Elektron Musical Instruments

"Compressors are the last thing you need to learn,
IMO.. If you can mix
properly without, you'll make a much better sound when
you start using
them. Their primary use for making music is to change
dynamics for fun
- not for loudness"
Excuse me, but I would like to correct something about
compressors...
They were'nt designed for fun, they do exist because
NO audio system (not even one) is able to handle the
full dynamic range of real world sounds.
The theorical dynamic range of a 16 bit converter is
about 96dB. A 24 bit converter has about 130 dB of
theorical dynamic room. You can easily forget 15 dB
when it comes to reality.
An analog mixer or tape recorder rarely have more than
110 dB of dynamic range.
Real world sounds can exceed 140 dB: a full symphonic
orchestra playing pianissimo or a jet take off, for
example.
The idea behind compressor is very simple:
  they just lower the signal level above the threshold
in a non linear way, such as it fits the dynamic
"window" (or capacity) of an audio device.
Example:
-If you want to record an audio program on a tape, you
have to search it's maximum level and adjust the
recorder's input sensitivity so that there's no
clipping.
-If there's only one peak in the program, you'll have
to reduce the overall gain, which is a shame.
-If you use a compressor, you'll then be able to
reduce this peak (with a ratio of say, 3:1, the signal
gain only 1 dB after comp for 3 dB more at the input
when the threshold is exceeded) with the benefit of
being able to record your whole program louder (the
peaks have been reduced).
More simple:
-Under the threshold
Compressor input -30 dB (for example)
Compressor output -30 dB
Above the threshold (Ratio 4:1)
Compressor input +12 db over Threshold
Compressor output +3 dB.

If you want to know what is the sound of heavy
compressed signals, just listen big FM Radios: compare
the sound of a well known song
A on the radio
B your own record at home

Short: heavy compressed sounds loose their life (a big
block of sound) but well used, a compressor is the
sound engineer's swiss knife.
Hope this helps...

Sylvain,
Electronic engineer at Radio France, Paris.


	

	
		
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