The snare drum playing of even the best drummer will vary in level. Compression can help to make the level more even throughout the song.
Here's a snare drum that varies in level (video clips will be best viewed in full screen mode)...
In a full song arrangement, the variation in level will make the snare difficult to mix. Some hits will be too loud, some will be too quiet.
So it is useful to be able to even out the level. This can be done using automation, but here we will do it with compression.
Settings have already been chosen that work well with this snare drum. Clearly the settings will differ according to the requirements of the recording, so you should consider that these settings relate only to this recording of this snare drum.
To explain the settings...
Let's hear the snare drum uncompressed again...
The purpose of compression here is to even out the level.
A compressor works by bringing down the level of high-level signals. For this application there is no point in reducing the level of the quietest drum hit. It's quiet, possibly too quiet, already.
So we need to set the threshold level such that the quietest drum hit is not compressed.
We can see this in the gain reduction meter. In this compressor you will see two indicators in the gain reduction meter, labelled GR. One is an easily visible yellow bar extending vertically downwards, showing by how many decibels the signal level is reduced from moment to moment.
However in this compressor the vertical yellow bar can be a little slow. It's good for indicating the subjective amount of compression, but not the exact amount. Here we would prefer to know the exact amount of compression.
In this compressor the exact gain reduction is more accurately indicated by a thin yellow horizontal bar with a fast rise-time and slow fall-time. It's hard to see unless you're looking for it. But the click effect in the video below will guide your attention.
What we want is for the quietest hit not to be compressed. The video clip below shows that with a threshold of -12 dB, the quietest hit is compressed. However if the threshold is raised to -11 dB it is not compressed, at least not according to the meter but we will trust it.
This shows that we have found the correct threshold setting. Any lower would compress the quietest hit. Any higher would not compress all of the hits that are higher in level than the quietest hit.
Now that we have found the right settings, the compressed snare drum sounds like this...
And for comparison, with the plug-in deactivated.
The difference might be difficult to hear on first listening, but there is a further demonstration that will make it extremely easy to hear the difference.
For this, the compressed snare drum is placed in the left channel; an uncompressed copy is placed in the right channel. If you listen on headphones you will hear more clearly that the right channel varies in level much more so than the left. Of course you wouldn't use it this way, but it's an interesting demonstration.
Compression can be very useful for evening out the level of a snare drum. If the aim is to retain the natural sound of the drum, then appropriate settings must be found by experiment, and the threshold set so that only the hits that are louder than the quietest hit are compressed. Following that, the fader level should be set so that the snare drum sounds at the right level in the context of the full drum set, and in the context of the complete mix.
For this example we are talking about full-on drum strikes not ghost notes. You should ignore any ghost notes when setting the threshold.
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