1. INTRODUCTION
You are now the Owner of an
ACL4 Quad Compressor/Limiter. The
is a very powerful dynamic
LTO
ACL4
processor.
We have included in it with several innovative circuit designs that make the
a very versatile
ACL4
processor: smart and
fast recognition of the program 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 can control the program
material so that the compression will be the most musical and inaudible. On the other hand, 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
Thanks to the AUTO function attack and release times of the program materials are automatically analysed in your
ACL4 unit. 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 Gain Control peak limiter (SGC)
4
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. 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!
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.
