User`s manual

Chart.1: The dynamic range capabilities of various devices

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

2.1.3 More technical stuff about Compressor/Limiter

Clipping Signal heavily distrortedClipping Signal heavily distrorted

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

Clipping Aera

Noise Aera

2.1.4 More about noise: Expanders and Noise-Gates

certain "reserve" must be maintained to avoid distortion. This reserve is known as "headroom" and it is us-

ually set at 10-20dB. Would it 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.

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 sig-

nal peaks and consequently levelling them out. Manual control is therefore out of the 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".

A lot of instruments such as microphones, amplifiers, guitar pickups, etc. generate some noise, either at low

frequencies (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.

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/Limiter will be used. Both compressor and limiter more or less do the same

job but limiter brutally limits the audio signal above a set threshold, while compressor 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 fun-

ction 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 to the amount above the set threshold.