So mystical ninja, it's perfectly true that a compressor would help "bring out the lows" in vocals if the highs were too loud, i.e. if the chunks of time during which was the vocal was high were louder than the ones during which it was low, since the gain would be decreased on the high parts more than on the low ones. But it is also true, as Sanguis Mortuum said, that in the parts of a song where the compressor lowers the gain, all frequencies are lowered equally.

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All a regular (digital, non-multiband) compressor does is lower the gain when the threshhold loudness is reached.

It doesn't just lower the gain, it only lowers the gain of the signal that is above the threshold. So, if only the high frequencies are passing the threshold, only the high frequencies are compressed, thus all frequencies are not lowered in gain equally.

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Last edited by mysticalninja on Aug-03-2007 at 05:30

hi all, first post, so go easy on me...


I'm pretty sure that mystical ninja is right, as that is how it is possible to raise the 'noise floor' or noise underneath the samples through compression. As it chops the tops off your peaks, you can turn up the signal, bringing up the lower level signal that doesnt touch the threshhold , also bringing up with it the 'noise floor'. Hope this makes sense...

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Originally posted by mysticalninja It doesn't just lower the gain, it only lowers the gain of the signal that is above the threshold.

Yes, "signal" meaning the whole stream of audio. A normal compressor does not detect which frequency ranges are passing the threshhold (that's what a multiband compressor does). All it detects is whether the audio signal as a whole is passing the threshhold, and once the signal passes the threshhold, it lowers the gain on the whole signal.

In order apply to gain separately to different frequency ranges, you have to split one signal into two or more signals. A normal compressor does not do this. All it does is detect and control the level of a single audio signal:

"A compressor accomplishes its task of reducing dynamic range by using a variable-gain amplifier to reduce the gain of the signal. This is typically carried out in analog systems by using a voltage controlled amplifier which has its gain reduced as the power of the input signal increases."

http://en.wikipedia.org/wiki/Audio_...ion#Explanation

That is all a normal compressor measures and modulates: the power of a single audio signal. It does not act differently on different frequency bands within the same stretch of time; that's what a multiband compressor is for.

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Most of the compressors we use in music production operate on what is known as the full-band principle, where the entire audio signal is processed via a single gain-control element. When gain reduction occurs, the whole signal level is reduced, just like turning down a volume control. In other words, whenever a loud peak occurs (whatever its frequency content) that forces the compressor to act and the level of the whole signal is reduced until the loud event has passed. A common problem arising from this method of compression is that a loud kick drum (which produces mainly low frequencies), will trigger the compressor and consequently pull down the gain of everything else that happens to be passing through the compressor at the time, even though those other sounds might not need compressing. ... The main advantage of multi-band compression [as opposed to normal, full-band compression] is that a loud event in one frequency band won't trigger gain reduction in the other bands [as it would in normal compression], so when that loud kick drum comes along, instead of pulling the whole mix down with it, only the low-frequency sounds (kick and bass instrument) will be compressed, leaving the mid-range and high frequencies untroubled.

http://www.soundonsound.com/sos/aug...s/multiband.asp

Case closed.

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Originally posted by mysticalninja It doesn't just lower the gain, it only lowers the gain of the signal that is above the threshold. So, if only the high frequencies are passing the threshold, only the high frequencies are compressed, thus all frequencies are not lowered in gain equally.

NO. What you're describing is a multiband compressor. You clearly dont have the slightest clue how a compressor works...

Ah sorry MrBoJangles I confused you.. wrong choice of words on my part.

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Originally posted by Sanguis Mortuum NO. What you're describing is a multiband compressor. You clearly dont have the slightest clue how a compressor works...

Ok, 'only the high frequencies are compressed' is wrong, that is only possible with a multiband compressor, you are correct. What I ment to say, is only the signal above the threshold is reduced in gain, which may happen to only be the high frequencies in a sound, but yes, technically all the frequencies in the signal above the threshold are being reduced.

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Most of the compressors we use in music production operate on what is known as the full-band principle, where the entire audio signal is processed via a single gain-control element. When gain reduction occurs, the whole signal level is reduced, just like turning down a volume control. In other words, whenever a loud peak occurs (whatever its frequency content) that forces the compressor to act and the level of the whole signal is reduced until the loud event has passed.

Yes, the whole signal above the threshold that is. Think about it, if the entire signal was reduced when the threshold is passed, it wouldn't change the dynamics at all, would it?



This is what makes it different from a triggerable volume knob.

This next little gem you quoted proves my point.

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The main advantage of multi-band compression [as opposed to normal, full-band compression] is that a loud event in one frequency band won't trigger gain reduction in the other bands [as it would in normal compression]

In normal compression a single loud event in one frequency will reduce the gain for all signal above the threshold, it does not need to detect frequencies to do this.

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Last edited by mysticalninja on Aug-03-2007 at 09:01

Let's say you have two sine waves going on at the same time. One of them, the higher one, goes above the threshhold for a short bit. A normal compressor will reduce the gain on both of the sine waves for as long as the louder wave goes above the threshhold.] When gain reduction is used on a normal compressor, it is used on all frequencies at once. That is the point made in the article I quoted. The author says that, for example, you might have a kick that's above the threshhold. In normal compression, if you have a compressor on the master, everything else that's happening at the same time as the kick will also be reduced in volume: vocals, hi hats, synths, whatever. This is why you get that "pumping" effect if you use too much compression on the master bus. The whole song "pumps" in and out, pulsing with the kick that's causing the compressor to reduce the gain.

Hopefully this is clear now...

Last edited by MrJiveBoJingles on Aug-03-2007 at 10:06

Whilst the thread has gone a little off topic, it has been an interesting read. However, I'm glad that Mrjivebojingles has stepped in and explained exactly how a compressor works because this is the same as I have been taught and when Mysticalninja and richg pushed the idea of a compressor only affecting certain frequencies, I began to question if I ever understood a compressor in the first place.

Are we in agreement now that a normal compressor compresses the entire signal, not just the frequency that steps over?

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Originally posted by G-Con Are we in agreement now that a normal compressor compresses the entire signal, not just the frequency that steps over?

Yes we are all in agreement of that.

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Mysticalninja and richg pushed the idea of a compressor only affecting certain frequencies

That's not even close to what we said at all.

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Last edited by mysticalninja on Aug-31-2007 at 06:32

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Originally posted by mysticalninja Yes we are all in agreement of that.

Good, thats all that I was trying to say really...it certainly didnt sound like you agreed though with your statements like "So, if only the high frequencies are passing the threshold, only the high frequencies are compressed, thus all frequencies are not lowered in gain equally."...

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Originally posted by Sanguis Mortuum Good, thats all that I was trying to say really...it certainly didnt sound like you agreed though with your statements like "So, if only the high frequencies are passing the threshold, only the high frequencies are compressed, thus all frequencies are not lowered in gain equally."...

I know I really didn't mean to say that.

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