Nilfisk ACL2 Pro User Manual
User's Manual
ACL2 PRO
COMPRESSOR /LIMITER /GATE
SAFETY RELATED SYMBOLS
CAUTION
RISK OF ELECTRIC SHOCK
DO NOT OPEN
This symbol, wherever used, alerts you to the presence of un-insulated and dangerous voltages within the product enclosure. These are voltages that
may be sufficient to constitute the risk of electric
shock or death.
This symbol, wherever used, alerts you to important operating and maintenance instructions.
Please read.
Protective Ground Terminal
AC mains (Alternating Current)
Hazardous Live Terminal
ON: Denotes the product is turned on.
OFF: Denotes the product is turned off.
WARNING
Describes precautions that should be observed to
prevent the possibility of death or injury to the user.
the recommended fuse type as indicated in this
manual. Do not short-circuit the fuse holder. Before
replacing the fuse, make sure that the product is
OFF and disconnected from the AC outlet.
Protective Ground
Before turning the product ON, make sure that it is
connected to Ground. This is to prevent the risk of
electric shock.
Never cut internal or external Ground wires. Likewise,
never remove Ground wiring from the Protective
Ground Terminal.
Operating Conditions
Always install in accordance with the manufacturer's
instructions.
To avoid the risk of electric shock and damage, do
not subject this product to any liquid/rain or moisture.
Do not use this product when in close proximity to
water.
Do not install this product near any direct heat source.
Do not block areas of ventilation. Failure to do so
could result in fire.
Keep product away from naked flames.
CAUTION
Describes precautions that should be observed to
prevent damage to the product.
WARNING
Power Supply
Ensure that the mains source voltage (AC outlet)
matches the voltage rating of the product. Failure
to do so could result in damage to the product and
possibly the user.
Unplug the product before electrical storms occur
and when unused for long periods of time to reduce
the risk of electric shock or fire.
External Connection
Always use proper ready-made insulated mains
cabling (power cord). Failure to do so could result
in shock/death or fire. If in doubt, seek advice from
a registered electrician.
Do Not Remove Any Covers
Within the product are areas where high voltages
may present. To reduce the risk of electric shock do
not remove any covers unless the AC mains power
cord is removed.
Covers should be removed by qualified service
personnel only.
No user serviceable parts inside.
Fuse
To prevent fire and damage to the product, use only
IMPORTANT SAFETY INSTRUCTIONS
Read these instructions
Follow all instructions
Keep these instructions. Do not discard.
Heed all warnings.
Only use attachments/accessories specified by the
manufacturer.
Power Cord and Plug
Do not tamper with the power cord or plug. These are
designed for your safety.
Do not remove Ground connections!
If the plug does not fit your AC outlet seek advice from
a qualified electrician.
Protect the power cord and plug from any physical
stress to avoid risk of electric shock.
Do not place heavy objects on the power cord. This
could cause electric shock or fire.
Cleaning
When required, either blow off dust from the product
or use a dry cloth.
Do not use any solvents such as Benzol or Alcohol.
For safety, keep product clean and free from dust.
Servicing
Refer all servicing to qualified service personnel only.
Do not perform any servicing other than those instructions contained within the User's Manual.
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PREFACE
Dear Customer:
Thanks for choosing LTOACL2 PRO 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 than 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 many 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 our work and our dreams with you, 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 ACL2 PRO 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 acquire an extremely efficient and universal dynamics
processor. It contains several new circuits design which make the unit an ultimate dynamic processor: intelligent
program recognition, Smart Expander/Gate and super low distortion VCA (Voltage Controlled Amplifier).
Nothing else to add, but that we would like to thank all the people that made the LTO ACL2 PRO 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
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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 Peak Limiter Section
3.4 Connectors on The Rear Panel
4. READY TO ROLL?.................................................................................................................................10
4.1 Expander/Gate Section
4.2 Compressor Section
4.3 Peak Limiter Section
5. INSTALLATION AND CONNECTION.....................................................................................................12
5.1 Mains Connection
5.2 Audio Connection
5.3 Rack Mounting
6. TECHNICAL SPECIFICATIONS ................................................................................................................................ 15
7. WARRANTY .............................................................................................................................................................. 17
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1. INTRODUCTION
You are now the Owner of an LTO ACL2 PRO Compressor/Limiter/Gate. The ACL2 PRO is a very powerful dynamic
processor. We have included in it with several innovative circuit designs that make the ACL2 PRO 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 ACL2 PRO includes 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 with User Adjustable attack and release time for the best total manual control.ACL2 PRO
Smart Ratio Control expander (SRC)
During music 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 expansion 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 Gain 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 theoutput signal
so that you will not hear any distortion. Smart, isn't it? The SGC proves to be very efficient in loud-speaker 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. 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!
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2.1.2 Introducing Audio Dynamics
The human ear can detect the noise generated 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 when dynamic capacity of various devices 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.
There is a very easy way to obtain this. With the volume knob in hand you can 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 during which the distortion and overloading will be generated in your audio equipment.
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 exceeds 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.
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