight tolerances, high-grade switches as well other selected components.
The TUBE ULTRA-Q is manufactured under ISO900 certified management s stem.
With the exception of two 12AX7/ECC83 tubes, the TUBEULTRA-Q T1951 is based on SMD technolog
(Surface Mounted Device). These subminiature components known from aerospace applications ensure both
extreme packing densit and greater reliabilit .
+Please keep the manual after reading, in order to use it for future reference.
1.1 The concept
The heart of the TUBEULTRA-Q is an extremel low-noise and transparent sounding state-variable filter. In
combination with the Constant-Q principle, the 4580 op-amp and the newl developed ULTRA-TUBE
technolog , the TUBEULTRA-Q achieves extremel low noise and distortion figures together with an
incredible warm sound. With four full parametric bands, it offers ou trul professional signal processing.
In the TUBE ULTRA-Q, two selected 12AX7 / ECC83 vacuum tubes are used. These triodes are capable of
handling a large d namic range with little microphon . In addition to that their relative ruggedness and above
average life span and ou can see wh its one of the most popular and reliable pre-amp tubes on the market.
These features also ensure ou their availabilit for man ears to come.
Failsafe rela s have been incorporated into the design of the BEHRINGER TUBE ULTRA-Q, which auto-
maticall and silentl b pass the unit in the event of power suppl disconnection or failure. These rela s are
also active at switch-on to isolate the TUBE ULTRA-Q until the power rails have settled, thus preventing the
possibilit of a potentiall damaging switch-on thump.
1.2 Before you get started
Your BEHRINGER TUBE ULTRA-Q was carefull packed in the factor and the packaging was designed to
protect the unit from rough handling. Nevertheless, we recommend that ou carefull examine the packaging
and its contents for an signs of ph sical damage, which ma 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 TUBE ULTRA-Q fits into two standard 19" rack units of space. Please allow at least an
additional 4" / 10 cm depth for the connectors on the back panel.
1. INTRODUCTION
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TUBE ULTRA-Q T1951
Be sure that there is enough space around the unit for cooling and please do not place the TUBE ULTRA-Q on
high temperature devices such as power amplifiers etc. to avoid overheating.
+Before you connect your TUBEULTRA-Q to the mains, please make sure that your local
voltage matches the voltage required by the unit!
The mains connection of the TUBEULTRA-Q is made b using a mains cable and a standard IEC receptacle.
It meets all of the international safet certification requirements. Please make sure that all units have a proper
ground connection.
+Please ensure that only qualified persons install and operate the TUBEULTRA-Q. During
installation and operation the user must have sufficient electrical contact to earth. Electro-
static charges might affect the operation of the TUBEULTRA-Q!
For additional information please refer to chapter 5 INSTALLATION.
As a standard, the audio inputs and outputs on the TUBEULTRA-Q are full balanced. If possible, connect the
unit to other devices in a balanced configuration to allow for maximum interference immunit . The automatic
servo function detects unbalanced connections and compensates the level difference automaticall (6dB
correction).
1.3 Control elements
The BEHRINGER TUBEULTRA-Q has four parametric filters organized in 4 different frequenc bands. A
backlit VU meter shows the input or output level. Each channels comes with a Warmth control, and a tube
window.
Fig. 1.1: Control elements on the front panel
1The INPUT control determines the input level applied to the device and can be set within a range from
-15 to +15dB.
2When the PEAK LED above the INPUT control lights up, it means that a level of at least 18dBu is
present after the input stage. Adjust the INPUT control so that the PEAK LED lights up onl with signal
peaks, make sure that it never lights up all the time. When the PEAK LED is on, there is still some 5dB
of headroom left.
+Please note that extreme boost settings in combination ith a high input level can overload
the unit. In such a case, the input level must be reduced ith the INPUT control.
3The IN/OUT switch is used to enable/disable the entire equalizer section in the audio path. The switch
uses a rela -controlled hard b pass function, i.e. as long as it is not active or if the unit is switched off,
the inputs are directl connected to the outputs. The IN/OUT switch allows for A/B comparisons
between processed and unprocessed signals.
1. INTRODUCTION
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TUBE ULTRA-Q T1951
4The FRE UENCY control selects the filters center frequenc , which can be freel chosen within the
frequenc range of the associated band.
5The LEVEL control determines the amount of level boost/cut. The setting range is from -15 to +15dB.
6The BANDWIDTH control determines the slope or qualit of the filter. Settings from 0.03 (Q = 43) to 2
octaves (Q = 0,67) are possible. A small bandwidth (high Q) means that the onl a small portion of the
total frequenc range will be affected while a wide bandwidth (low Q) means that a large part will be
affected.
7With the SHELF/PEAK switch the two outer bands can be switched from parametric (peaking
response) EQ to low and high pass (shelving EQ) filters respectivel . Use this feature to eliminate
rumble, plop and breathing noises from the bottom end and noise or hiss from the top end. When
switched to PEAK mode the filters operate identical to the other filters.
8The individual IN/OUT switches allow for enabling/disabling specific bands in the audio path. Use this
switch to check the influence of the separate filters and to switch unused filters of for maximum signal
integrit .
Fig. 1.2: Control elements on the front panel
9The WARMTH control determines the amount of harmonics the UTC circuit adds to the signal. This is
the amount of tube sound (WARMTH) that is added.
10 The WARMTH meter displa s the amount of added harmonics. This controls the amount of harmonics,
or tube sound (WARMTH), the UTC circuit adds to the signal.
11 Use the POWER switch to turn the TUBE ULTRA-Q on or off. When switched of the TUBE ULTRA-Q
automaticall switches to a hard b pass mode, the signal is then led directl to the outputs.
13 15
1412
Fig. 1.3: Rear panel elements of the TUBEULTRA-
1. INTRODUCTION
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TUBE ULTRA-Q T1951
12 SERIAL NUMBER. Please complete and return the warrant card within 14 da s of the date of
purchase. Otherwise, ou will lose our right to the extended warrant . Alternativel , ou can register
online at our website under www.behringer.com.
13 FUSE HOLDER / VOLTAGE SELECTION. Before connecting the T1951, confirm that the voltage
displa matches our local mains voltage. When replacing the fuse, ou must alwa s use the same
t pe. In man units the fuse holder can be installed in one of two positions, allowing ou to switch
between 230 V and 115 V. If ou wish to operate a unit outside Europe at 115 V, then a stronger fuse
must be used (see chapter 6 SPECIFICATIONS). The mains connection is made via the IEC
receptacle. An appropriate mains cable is included.
14 AUDIO IN. These are the audio inputs of our TUBEULTRA-Q, available both as balanced 1/4" TRS and
XLR connectors.
15 AUDIO OUT. These are the audio outputs of our TUBEULTRA-Q. Matching 1/4" TRS and XLR
connectors are wired in parallel. The automatic servo function recognizes balanced or unbalanced
connection and automaticall compensates for the difference in level (correction 6dB). The BEHRINGER
OT-1 output transformer is optionall retrofitable.
2. OPERATION
2.1 Introduction
The BEHRINGER TUBE ULTRA-Q gives ou a combination of all technical properties both of parametric
equalizers and of narrow-band notch filters. With its excellent audio qualit and outstanding specifications it is
simpl better than an conventional equalizer. The ULTRA-Q can be used to make up for frequenc response
deficiencies and to creativel process an audio material, thus giving ou undreamed-of equalization flexibilit .
It is a highl efficient and all-purpose tool both in creative audio processing in broadcast and television studios,
in video post-production and on stage. Each of its four bands can be freel adjusted in qualit : from extremel
narrow to broad-band. The TUBEULTRA-Q is superior to graphic equalizers in all respects.
The BEHRINGER TUBE ULTRA-Q uses our newl developed ULTRA-TUBE technolog , a development
resulting from two ears of intensive research work b our engineering team. The ULTRA-TUBE technolog
overcomes the problems related to tube circuitr (see chapter 4) and generates upper harmonics even at low
levels to give our recordings more warmth and power.
2.2 The TUBEULT A-Q in the signal path
The best point to insert the TUBEULTRA-Q in the signal path depends on the task on hand: basicall , it can
be inserted in the main mix insert points of our mixing console, subgroup inserts, subgroup outputs, effects
paths or between signal processor(s) and mixing console/power amp, etc.
Due to its 2-channel architecture, ou can also insert the TUBEULTRA-Q in two independent channels of the
mixing console (if available). This wa the TUBEULTRA-Q acts as a high-qualit and versatile channel EQ.
Depending on the wiring of the inserts on the console, ou either need a special 1/4" stereo insert cable that is
routed to two mono jacks (send & return), or two separate cables for the send and return path. Connect the
insert sends of the subgroups to the inputs on the TUBEULTRA-Q, and the insert returns to the outputs.
You can even connect the two channels of the TUBEULTRA-Q in series to make one equalizer with 8 bands!
Connect the output of channel one with the input of channel two. Set the output of channel one as well as the
INPUT control of channel two at 0dB.
2.3 Filter settings
You ma find that getting to know a dual channel processor like the TUBEULTRA-Q is easier when ou
concentrate on one channel first. If ou have a mixer, connect the TUBEULTRA-Q to the insert of one channel
onl .
Alwa s start off b setting all controls to neutral. All gain controls at 0dB and bandwidth wide. This prevents
wasted time looking for non-existent problems or that settings with a gain higher than 0dB cause problems
2. OPERATION
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TUBE ULTRA-Q T1951
like feedback. In live applications uncontrolled feedback can cause damage to loudspeakers and amplifiers.
B means of the INPUT control ou can adapt the sensitivit of the TUBE ULTRA-Q to the input level. The
sensitivit can be varied within a range of -15 to +15dB. Set the INPUT control so that the PEAK LED lights up
onl rarel , it should never light up constantl . If the LED lights up it means that the level directl after the
INPUT control is exceeding +18dBu, this means that there is still approx. 5dB headroom until the
TUBEULTRA-Q starts clipping.
+Please note that extreme levels can be achieved ith this unit. When a high input level is
combined ith an extreme setting or multiple filters boosting the same frequency range, over-
loading can occur even though the input level as set correctly. This can not be contributed to
a malfunctioning of the unit but is a consequence of the settings that ere chosen. If this
occurs please lo er the input level or choose less extreme settings.
+If extreme equalizer settings are necessary to achieve a usable frequency response, the alarm
bell should start ringing!
The shelving filters
In contrast to graphic equalizers with fixed frequencies and bandwidths ou can freel set all filter parameters,
center frequenc , bandwidth and gain, with a parametric equalizer. The two outer filters of the TUBE ULTRA-Q
can additionall be switched between shelving (SHELF) and bell characteristic (PEAK).
In the setting SHELF the filter resembles a normal tone control on a hifi amplifier, but with the possibilit to alter
the start frequenc and the slope of the filter. The frequenc can be set within a wide range with the
FREQUENCY control. With the BANDWIDTH control the slope can be altered. When the control is turned
counter-clockwise the slope becomes steeper, turning the other wa results in a more gentle slope. The
LEVEL control sets the amount of boost or attenuation. Use the shelving filters to control rumble, plop/
breathing noises and wind or tape hiss. With the freedom to set the frequenc , slope and gain, the
TUBEULTRA-Q can be tailored exactl to our needs giving ou much more flexibilit than an other standard
low-cut switch.
The parametric filters
When the first and the last filters are set to PEAK, the are identical to the two other filters. In that case the
filters have a peaking response or a bell curve. Start b boosting a fairl broad frequenc band to locate the
frequenc band ou want to adjust. It is easier to locate problem frequencies b boosting them first. When the
problem frequenc is located ou can adjust the bandwidth to isolate the correct range. Now ou can cut or
boost this range to suit our needs. The filters are set up in such a wa that the cover the entire spectrum from
20Hz to 20 kHz, while overlapping each other over a wide range. After finding the right setting ou can tweak
the setting of each band to achieve maximum results.
During operation ou can switch on and off the individual bands to make an A/B comparison between the
equalizer effect and the unprocessed signal. Due to the complex and partl difficult settings of parametric
equalizers such a facilit is indispensable. Still, most parametric EQs have no band-specific in/out switches
which makes it difficult to keep track of what the various switches and controls do.
Adjusting the overall level
It is possible that ou have to correct the overall level after setting the equalizer. It is possible that the effect of
the filters result in a higher or lower level than the original signal. Use the INPUT control to adjust the total level.
You can compare the processed and unprocessed level with the help of the IN/OUT switch.
+Please note that the IN/OUT performs a hard are bypass. The input signal is fed directly to the
output. The INPUT control has no influence.
2. OPERATION
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TUBE ULTRA-Q T1951
Fig. 2.1: Various filter qualities
2.4 Setting of the tube stage
With the settings ou have achieved so far a considerable sound improvement can be made. You ma not
know this, but ou have alread benefitted from the tube stage of the TUBEULTRA-Q. Even when the WARMTH
control is turned full counter-clockwise, subtle and hardl noticeable warmth and musicalit is added to the
signal. You can now drasticall increase the effect b turning up the WARMTH control.
With the tube stage featured in the BEHRINGER TUBEULTRA-Q ou can add the t pical tube sound with the
WARMTH control.Increasing amounts of upper harmonics generated b the new UTC circuitr are then added
to the signal. This leads to more musical and transparent hights which combine perfectl with the enhancer/
exciter effect, which can perhaps even be reduced a little in favor of the warm tube sound. You can monitor the
amount of WARMTH that is added with a glance at the WARMTH meter.
3. APPLICATIONS
3.1 Filtering out unwanted frequencies
One of the most important tasks of the TUBEULTRA-Q is the notching out of problem frequencies. With
notching or peaking we describe the specific attenuation of single frequencies or frequenc bands. A notch
filter produces an effect that is the opposite of a band-pass filter. Specific frequencies or ranges can be
targeted like hum, rattle or feedback frequencies. Resonance in a room or microphone can be eliminated
effectivel .
Fig. 3.1: Typical notch function
3. APPLICATIONS
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TUBE ULTRA-Q T1951
Because of the wide overlap possibilit of the different filters, the effect of two filters can be added together if so
desired. This wa an even greater attenuation or boost can be achieved.
When notching out frequencies tr to make the band as small as possible. Alwa s as little as possible but as
much as needed.
3.2 Shelving filters and  oll Off
Switching one or two of the outer filters to SHELF enables ou to adapt or limit the entire frequenc response.
With the LEVEL control ou can set the degrees of boost or attenuation, with the BANDWIDTH control the
slope and with FREQUENCY control the frequenc from which the slope starts.
Practice has shown how important this feature is, as most acoustic problems are encountered in the extreme
low and high frequenc ranges. T pical frequenc response, hum or feedback problems must be handled
differentl . The additional low and high shelving filters allow for a broad-band correction of the frequenc curve,
while the parametric filters can be used to process narrow frequenc bands (mains hum, feedback, etc.).
Fig. 3.2: Typical roll-off function
With roll-off we usuall refer to a limitation of frequenc bands b means of high or low pass filters.
If ou set the LEVEL control at -15dB, the BANDWIDTH control full left and the FREQUENCY control
somewhere between 50 and 100Hz, ou have a ver steep low-cut filter. This will eliminate rumble and
breathing noises ver effectivel without affecting the sound.
At the high cut side ou can reduce tape hiss for example. Use this feature with caution however to prevent the
material from becoming muffled or sharp. It is advisable to use a dedicated denoiser like the BEHRINGER
MULTIBANDDENOISER SNR2000 to effectivel eliminate tape noise. The TUBE ULTRA-Q is well suited for
in-the-field problem solving when unexpected hiss arises.
3.3 Equalizers as creative audio tools
The TUBEULTRA-Q is an indispensable audio tool for application in recording studios, stage pla s or radio
dramas. You can use it to distort voices, create telephone sounds and filter instruments to make them fit into
the mixdown.
The charts printed below give ou some clues as to the acoustic significance of specific frequencies. Please
use them as suggestions for our own experiments with the TUBEULTRA-Q.
3. APPLICATIONS
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TUBE ULTRA-Q T1951
Center frequency (Hz)
1/3 octave Effects on music
31 to 63
Fundamentals of bass drum, tuba, double bass and organ.
These frequencies give music a sense of power. If over-
emphasized they make the music "muddy". The 50 or 60
Hz band is also used to reject AC mains hum.
80 to 125 Fundamentals of lower tympani. Too much boost produces excessive "boom". 100 or 125 Hz are also used for hum
rejection.
160 to 250 Drum and lower bass. Too much boost produces excessive "boom". Also useful for 3rd harmonic mains hum
rejection.
315 to 500 Fundamentals of strings and percussion.
630 to 1k Fundamentals and harmonics of strings, keyboards and percussion. Boosting the 600 to 1 kHz range can make
instruments sound horn-like.
1.25k to 4k
Drums, guitar, accentuation of vocals, strings and bass.
Too much boost in the 1 to 2 kHz range can make
instuments sound tinny. Too much boost anywhere
between 1 to 4 kHz can produce "listening fatigue".
5k to 8k
Accentuation of percussion, cymbals and snare drum.
Reduction at 5 kHz makes overall sound more distant and
transparent. Reduction of tape hiss and system noise. The
1.25 to 8 kHz governs clarity and definition.
10k to 16k Cymbals and overall brightness. Too much boost causes
sibilance. Reduction of tape hiss and system noise.
Tab. 3.1: Effects of equalization on music reproduction
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TUBE ULTRA-Q T1951
Center frequency (Hz)
1/3 octave Effects on voice
40 to 125 Sense of power in some outstanding bass singers.
160 to 250 Voice fundamentals.
315 to 500 Important for voice quality.
630 to 1k Important for voice naturalness. Too much boost in the 315 to 1 kHz
range produces a telephone-like quality.
1.25k to 4k
Voice fricatives-accentuation of vocals. Important to speech
intelligibility. Too much boost between 2 and 4 kHz can mask certain
speech sounds e.g. "m", "b", and "v" can become indistinguishable.
Too much boost anywhere between 1 and 4 kHz can produce
"listening fatigue". Vocals can be highlighted by slightly boosting the
vocal at 3 kHz and at the same time slightly dipping the instruments
at the same frequency.
5k to 8k Accentuation of voice. The range from 1.25 to 8 kHz governs the
clarity of voice.
10k to 16k Too much boost causes sibilance.
Tab. 3.2: Effects of equalization on voice reproduction
+Use the SHELF function to create a small lift in the upper frequencies, this is especially useful
hen using analog tape. Trying to recover lost brilliance is al ays tricky because you boost
hiss as ell. It is better to record bright, you can al ays mix back the brilliance.
3.4 The TUBEULT A-Q as tube interface
If ou want to use the TUBE ULTRA-Q purel as tube interface switch off all filters with their respective IN/OUT
switches but keep the master IN/OUT switch engaged.
Now ou can add upper harmonics b turning up the WARMTH control. Percussive instruments gain in punch
while instruments that are rich in harmonics like horns gain transparenc and brilliance.
Connect our TUBEULTRA-Q via the channel or subgroup inserts of our mixer. This wa ou can add tube
sound to selected instruments or groups of instruments. The TUBEULTRA-Q is also ver adapt to processing
the entire mix. You can of course combine the tube and parametric equalizer functions of the TUBEULTRA-Q.
3.5 EQ-ing a P.A. system
Parametric equalizers can also be combined with conventional graphic equalizers. The application of both is
conceivable in a P.A. s stem: the graphic equalizer can be used for broad-band corrections of the frequenc
response, for example, to simulate a tone control circuit, to adjust the sound of specific speaker s stems or to
enhance the low-range response and/or to make up for high-frequenc loss caused b room acoustics. The
TUBE ULTRA-Q can then be used for the detailed correction and the notching out of resonances.
Before ou insert an equalizer in our sound reinforcement s stem, ou should clearl define its tasks. If ou
fail to set up the EQ properl , it might deteriorate the sound image more than if ou used no sound-processing
device at all.
In a sound reinforcement s stem equalizers are used in three major areas of application:
1. Reducing the risk of feedback, while increasing the overall volume level.
2. Improving the natural sound of music.
3. Improving the intelligibilit of speech.
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TUBE ULTRA-Q T1951
It is quite obvious that compromises must be made to meet these requirements. In rooms with poor acoustics
or a high level of background noise, both natural sound and acoustic power can usuall not be realized
simultaneousl . Priorit must be given to one of these qualit -improving measures.
However, it should be noted that even a perfectl natural sound is useless if the audience has difficulties
understanding what a speaker sa s, for example at an election campaign rall !
Before ou start equalizing our s stem it will be useful to pla back some music or speech program without
equalization. If the sound is distorted ou should first tr to eliminate this problem. In order to get a feel for the
room acoustics it might be helpful to sweep a sine tone generator over the entire audio range (i.e. the
frequenc range from 20Hz to 20 kHz), which is better than pla ing back a signal consisting of pink noise, as
it will enable ou to identif weak points (room resonances, distortion, rattling noise) of both s stem and
location. In particular, the critical range between 2 and 4 kHz should be tested (if required, use the
TUBEULTRA-Q as a band-pass filter to limit the frequenc range). If ou detect an problems, these are
definitel caused b the s stem itself and should not be fixed with an equalizer!
Finall , use the TUBEULTRA-Q to fine-tune the s stem.
+If extreme equalizer settings are necessary to achieve a usable frequency response, the alarm
bell should start ringing!
This does not mean that such settings should generall not be used, often enough the cannot be avoided if
the room acoustics are poor. Nevertheless, ou should alwa s tr to change the room acoustics before ou
start tweaking the response curve drasticall .
Once the basic setting has been found, ou can fine-tune the s stem using music and speech signals. If ou
own a real-time anal zer (RTA) make sure that the measuring microphone is properl positioned. It should be
placed directl within the dispersion field of the sound s stem without being disturbed b acoustic character-
istics of the room. Avoid placing it behind curtains, less than 1 m awa from the walls, or on an open balcon ,
as this would impair our measurements.
We recommend that ou move the measuring mic on a circular line in front of the stage, so that ou can
compare the measured results. In this context it should be made sure that the frequenc response diagrams
do not differ excessivel from each other. If ou encounter an problems, change the position of the measuring
mic or check the s stem for proper phase.
Please verif that an background noise is at least 6dB (better 10dB) lower in level than our operating level;
otherwise ou cannot trust our measurements!
Once the s stem has been adjusted as accuratel as possible to ield the desired response curve, walk
around in the audience area and listen to the sound produced at various places. Remember to give our hearing
some pauses during the test and use different music or speech programs, so that ou get a feel for the
response characteristics of the sound s stem.
It takes a lot of time and patience to set up an equalizer properly!
Additionall , ou could experiment with a stage or house microphone directl connected to the anal zer, as
this will give ou some clues as to local reflections, acoustic resonances and the lateral dispersion character-
istics of the speakers. Once the overall adjustment of the sound s stem has been completed, an further
corrections should not be made on the s stem itself but in the respective channels of the mixing console, in
particular, when ou find that certain microphones are susceptible to feedback.
Inserting an equalizer in the signal path
The best point to insert the TUBEULTRA-Q in the signal path depends on the task on hand: basicall , it can
be inserted in the line insert points of the mixing console, subgroup inserts, subgroup outputs, effect paths or
between signal processor(s) and mixing console/power amp, etc.
If ou use a dela line unit (e.g. used in sound s stems with additional room speakers) to make up for run-time
differences, the TUBEULTRA-Q can be inserted either before or after the dela line unit.
If several similar speaker s stems are controlled simultaneousl (e.g. in a conference room), and if these
s stems are positioned at different distances to the stage, ou can use a dela line unit with multiple outputs
providing different dela times. In such a case the TUBEULTRA-Q should be inserted before the dela line
unit.
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TUBE ULTRA-Q T1951
In complex sound reinforcement s stems comprising different speakers located in var ing acoustic
environments (e.g. theaters with front speakers, various side-fill speakers and/or balcon speakers) each
single time-dela ed channel should be equipped with a separate TUBEULTRA-Q, as this is the onl wa to
make provision for var ing room acoustic and to adapt the speakers specificall .
What equalizers cant do
Equalizers are not a miracle cure for poor audio s stems, but can be highl useful and efficient audio tools to
musicall fine-tune such a s stem. Fine-tuning often delivers astounding results in terms of acoustic power
and overall sound qualit . Equalizers are definitel the most important accessories of our audio s stem. The
can work wonders when the are used properl , just as the old sa ing goes:
Its the tone that makes the music!
4. TECHNICAL BACKGROUND
4.1 Function
Parametric equalizers represent the most advanced form of equalization s stems. Basicall , the user has
control over the three parameters that define the so-called Gaussian equalization curve: bandwidth, frequenc
and amplitude boost/cut. Unlike graphic equalizers which provide a series of adjacent frequenc bands to
approach a specific frequenc , parametric equalizers allow for selecting a specific frequenc directl . The can
be used to realize complex frequenc curves with highest precision. Although the acoustic results of specific
equalizer settings cannot be predicted as easil as on graphic equalizers, parametric EQs are professional
audio tools of highest qualit . It will certainl pa to invest some time to stud their functioning principle and get
a feel for the wa in which the can be used to modif the program material.
The newl developed UTC circuit provides subtle sound enhancement rather than show effects processing. In
particular, digital workstations can be considerabl enhanced in their sound character. You are free to use the
TUBEULTRA-Q before the recording sessions or later when ou mix down the music ou recorded. You can
also use it to brighten up entire MIDI productions or even movie sound recordings and thus give them their
finishing touch.
Apart from the corrective function ou can also use the TUBEULTRA-Q as a creative tool. The TUBEULTRA-Q
is an indispensable audio tool for application in recording studios, stage pla s or radio dramas. You can use it
to distort voices, create telephone sounds and filter instruments to make them fit into the mixdown. All bands
are highl flexible with the possibilit to achieve ver narrow bands. In this respect the TUBEULTRA-Q is
superior to a graphic equalizer.
4.2 The Constant-Q principle
One of the most important features an graphic or parametric equalizer has to offer is the independent control
of its various parameters. The special state-variable filters of the TUBEULTRA-Q use the so-called
Constant-Q principle which prevents the parameters frequenc , bandwidth and amplitude from
influencing each other. In the same wa , the mutual influence of the individual frequenc bands is avoided,
which is a fundamental requirement as it allows for clearl defined and repeatable filter settings. When several
filters are used simultaneousl , the resulting overall filter curve can be calculated b adding/subtracting the
single band-specific filter curves.
4.3 The concept of parallel filters
Unlike conventional parametric equalizers the TUBEULTRA-Q features a parallel filter configuration, which
offers a decisive advantage over series-t pe configurations: with parallel filters it is possible to reduce to a
minimum the phase shifts and dela s usuall associated with filters, which is the reason wh the TUBEULTRA-Q
is such a musical device.
Naturall , this concept, too, is subject to a few limitations: unlike series-t pe filter configurations the concept
of parallel filters allows onl to a limited extent for an extreme boost/cut of frequencies. However, as extreme
settings are usuall the result of an improperl adjusted sound image, it is imperative that deficiencies of this
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TUBE ULTRA-Q T1951
kind be identified and eliminated, before the actual musical fine-tuning of the sound image takes place. Still,
extreme settings can be realized b overlapping the frequencies of the individual bands.
4.4 On phase shift and time delay
An analog filter, be it graphic or parametric, produces a certain amount of phase shift.
Particularl in narrow-band filters this phase shift leads to specific dela of the audio signal: the narrower the
filter and the higher the gain, the greater the time dela . In certain applications, the effect on the sound image
can be anno ing.
Although the TUBEULTRA-Q, owing to its unique concept, produces considerabl less phase shift and hence
time dela than conventional parametric equalizers, this effect should nevertheless be taken into account.
+Please also note that filters sho a natural tendency to produce a ringing sound as their
band idth is narro ed, an effect that is caused by system-intrinsic noise modulation that
occurs ith any kind of filter. It is therefore recommended that you set all filters not in use to a
mid-travel position or simply s itch them off to minimize these side effects as effectively as
possible.
4.5 Tubes used in the TUBEULT A-Q
A closer look at developments and trends in audio technolog shows that tubes are currentl enjo ing a
renaissance, in a time when even amateur musicians are free to use digital effects processors and recording
media, and ever more affordable digital mixing consoles are becoming a natural part of the equipment of man
semiprofessional studios. The manufacturers tr with ever new algorithms to get the most out of DSPs (Digital
Signal Processors), the heart of an digital s stem.
Still, man audio engineers, particularl old hands often prefer using both old and new tube-equipped devices.
As the want to use their warm sound character for their productions, the are read to accept that these
goodies produce a higher noise floor than modern, transistor-based devices. As a consequence, ou can find
a variet of tube-based microphones, equalizers, pre-amps and compressors in toda s recording and
mastering environments. The combination of semiconductor and tube technologies gives ou the additional
possibilit of using the best of both worlds, while being able to make up for their specific drawbacks.
4.5.1 Tube history
Due to man patent litigations, it is difficult to determine exactl when the tube was born. First developments
in tube technolog were reported between 1904 and 1906. It was a research task of that time to find a suitable
method for receiving and rectif ing high frequencies. On April 12, 1905, a certain Mr. Fleming was granted a
patent for his hot-cathode valve which was based on Edisons incandescent lamp. This valve was used as a
rectifier for high-frequenc signals. Robert van Lieben was the first to discover (probabl b chance) that the
anode current can be controlled b means of a perforated metal plate (grid), one of the milestones in the
development of amplification tubes. In 1912, Robert van Lieben finall developed the first tube for the amplifica-
tion of low-frequenc signals. Initiall , the biggest problem was to produce sufficient volume levels, which is
wh resonance step-ups (though impairing the frequenc response) were used to maximize the attainable
volume. Later, the objective was to optimize the electroacoustic transducers of amplifiers in such a wa that a
broad frequenc band could be transmitted with the least distortion possible. However, a tube-specific problem
is its non-linear amplification curve, i.e. it modifies the sound character of the source material. Despite all
efforts to ensure a largel linear frequenc response, it had to be accepted that tube devices produce a bad
sound. Additionall , the noise floor generated b the tubes limited the usable d namics of connected storage
media (magnetic tape machines). Thus, a one-to-one reproduction of the audio signals d namics (expressed
as the difference between the highest and lowest loudness levels of the program material) proved impossible.
To top it all, tube devices required the use of high-qualit and often costl transducers and sophisticated
voltage supplies.
With the introduction of semiconductor technologies in the field of audio amplification it soon became clear that
the tube would have to give wa to the transistor, as this device featured an enormousl enhanced signal-to-
noise ratio, less complex power suppl and improved frequenc response. Plus, semiconductor-based circuits
can be realized much more easil for less mone . Two decades later, the introduction of binar signal
processing meant the beginning of a new era of recording media that provided plent of d namic response and
4. TECHNICAL BACKGROUND
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TUBE ULTRA-Q T1951
allowed for loss-free cop ing of audio signals. As digital media were enhanced, however, man people began
to miss the warmth, power and liveliness the knew from analog recordings. This is wh purists still toda
consider digital recordings as sterile in sound.
4.5.2 Design and functional principle of tubes
Tubes can be roughl classified according to the number of electrodes the use. There are tubes with two,
three or five electrodes usuall referred to as diodes, triodes or pentodes.
Fig. 4.1: Diode
The diode contains two electrodes in a vacuum glass bulb that have electrical connection to the outside. The
vacuum allows for a free movement of electrons. When one of the electrodes is heated up (= thus becoming a
cathode), it begins to emit electrons. When a positive dc voltage is applied to the other electrode (= anode), the
negative electrons start to wander from the cathode to the anode. With reverse polarit between cathode and
anode, a current flow is not possible because the unheated anode emits more or less no electrons. This design
was used, for example, as a rectifier in the power supplies of amplifiers. The magnitude and velocit of the flow
of electrons depend on the cathodes temperature, the material it consists of, and the magnitude of the anode
voltage. When the electrons hit the anode the produce heat that is dissipated b using large anode plates.
Fig. 4.2: Triode
The triode has an additional metal grid between anode and cathode. B appl ing a negative voltage, this grid
can be used to control the internal resistance of the tube, and hence the anode current. When the grid bias
voltage (voltage between cathode and grid) becomes negative, the current flowing to the anode is reduced
because the negativel charged grid repels the arriving electrons. As a consequence, there are less electrons
to reach the anode. When the bias voltage is raised towards zero, the flow of electrons accelerates. When it
finall becomes zero or even positive, the grid current begins to flow which considerabl reduces the current
flowing to the anode and can possibl destro the tube. Triodes are most commonl used in pre-amps, often
in pairs arranged in one tube (twin triode).
Fig. 4.3: Pentode
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TUBE ULTRA-Q T1951
In a triode the capacitance between grid and anode is a problem with regard to high frequencies and large
amplification factors. For this reason, the pentode has a positivel charged screen grid between the control grid
and the anode. However, the positive charge of the screen grid attracts electrons emitted from the anode plate
when it is hit b arriving electrons. To prevent this electron emission, a decelerating or suppressor grid is
placed between anode and screen grid. As it is negativel charged it blocks the electrons, so that the cannot
reach the screen grid. Pentodes are most commonl used in power stages.
4.5.3 Properties of tubes
In general, the saturation (overdriving) of both transistor and tube-based circuits results in various t pes of
distortion. These phenomena are quite complex in the real world, but for the sake of a straightforward
mathematical description we are going to classif them as linear and non-linear distortion. Linear distortion is
produced b frequenc -dependent amplification or attenuation processes such as occurs in all kinds of filters
and equalizers. Linear-distortion signals have the same frequenc portions both on the input and output sides,
but with different phase positions and amplitudes. Non-linear distortions have additional harmonics and
distortion components that were not contained in the original input signal.
For example, when the plainest of all oscillations, a sine wave with a fixed frequenc f, is overdriven, new
oscillations with frequencies of 2*f, 3*f, etc. (integral multiples of the original frequenc ) are produced. These
new frequencies are referred to as upper harmonics grouped as odd and even harmonics. Unlike the transistor,
saturated tubes mostl produce even harmonics which are perceived b the human ear as more pleasant in
sound than odd harmonics. Another important aspect lies in the fact that tubes produce distortion more
graduall than transistors, which is wh we speak of the saturation of a tube stage. When ou overdrive a
transistor ou get a sudden square deformation of the sine signal applied at the input, which produces an
extreme harmonic spectrum at the output.
Non-linear distortions are measured with a distortion factor that consists of the total harmonic distortion [k] and
partial harmonic distortions [kn]. The latter are defined as the ratio between the voltage of a single harmonic
and the voltage of the distorted overall signal. Thus, the content of even harmonics is expressed as k2, k4, ...
and that of odd harmonics as k1, k3, ...
kU
U
nn
ges
=
Formula for calculating partial harmonic distortion
The total harmonic distortion is the root of all squared distortion factors of the second and third degrees. Since
the higher harmonics have onl little impact on the measured results, the can be neglected.
kkk=+
2
23 2
Formula for calculating total harmonic distortion
In tube circuits the distortion factor k2 is used to describe an effect which the human ear classifies as
pleasant. Also the frequenc bands in which distortion occurs pla an important role because the human ear
differentiates ver clearl in the frequenc range of human speech.
4.5.4 The best of both orlds
Despite man efforts neither manufacturers nor developers have succeeded so far in simulating these positive
properties of the tube b means of other devices. Additionall , the natural capabilities of the tube to act as a
soft limiter can onl be mimicked with highl sophisticated circuitr . Toda s studio technolog requirements
are therefore met b a combination of both high-grade semiconductor and tube technologies. In this context,
tubes no longer serve their original purpose as amplifiers, but are used for the detailed shaping of sound.
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TUBE ULTRA-Q T1951
4.5.5 UTC circuit
In
Out
WARMTH
Fig. 4.4: UTC circuit
The TUBEULTRA-Q splits up the audio signal applied at the input, and processes it differentl for both signal
paths. Each of the two tube halves amplifies the original signal and the signal modified in its phase spectrum
(twin triode). Additional harmonics are produced b slightl overdriving the tube stage. When the two signals
are processed b the UTC circuit, the interference noise found in conventional tube circuits can be largel
eliminated, and the actual tube effect be added graduall . The more ou turn the Warmth control to the right,
the more tube sound will be added to the original signal.
4.5.6 Studio applications
In a recording studio tubes do not perform the same task as the do in an overdriven guitar amp, where the
considerabl higher saturation of the tube(s) leads to a full and often deliberate modification of the input signal
(in man cases combined with a heav increase in noise floor levels). In the studio more subtle effects are
needed. Here, tube circuits add life to the signals tonal character and increase its power to make itself heard.
Often, tubes also increase the signals perceived loudness (in relation to the unprocessed signal), i.e. the
perceived loudness goes up although the volume level remains the same. This is because the d namic range
of the applied audio signal is limited b the tube circuit, while the amplitude of the signal with the lowest
loudness is raised. Thus, increasing tube saturation produces a slight compression effect over the entire
d namic range.
A similar effect can be perceived when analog tape is saturated. This saturation effect also compresses the
recorded audio material and produces additional harmonics.
4. TECHNICAL BACKGROUND
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