Differences between compressors

[JoPo]

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 !

[hubird]

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

[JoPo]

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

[fra77x]

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".

[hubird]

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

[garyb]

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

[JoPo]

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

[garyb]

would that make the music sound better?

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

[borg]

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.

[JoPo]

!! Thanks for the links !!

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

[garyb]

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.

[fra77x]

Of course a digital compressor can do it