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What is the difference between a compressor and a bus compressor ? And there is also mastering compressor..?

Ok, a compressor on a single track works on only one instrument, it must be 'easier' than on a bus. But a compressor is a compressor : it modulate the amplification thank to an envelope follower which doesn't 'know' if there is one or several instrument but 'sees' just a signal level in db, isn't it ?

I can understand there is some quality differences between all the compressors (there is so many on the market !) but I don't get the difference between bus comp, comp, mastering comp...

Any explaination are welcome !

Thanks !

optimaster i.e. has three bands, suited for a total mix.

Well, this is an another kind of compressor... But I understand the difference between a compressor and a multiband compressor !

The difference is at the function. The same compressor when is used in different stages of the mix has different names. You compress each instrument with a "compressor" (or a "channel" compressor), but you compress a group of signals by using your mixer busses with a "bus compressor" (or a group compressor). When you use a compressor at the mastering stage, well that compressor is named "mastering compressor".

There are times that a specific unit is tuned for a specific function * (rare) but it is common to use a general compressor and name it each time according to the different function it performs.
*For an example a mastering compressor can have less fast times because it's not common to make drastic changes to the sound at that stage. But that is not a rule. There are different ways to get the same sound treatment.

The same applies to compressor times. A compression function with fast attack/release times is named peak compression** with slow times, loudness compression.

** That depends also on how you analyze your signal. If you send the signal straight to the threshold detector its "peak", if you pass that through a envelope follower and then to the detector we have "rms".

JoPo wrote:Well, this is an another kind of compressor... But I understand the difference between a compressor and a multiband compressor !

sure, but I couldn't imagine the basic parameters of different compressors are purposely differently implemented.
Just didn't wanne make that statement, as I know nothing.
Fra77x seems to confirm my thought tho

yes, different compressors react a little differently. i have my favorites for specific purposes. experiment. use what you like.

I would have wished to know the technical detail which makes the difference...

would that make the music sound better?

most of the differences are in how the detector reads and reacts to the input signal.

http://www.soundonsound.com/sos/may08/a ... ession.htm
http://www.soundonsound.com/sos/sep09/a ... deeasy.htm

as a start...

as said before: different architecture, different results/applications. there are opto-compressors, FET-compressors, variable MU, VCA, digital...
all different, especially in envelope speed.

!! Thanks for the links !!

I take my dictionnary and go for studing..! It looks very interesting.

yes, that's right.
many different methods to measure the signal and then compress it accordingly.

i think the best wayt to learn about compressors is to actually play with a number of them, especially the ones that have been the most popular for radio, tv, stage and studio use from maybe 1960 on.

Of course a digital compressor can do it