The text on this page is out of date and needs to be rewritten. Most tips are still valid, but clipping - which was added after this page was written - solves a lot of the problems described here, and the singleband compressor is no longer available.
This page describes how a good compression result can be achieved, without
common compression artifacts such as pumping, a flat sound and cracking sounds.
General considerations
In general, the following rules apply:
Use compression with care. Don't compress more than needed.
For the multiband compressor, this means keeping the Pre Amp at a low value.
For the singleband compressor, this means keeping the max amp slider at a low value.
When using the multiband compressor, try to keep the compression about equal
for all channels. If one frequency band is compressed a lot more than
the others, it will hurt the sound quality.
In Stereo Tool, this means
that the bars below the multiband sliders must on average be around
the same level.
Good
Bad
If they are not, adjust the soft limit to match the incoming
sounds, or use the Winamp equalizer to change the incoming signal.
(The default soft limit settings match the sound of
most modern CDs. Other sound sources may need different settings.)
If the goal is only to reduce some sudden peaks, use limiting rather than compression. Use a high up speed (.00010 - .00050) to avoid pumping.
Avoiding a flat sound
Compression often leads to a flat, powerless sound.
This is caused by the fact that when a loud peak arrives, the volume is turned
down immediately. If the volume rises again very quickly after the peak ends,
the peak itself is lowered to almost the same volume as the sounds surrounding it,
so it cannot be heard as a peak anymore. If this happens with drums etc., they
sound very weak.
There are several ways to avoid this:
Use compression with care. Don't compress more than needed. (See above).
Keep the up speed and/or the down speed low.
If the up speed is low (less than .00005), the volume won't have
risen a lot when the next drum kicks in, and the volume is not lowered
too much. So the peaks remain powerful.
Disadvantage: Output volume is lower, pumping can occur.
If the down speed is low (less than .025), the volume is not
lowered very fast when the next drum kicks in, and the volume is lowered
so slowly that the drum keeps its power.
Disadvantage: Sudden peaks are not completely removed. However, if this
happens using the multiband compressor, the singleband compressor can
still be used to remove the sudden peaks (see below).
In short, if both up speed and down speed are high, and the
input volume is high, this results in a very flat powerless sound.
Avoiding pumping
Compression often causes pumping; after a loud peak (for example a drum kick),
the volume is a lot lower, and starts coming back fast. If this happens too
slowly, especially if it's the singleband compressor that causes it, it can
lead to a very annoying sound.
The best way to avoid this is to use the multiband compressor for volume
levelling, and the singleband compressor to remove any remaining peaks.
There are several ways to avoid this:
Use compression with care. Don't compress more than needed. (See above).
Make sure that the compressors don't "dance" up and down too much.
In Stereo Tool, this means
that the bars below the multiband sliders should not move too much,
although setting the up speed at high enough values can mask
the pumping.
Also, don't set the down speed to a very high value (larger than 0.25)
if the up speed is not very high. This can cause extremely
short peaks to lower the volume a lot, which is usually unwanted.
Using the singleband compressor to remove remaining peaks from the multiband compressor
The singleband compressor can be used to remove remaining peaks that the
multiband compressor didn't remove. Especially when the multiband compressor
down speed values are low and the input volume is high, some loud
peaks can remain, which can be removed by the singleband compressor.
If only some short peaks remain, this is how to do it:
- Set the singleband compressor down delay to a very high value (.999 works very well).
- Set the singleband compressor soft limit to a very high value (above 95%).
- Set the singleband compressor up speed to a very high value (at least .000500).
- Set the singleband compressor compress/limit slider to limit.
- Next, set the singlebandcompressor max amp slider such that only the peaks that need to be removed cause the compressor to kick in. Turn DIFF on to hear the sounds that the compressor removes.
- Finally, set the the singleband compressor up speed slider just high enough to avoid pumping.
Note that the singleband compressor move so fast, that ugly artifacts can be
introduced. Therefore, it is important to make sure that there are not too
many peaks that are affected by this. On the other hand, setting the
soft limit higher does enable getting a louder playback volume, which
might also be useful for some purposes.
Examples
See the VOLUME COMPRESSION presets in Stereo Tool for a number of example
compression settings.
