Nilfisk BK 2.0 User Manual

User's Manual

BK 2.0

COMPRESSOR /LIMITER /GATE

RR

LTO

www.altoproaudio.com

Version 2.0 Dec. 2002

English English

SAFETY RELATED SYMBOLS

CAUTION

RISK OF ELECTRIC SHOCK

DO NOT OPEN

The symbol is used to indicate that some hazard­ous live terminals are involved wit hin 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 docu­mentation 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 stan­dard (current, voltage, type). Do not use a different fuse or
short circuit the fuse holder.
Before replacing the fuse, turn OFF the apparatus and dis­connect the power source.

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.

Operating Conditions

This apparatus shall not be exposed to dripping or spl­ashing 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.

Follow all instructions.
Keep these instructions.
Heed all warnings.
Only use attachments/accessories specified by the manu­facturer.

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 dam­aged 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.

1

PREFACE

Dear Customer:

Thanks for choosing LTO BK 2.0 Compressor/Limter/Gate and thanks for choosing one of the results of LTO AUDIO
TEAM job and researches.

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 C enters
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.

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.

Thank you very much.

LTO AUDIO TEAM

2

TABLE OF CONTENTS

1. INTRODUCTION........................................................................................................................................4

2. THE CONCEPT BEHIND..........................................................................................................................4

2.1 Some technical stuff

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

5. INSTALLATION AND CONNECTION.....................................................................................................11

5.1 Mains Connection

5.2 Audio Connection

5.3 Rack Mounting

6. TECHNICAL SPECIFICATIONS .................................................................................................................................13

7. BLOCK DIAGRAM......................................................................................................................................................14

8. WARRANTY ...............................................................................................................................................................15

3

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).

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.

Attack and Release Controls:

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.

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.

2. THE CONCEPT BEHIND

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.

2.1.1 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!

4

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

Clipping Aera

Noise Aera

Chart.2: The interactive relationship between the operating level and the headroom

Clipping Signal heavily distrortedClipping Signal heavily distrorted

Low level signal drowned out by noiseLow level signal drowned out by noise

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".

2.1.3 More technical stuff about Compressor/Limiters

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.

5