Alto BK 2.0 User manual

BK 2.0
User's Manual
LTO
RR
www.altoproaudio.com
Version 2.0 Dec. 2002
EnglishEnglish
COMPRESSOR /LIMITER /GATE

1
SAFETY RELATED SYMBOLS
CAUTION
RISK OF ELECTRIC SHOCK
DO NOT OPEN
Protective Grounding
Make sure to connect the protective grounding to prevent any
electric shock before turning ON the apparatus.
Never cut off the internal or external protective grounding wire
or disconnect the wiring of protective grounding terminal.
The symbol is used to indicate that some hazard-
ous live terminals are involved within this apparatus,
even under the normal operating conditions.
The symbol is used in the service documentation
to indicate that a specific component shall be only
replaced by the component specified in that docu-
mentation for safety reasons.
Protective grounding terminal.
Alternating current /voltage.
Hazardous live terminal.
ON: Denotes the apparatus is turned on.
OFF: Denotes the apparatus is turned off, because it uses
the single pole switch, be sure to unplug the AC power to
prevent any electric shock before you proceed with your
service.
WARNING: Describes precautions that should be
observed to prevent the danger of injury or death to
the user.
CAUTION: Describes precautions that should be
observed to prevent danger of the apparatus.
WARNING
Power Supply
Ensures the source voltage matches the voltage of the
power supply before turning ON the apparatus.
Unplug this apparatus during lightning storms or when
unused for long periods of time.
External Connection
The external wiring connected to the output hazardous live
terminals requires installation by an instructed person, or the
use of ready-made leads or cords.
Do not Remove any Cover
There are maybe some areas with high voltages inside,
to reduce the risk of electric shock, do not remove any
cover if the power supply is connected.
The cover should be removed by qualified personnel
only.
No user serviceable parts inside.
Fuse
To prevent a fire, make sure to use fuses with specified stan-
dard (current, voltage, type). Do not use a different fuse or
short circuit the fuse holder.
Before replacing the fuse, turn OFF the apparatus and dis-
connect the power source.
Operating Conditions
This apparatus shall not be exposed to dripping or spl-
ashing and that no objects filled with liquids, such as
vases, shall be placed on this apparatus.
To reduce the risk of fire or electric shock, do not expose
this apparatus to rain or moisture.
Do not use this apparatus near water.
Install in accordance with the manufacturer's instructions.
Do not install near any heat sources such as radiators,
heat registers, stoves, or other apparatus (including amp-
lifiers) that produce heat.
Do not block any ventilation openings.
No naked flame sources, such as lighted candles, should
be placed on the apparatus.
IMPORTANT SAFETY INSTRUCTIONS
Read these instructions.
Heed all warnings.
Follow all instructions.
Keep these instructions.
Only use attachments/accessories specified by the manu-
facturer.
Power Cord and Plug
Do not defeat the safety purpose of the polarized or
grounding type plug. A polarized plug has two blades
with one wider than the other. A grounding type plug
has two blades and a third grounding prong. The wide
blade or the third prong are provided for your safety.
If the provided plug does not fit into your outlet, consult
an electrician for replacement of the obsolete outlet.
Protect the power cord from being walked on or pinched
particularly at the plug, convenience receptacles, and
the point where they exit from the apparatus.
Cleaning
When the apparatus needs a cleaning, you can blow off
dust from the apparatus with a blower or clean with a rag
etc. Don't use solvents such as benzol, alcohol, or other
fluids with very strong volatility and flammability for cleaning
the apparatus body.
Clean only with a dry cloth.
Servicing
Refer all servicing to qualified personnel. To reduce the
risk of electric shock, do not perform any servicing other
than that contained in the operating instructions unless
you are qualified to do so.
Servicing is required when the apparatus has been dam-
aged in any way, such as the power supply cord or plug
is damaged, liquid has been spilled or objects have fallen
into the apparatus, the apparatus has been exposed to
rain or moisture, does not operate normally, or has been
dropped.

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PREFACE
Dear Customer:
For our LTO AUDIO TEAM, music and sound are more then a job...are first of all passion and let us say...our obsession!
We have been designing professional audio products for a long time in cooperation with some of the major brands in
the world in the audio field.
The LTO line presents unparalleled analogue and digital products made by Musicians for Musicians in our R&D Centers
in Italy, Netherlands, United Kingdom and Taiwan. The core of our digital audio products is a sophisticated DSP (Digital
Sound Processor) and a large range of state of the art algorithms which have been developed by our Software Team
for the last 7 years.
Because we are convinced you are the most important member of LTO AUDIO TEAM and the one confirming the quality
of our job, we like to share with you our work and our dreams, paying attention to your suggestions and your comments.
Following this idea we create our products and we will create the new ones! From our side, we guarantee you and we will
guarantee you also in future the best quality, the best fruits of our continuous researches and the best prices.
Thank you very much.
LTO AUDIO TEAM
Thanks for choosing LTO BK 2.0 Compressor/Limter/Gate and thanks for choosing one of the results of LTOAUDIO
TEAM job and researches.
Our LTO BK 2.0 is the result of many hours of listening and tests involving common people, area experts, musicians
and technicians.
The results of this effort is that you can acquired an extremely efficient and universal dynamics processor. It Contains
several new circuit design which make the unit an ultimate dyna mic processor: intelligent program recognition, interactive
Expander/Gate and a new Dynamic Enhancer.
Nothing else to add, but that we would like to thank all the people that made the LTO BK 2.0 a reality available to our
customers, and thank our designers and all the LTO staff, people who make possible the realization of products containing
our idea of music and sound and are ready to support you, our customers, in the best way, conscious that you are our best
richness.

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TABLE OF CONTENTS
1. INTRODUCTION........................................................................................................................................4
2.1 Some technical stuff
2. THE CONCEPT BEHIND..........................................................................................................................4
2.2 Voltage Controlled Amplifier (VCA)
2.3 Inputs
3. CONTROLS................................................................................................................................................6
3.1 Expander/Gate Section
3.2 Compressor Section
3.3 Dynamic Enhancer Section
3.4 The Rear Panel
4. READY TO ROLL?....................................................................................................................................9
4.1 Expander/Gate Section
4.2 Compressor Section
4.3 Limiter Section
6. TECHNICAL SPECIFICATIONS .................................................................................................................................13
7. BLOCK DIAGRAM......................................................................................................................................................14
5. INSTALLATION AND CONNECTION.....................................................................................................11
5.1 Mains Connection
5.2 Audio Connection
5.3 Rack Mounting
8. WARRANTY ...............................................................................................................................................................15

1. INTRODUCTION
You are now the owner of an LTO BK 2.0 Compressor/Limiter/Gate. The BK 2.0 is a very powerful dynamic processor. We
have included in it several innovative circuit designs that make the BK 2.0 a very versatile processor: smart and fast recognition
of the program, adjustable Expander/Gate and very low distortion Voltage Control Amplifier (VCA).
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Feature List:
Smart Knee Control Compressor (SKC)
Soft knee or hard knee? This is the question! SKC combines both: In the "soft knee" mode you control the program
material so that the compression will be the most musical and inaudible. ON the other end, the hard knee function is
used for better precision, limiting signal peaks with precision and will allow you to add creativity to the dynamic processing.
This function also allows you to protect other equipment in the signal loop against distortion.
The AUTO Function
Your BK 2.0 includes and AUTO function switch on the front panel. Thanks to the AUTO function attack and release times of
the program materials are automatically analysed. Then the dynamic range of the program is heavily compressed in a very
musical way so that there will not be any audible breathing or pumping effect.
Smart Ratio Control expander (SRC)
Durinmusic pauses or when a quiet session occurs, the noise floor maybe highly amplified and this effect
may be exaggerated because of inappropriate use of the compression ratio. The SRC control will adjust the
expansion depending on the input signal so that those signals, which are slightly above the noise floor level,
will get the major benefits.
Smart Gate Control peak limiter (SGC)
This function includes two important functions: Clipper and program limiter. The peak limiter will be activated
above a certain threshold that is adjusted by the User and will radically restrict signal peaks. But what about if
the threshold of the Limiter is surpassed only for a few milliseconds? SGC will turn on automatically and reduce
the output signal so that you will not hear any distortion. Smart, isn't it? The SGC proves to be very efficient in
loudspeaker protection and to reduce undesired peaks in digital situations.
Ok,Ok, you do not want to get advantage of our AUTO function and be the Master of your own mix.
We have provided your BK2.0 with User Adjustable attack and release time for the best total manual control.
Attack and Release Controls:
2.1 Some technical stuff
Good old analog technology: It will allow us to manufacture audio equipment with a very high dynamic range: up
to 125 dB. But the dynamic range of digital equipment is more or less 25 dB less. A further reduction in dynamic
range occurs with the use of tape recorders and/or vinyl records.
2. THE CONCEPT BEHIND
2.1.1 It is not just Music
Yes, a piece of electronic will produce some noise. When the current flows through a conductor this will generate
a certain movement of the electrons and therefore: noise. And throughout the whole spectrum of audio. Imagine
what happens when this inherent noise will be amplified. Yes, today one can use "low-noise" components but still
such components will present a certain level of residual noise.
For example with tape recorders it will not be possible to get an S/N (signal to noise) ratio better than 70dB.
This level would not be accepted today by the increased sensitivity of the Listeners. It is possible to improve the
performance of a tape recorder: Absolutely no!

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2.1.2 Introducing Audio Dynamics
The human ear can detect the noise generating by falling leaves as well as the roar generated by the taking off space
shuttle. Unfortunately no analog, nor digital device can reproduce such wide spectrum. Please look at Chart. 1 and you
will see the difference if dynamic capacity of various devices when compare to the human ear. More problems occur
when handling high level signals and low level signals. When you reach the high level limit you may incur in distortion
because of the dynamic range of the instrument therefore a certain "reserve" must be maintained to avoid distortion.
This reserve is known as "headroom" and it is usually set at 10-20 dB. Would not be easier just to reduce the operating
level? Yes it would but you would put low level music signals at the same level of the basic noise floor so the overall
quality of the signal would be highly deteriorated. Please look at Chart. 2 and note the Usable dynamic range (including
headroom) versus high level distortion generated by peaks, and Noise floor level.
Chart.1: The dynamic range capabilities of various devices
Chart.2: The interactive relationship between the operating level and the headroom
So the operating level must be as high as possible but not high enough to generate distortion.
Thriky uh?
There is a very easy way to obtain this. With the volume knob in hand you increase the volume during
low passages and decrease the volume during loud passages. Unfortunately even the Great Houdini
would not be fast enough to monitor carefully the speed of the musical signal and it would be impossible
to detect signal peaks and consequently levelling them out. Manual control is therefore out of question.
The answer is AGC (automatic gain control); a device that will monitor the signal in real time and that
will adjust the gain for the best S/N ratio without producing distortion. So, the name of this device is
"Compressor/limiter".
Try to measure the dynamic range of musical instruments. You will find out that your ear will handle such
range. Your audio equipment will not and distortion and overloading will be generated.
To avoid these, compressor/Limiters will be used. Both Compressors and Limiters more or less do the same
job but Limiters brutally limit the audio signal above a set threshold, while Compressors handle signal in a
much more civilised way and over a wide range of levels. If an audio signal exceed the threshold set by the
User the limiter will kill any audio signal above that threshold. Period! Also Compressors perform their function
when the audio signal exceed a certain threshold but the signal is not killed brutally. The audio signal will be
reduced in gain in proportion with the amount above the set threshold.
2.1.3 More technical stuff about Compressor/Limiters
Clipping Signal heavily distrortedClipping Signal heavily distrorted
Low level signal drowned out by noiseLow level signal drowned out by noise
Clipping Aera
Noise Aera

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2.1.4 More about noise: Expanders and Noise-Gates
A lot of instruments such as microphones, amplifiers, guitar pickups, etc generate some noise, either at low frequ-
encies (hum) or at high frequencies (hiss) Such noise will inevitably interfere with the quality of your audio signal.
Now, if you scream into a microphone you will not hear the noise generated by such microphone because such
noise will be "masked" by the higher level of the signal, your voice in this case.
But if you sing into your microphone more gently in a soft passage, the level of the signal generated by your voice
will get much closer to the floor noise level and such floor noise will become disturbing. In order to kill this problem
Expanders and noise-gates are used. An expander is the opposite of a compressor: attenuating the signal when the
amplitude drops they can limit the floor noise.
Now, we do not need dramatic expansion of a signal across the range, This would generate a resulting dynamic
range of over 150dB. For this reason the amplitude control will be applied only to those audio signals which are
below a set threshold. Those audio signals above the set threshold will not be affected. Noise-gate can be regarded
as a simple Expander. But the Expander will attenuate the audio signal continuously below the set threshold while
the noise-gate will simply dramatically cut-off the audio signal completely.
2.2 Voltage Controlled Amplifier (VCA)
The VCA is the soul of the BK 2.0 and it is one of the best components available today in his category thanks to its excellent
performances in terms of distortion, linearity, noise and temperature stability.
2.3 Inputs
2.3.1 Take it easy: Balanced Inputs
To make your life easy and clean we have provided BK 2.0 with electronically balanced inputs. Even if you
operate at high signal levels, hum and noise will be reduce automatically. There is also a servo-function that will
automatically adjust the internal level when unbalanced connectors are detected. The correction if of 6dB and
it will avoid differences in level in between input and output signal.
3. CONTROLS
Pic.1: Front panel layout of the BK 2.0
EXP / GATE COMPRESSOR / LIMITER ENHANCER
THRESHOLD THRESHOLD RATIO ATTACK AUTO RELEASE OUTPUT IN/OUT PROCESS
dBu dBu n:1 ms dB EFFECTIN
CLOSE
OFF +10
-70 0
-50 -15
-30
-40 +20
-30 +10
-20 0
-10
1LIM
1.5 8
25
2.5
0.1 200
1150
10 100
50
50m 4
0.1 2
0.3 1
0.5
OFF 6
15
2 4
3
-20 +20
-14 +14
-6 +6
0
EXP / GATE
THRESHOLD
dBu
CLOSE
OFF +10
-70 0
-50 -15
-30
-30
ON
OFF
POWER
CH1
CH2
AUTO CH1 IN AUTO CH2 IN
30 20 15 10 6 4 2 1
GAIN REDUCTION (dB)
R
LTO
COMPRESSOR
/LIMITER/GATE
BK2.0
COMPRESSOR / LIMITER ENHANCER
THRESHOLD RATIO ATTACK AUTO RELEASE OUTPUT IN/OUT PROCESS
dBu n:1 ms dB EFFECTIN
-40 +20
+10
-20 0
-10
1LIM
1.5 8
25
2.5
0.1 200
1150
10 100
50
50m 4
0.1 2
0.3 1
0.5
OFF 6
15
2 4
3
-20 +20
-14 +14
-6 +6
0
The BK 2.0 presents with right and left channels. Each channel is equipped with the same control elements: 2 push-button
switches, 7 rotary controls and 11 LED's.
3.1 Expander/Gate Section
Pic.2: Controls of Expander/Gate section
12
EXP / GATE
THRESHOLD
dBu
CLOSE
OFF +10
-70 0
-50 -15
-30
-30
1.Threshold Control
This control adjust the threshold level for the Expander / Gate Section in the range of Off to +10dBu. Signals
below this level cause attenuation.

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2.Close LED
This LED illuminates when expansion occurs.
456 8 7 9 3
10
Pic.3: Controls of the Compressor/Limiter section
COMPRESSOR / LIMITER
THRESHOLD RATIO ATTACK AUTO RELEASE OUTPUT IN/OUT
dBu n:1 ms dB EFFECT
IN
-40 +20
+10
-20 0
-10
1LIM
1.5 8
25
2.5
0.1 200
1150
10 100
50
50m 4
0.1 2
0.3 1
0.5
-20 +20
-14 +14
-6 +6
0
ENHANCER
PROCESS
OFF 6
15
2 4
3
30 20 15 10 6 421
CH1
CH2
AUTO CH1 IN AUTO CH2 IN
GAIN REDUCTION (dB)
sec
3.2 Compressor Section
Engage this switch to activate the corresponding channel. It can be used to make an A/B comparison in be-
tween processed and unprocessed signal.
3. EFFECT Switch
4. THRESHOLD Control
This control adjusts the threshold level for the Compressor section in the range of -40dBu to +20dBu. The SKC
(Smart Knee Control) is applied to the audio signal, which is a maximum of 10dB above the set threshold.
Above such level (10dB) a hard knee compression will be applied.
5. Ratio Control
The ratio between the input and output level of audio signals exceeding the set threshold level is determined by this
control. This control is manually adjustable from 1:1 to LIM:1.
6.Attack Control
This control determines how fast the compressor is to respond to audio signals that will exceed the set threshold. It can be
manually adjusted from 0.1 to 200 milliseconds.
7. Release Control
This control determines how fast is the compressor to return to unity gain when the audio signal falls below the set
threshold level. It can be manually adjusted from 0.05 to 4 seconds.
8. Auto Switch
Who needs Attack and release control? Activate this switch and these controls will be deactivated. Attack and release
controls will be automatically set by the unit depending on the program material.
9.Output Gain Control
Through this control you can vary the output signal by a maximum of 20 dB. In this way you can recover a level
that had been lost because of the compression process.
10. Gain Reduction Meter
It indicated the gain reduction. The range displayed is 1 to 30 dB.
3.3 Dynamic Enhancer Section
11
Pic.4: Controls of the Dynamic Enhancer section
ENHANCER
PROCESS
OFF 6
15
2 4
3

8
11. PROCESS control
This control renews any high frequencies lost through the compression process for natural sounding dynamics control, which
can be varied from off to 6. Please note that the enhancer control is only used when compression is taking place.
3.4 The Back Panel
Pic.5: The Back Panel Layout Of The BK 2.0
13
12
15 14 16
OUTPUT INPUT
TIP = INPUT
RING = OUTPUT
SLEEVE=GROUND
OUTPUT INPUT
TIP = INPUT
RING = OUTPUT
SLEEVE=GROUND
CHANNEL 1 SIDECHAIN CHANNEL 2 SIDECHAIN
AC INPUT
95-120V/ 210-240V6 0-50Hz
Rated Power Consumption 8W
FUSE:
210-240V: T100mAL 250VAC
95-120V: 200mA 250VAC
REPLACE FUSE WITH
CORRECT TYPE ONLY
SERIAL
MODEL
21
3
21
3
The fuse-holder above the AC connector on the rear of the chassis has 3 triangular markers(please refer to the above
pictures), with two of these triangles opposing each other, your unit is set to the operating voltage printed next to these
markers.
To change, pull fuse-holder out and rotate 180 , then push in again.
THIS IS SET FOR
110V AC TO 120V
AC OPERATION
THIS IS SET FOR
220V AC TO 240V
AC OPERATION
12. Fuse holder / Voltage Selector
This is a dual voltage unit. Before you attempt to connect and operate the unit, please make sure that your local
voltage matches the voltage on the fuse-holder cover.
Caution: The fuse protecting the AC supplies circuits of this unit. The fuse can only be changed by a qualified
technician, in the event of a fault or changing the supply voltage. If the fuse continues to blow after replacing,
discontinue use of this unit before repaired.
220-240V
110-120V
110-120V
220-240V
13. AC Inlet
This connector is meant for the connection of the supplied main cord. Do not insert power cable into unit until voltage
has been correctly set. Do not plug power cable into AC power until voltage has been correctly set.
These connectors are used to input the signal source. You can input the signal via the balanced 1/4" TRS phone jack
or XLR connector.
14. Audio In
15. Audio Out
These connectors are used to output the signal. You can output the signal via the balanced 1/4" TRS phone jack or
XLR connector.
16. Sidechain Insert
The connector can be regarded as insert point, which allows the unit to be controlled externally, of course the con-
nector must be stereo (Ring output/Tip input). You can also use the connector as a control input (mono connector).

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4. READY TO ROLL?
4.1 Expander/Gate Section
Chart.3: Function of an expander
As we told you previously in this Manual the downward expander will reduce automatically the level of the audio signal when
such signal is below a set threshold. So the expander is the opposite of the compressor/limiter. We also explained to you how
the ratio curve of the expander is flat while a noise gate it is more brutal processor: It simply cut-off the entire signal below a
certain set threshold. The BK 2.0 is equipped with a new kind of expander, the SRC (Smart Ratio Control). The ratio of the
SRC is automatically adjusted according to the audio signal level. In fact, conventional expanders could easily cut part of the
musical program with unacceptable result:The gain changes become audible.
We have equipped the SRC with a non-linear ratio curve, which is soft and adjustable by the User. Thanks to the SRC low
passages close to noise floor level will be processed with a minute ratio of expansion while for signals of reduced level a higher
ratio will be used with resultant greater attenuation.
Chart.4: SRC Curve characteristics of the Adaptive Expander
4.1.1 Threshold Adjustment
The threshold control covers a very wide range and it is efficient with any working level. Turn the threshold control
fully counterclockwise and the Expander/Gate section will be completely off.
4.2 Compressor Section
4.2.1 Another Threshold Control?
The compressor threshold control sets the point where the input level starts to be reduced. Let's say the level is
+12dBu and the threshold control is set at +2dBu: In this case up to 10 dB can be compressed. If the input level
is the same and the control is set at 10dBu the maximum compression will be 22 dB, The operating range of the
threshold control is -40 to +20dBu. Turn the threshold control fully clockwise and you will get a threshold level of
+20dBu.
You must remember that the degree and the type of compression not only depend by the threshold control but
also by other controls such as Ratio, Attack and Release.
SRC CURVE