In its purest sense, Compression basically allows you to reduce the gain spikes of a waveform. In Compressors Demystified, I addressed the three most common forms of Compression: Leveling, Transient, and Sustain compression. In this chapter we will discuss how compression is used in Sound Design, and specifically on drums.
CRUSH BUS (Extreme Leveling)
There is a common technique employed by engineers that utilizes a bus with sends from a drum kit. This Crush Bus allows the engineer to augment the sound of the original kit with a mix that on its own is quite lo-fi and squashed. Due to the nature of the heavy compression applied, much of the transient peaks are pushed-down, the waveform is "crushed", and as a result, you end-up with a blob of sustain. And it can sound quite awesome when combined back with the original source.
The Crush Bus will fatten your drum bus, add body to it. But more importantly, even though it may only be a minor addition compared to the overall drum bus level, this technique allows the engineer to make even the most boring drum kit sound supernatural. Just be careful of the additional gain. Adding-back an entire drum kit to the mix can create quite a gain boost.
Because you are essentially sending the entire drum kit to the Crush Bus and then attempting to control all transients, you will need a compressor with a fast attack so it can grab the transients before they are allowed through the compressor. Without a fast compressor, you will likely not be able to crush the transients, and when added back in the mix, you are going to be adding a lot of attack transients, which is not what you want from a crush bus.
As we discussed in Compressors Demystified, an 1176 style compressor would be optimal here. As we did with Leveling Compression, a fast attack and slower release are preferable. However, what may be different from normal Leveling Compression is the Threshold. Leveling Compression does not require a low Threshold, because you are only pushing 5-10dB through in order to even-out the peaks. For Crush Bus Compression, I recommend you start with a Leveling Compression design, but then reduce the Threshold even further until you achieve the sound you desire. What this does is tell the compressor you want you to compress way more of the signal than just 5-10dBs.
You may also find the Release can be decreased from standard leveling compression as well. In the example below, I dialed the Release to 100ms which gave the Crush Bus a good pumping action as you can see from the graph.
Recommended Compressor: 1176 - Logic Pro Vintage FET used here but really any 1176-style compressor should work
Threshold: ~-30dB
Ratio: 3-5:1 or more for extreme compression. I found beyond 4:1 in the Logic Pro 1176 didn't give me much if any more compression
Make-up Gain: I added ~16dB back to get to unity gain with my original signal. However, I also kept this bus about 10db lower compared to the parallel source
Attack: Fastest - You want to catch all of the transients
Release: Slow to Slowest - You may find the slower the Release the more your waveform is completely flattened. I prefer it to breathe a little.
Caution: This technique should be employed to taste and then mixed-back in with the original drums as an enhancement. Of course you can push a lot of it back into the mix, but you will find your overall drum gain may increase a ton, and your tone will suffer. There is a point of diminishing returns. I would recommend applying this technique as one of the first things you do to your mix because it has such a major impact on balance with other tracks.
PUNCH BUS (Sustain Compression)
Adding punch to a drum kit can be achieved with many different compressors and different applications. Some way better than others. Punch Bus uses a compressor in parallel that squashes the Sustain and leaves the Transient so it can be added back to the original drum bus. I call this Sustain Compression, but on a drum bus, in parallel, it can really help accentuate a somewhat ho-hum recording.
Notice here the transients are wide, they include a lot of sustain:
This is the same track with Sustain Compression. What you are trying to achieve is a more pronounced transient spike. Notice much of the width of the waveform is compressed:
When it comes to a Punch Bus, you may also want to exclude certain tracks like cymbals because their transients may become unwieldy. We probably do not need to enhance the transients of crashes or chinas. I usually only include kick, snare, and toms in my Punch Bus.
I also recommend you shape the sound with an EQ or dynamic EQ. You may find some frequencies added back to the mix with this method may become exaggerated easily, pulling them back with an EQ will tame them. With a Dynamic EQ, adding additional gain to frequencies that would otherwise make the original tracks somewhat muddy in the low mids or boomy in the lows may broaden the frequency footprint of your transients, making them stand-out even more.
I found the type of compressor I like best is an Optical (LA-2A style). If your compressor has attack and release, you will generally set Attack around 20ms which allows much of the punch from the drums to pass thru before compression kicks-in. You may also find an LA-2A or 3A (solid state version) works very well here with a fairly high Gain and Peak Reduction. But you should be cautious, the Release on the LA-2A is around 60ms, which may be too long depending on your source.
Setting Release properly on a Punch Bus depends on the amount of sustain you want to suppress and the tempo of the song. Too long, and you will start to compress transients as the release spills-over between hits. Too short and your sustain will pump back-out in the mix because the release will no longer control the compression. Watch your VU needle, if it doesn’t reset before the next drum hit, speed-up the release. Then, use your ears to ensure the VU meter is telling you the truth. You may have to increase the speed of Release even more.
Recommended Compressor: Optical - Logic Pro Vintage Opto or LA-2A or 3A
Threshold: ~-30dB - This pushes the compressor pretty hard so it grabs as much of the sustain as possible
Ratio: ~10-20:1 - The higher the ratio, the more Sustain you will limit
Make-up Gain: You may not need any here. Use the input/output meters as a reference, or simply dial it in to unity gain with your original source
Attack: ~20ms usually allows the Transients to get through before compression begins
Release: I set mine to about 100ms, but this may vary depending on the source
This is how I would dial-in my LA-3A to achieve a similar effect:
Be sure to adjust the HiFreq (side-chain high frequency filter) all the way clockwise (i.e., Flat), which means the compressor is not ignoring lower frequencies within its detection circuit. If you turn this knob counter-clockwise, it will bias only higher frequencies and anything below 1k will less likely trigger compression.
Note: Not all compressors act the same when it comes to instruments like a drum bus. Be sure to try whatever compressors you have and notice the difference. You may be surprised which ones actually sound the best.
ROOM BUS (Transient Compression)
While we aren’t exactly dealing with a room mic source here, you can alter the level of a drum’s sustain by employing Attack Compression to mimic a room mic. Again, because we are trying to suppress all transients, it requires a very fast compressor. Cymbals can be included in a Room Bus as well, but you may need a Dynamic EQ to tame whatever transient comes through that tend to overtake the Room Bus.
What you generally get with a Room Bus is the ability to augment, in parallel, the original source with something that sounds a lot like a room mic, although nothing can really replace a room mic. A room mic will usually pickup less transient because it is so far away. It will, however pickup a lot of the sustain as it tends to capture sound waves bouncing off the walls and objects within the room.
You can also enhance your Room Bus with a small amount of reverb. I typically use one that does not have a lot of size, distance, or feedback, like a large studio room. If used sparingly, this will make the Room Bus feel like a room mic, and when mixed back in parallel, add a lot of live feel back into the drum mix.
I really like the Hansa Studio+ IR (Medium Room) in Logic Pro. It is not only an awesome room, some would claim one of the best in the world, using the plugin in the chain after the compressor, I can mix-in dry and wet signals to taste. Notice here I have applied EQ to the reverb. This gets rid of low rumble and piercing high frequencies, and it is usually the curve I employ - or similar to it - for most my reverbs.
Recommended Compressor: 1176 - Logic Pro Vintage FET used here but really any 1176-style compressor should work
Threshold: ~-30dB
Ratio: 3-5:1 or more for extreme compression. I found beyond 4:1 in the Logic Pro 1176 didn't give me much if any more compression
Make-up Gain: I added ~16dB back to get to unity gain with my original signal. However, I also kept this bus about 10db lower compared to it parallel source
Attack: Fastest - You want to catch all of the transients
Release: ~20-50ms - You may find the slower the Release the more your sustain is compressed which is not what we are going for here.
CRASH BUS (Transient Compression)
Many times I feel my crash cymbals, whether they come from overhead mics or samples, have way too much transient. I generally go for cymbals that sizzle in a mix, not split your ears when they are struck.
Similar to the Room Bus, I may create a separate bus for my cymbals - usually this includes crashes and other loud cymbals with sustain, not hi-hats or ride bells. I suppress much of the transient so I can push-up the sustain of the cymbals in the mix. This achieves a couple things when used in parallel to your original source.
First, it allows you to increase the level on your crashes, chinas, etc. so they can compete within the mix without adding additional transients. Often I find I cannot wash my mix with cymbals unless I tame the transients quite a bit.
Second, you will find this may create a pumping effect if you solo the cymbals on their own, but if applied tastefully, in the greater mix, it can actually be quite musical and give your mix a lot of high-end sizzle and air that otherwise doesn’t exist. If you are really pushing a mix, this cymbal washing effect can be magical!
Similarly to the Room Bus, adding some reverb can also extend the sustain. But I will leave that for you to experiment.
When I learned this technique, I was amazed hardly any compressors could perform this effect. If you put a drum through the recommended configuration below it will sound really bad. But because the frequencies of cymbals are easily smashed, I was able to find a few that worked pretty well. My favorite of course is the 1176, nothing has a faster attack. But I was also intrigued the Comp VCA-65 by Arturia performed quite well under similar settings.
Recommended Compressor: 1176 - Logic Pro Studio FET shown above
Threshold: -50dB - This pushes the compressor pretty hard so it grabs as much of the transient as possible. Watch the graph as you move this up, you get less compression
Ratio: 30:1 - Reference the graph to see how the waveform is compressed. At this rate, you will achieve the maximum compression
Make-up Gain: ~20dB - You may find the Input and Output do not really match-up that well as they are reaching their peak (see above), but you will be able to balance the signal. Here I had ~-12dB on Input and Output at peak
Attack: Fastest - You want to grab all of the transient
Release: Fastest - Because most compressors don't release immediately, this will allow for a gentle re-entry of the sustain to the mix. Notice the stair-step in the graph as the compression releases
Here is what the Comp VCA-65 looked like. Notice the Time Warp setting, this impacts the transient even more:
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