Pumping Drums

One cool trick is to create a super-funky “pumping” drum effect. What this effect basically does is to overuse an Audio Units compressor in such a way that it only allows the main body of each drum hit through before immediately clamping down and squelching the sound for a moment.Then the compressor enhances the quieter parts, emphasizing the quiet high-hat hits and the tail of the snare drum sound.

For this example I used the AUDynamicsProcessor, the loop Modern Rock Drums 02, and a tempo of 120 BPM. Here are some compressor settings to get you started (see Figure 1):

• Compression Threshold: -80 dB
• Head Room: 33.3 dB
• Expansion Ratio: 30
• Expansion Threshold: -87 dB
• Attack Time: 0.005 Secs
• Release Time: 0.087 Secs
• Master Gain: 6.0 dB

Figure 1: Starting settings for the “pumping drums” effect.

Play with the sliders to get the effect you want. The following guidelines will help:

• The Compression Threshold should be fairly low for the effect to work. However, if you set it too low you’ll squelch everything. At the same time, if you set it too high you won’t end up compressing anything and you won’t hear the effect.
• Head Room affects how “hard” the compression is. You probably want it fairly high or all you’ll hear are the initial attacks of each drum hit. You can almost set this slider visually—play with the slider while you watch the Comp Amount readout. If the entire bar consistently fills with blue you’re maxing out the compression—in other words, you aren’t giving yourself any headroom. I like to set it so the Comp Amount only fills about halfway.
• Expansion Ratio and Expansion Threshold are fairly enigmatic, and honestly, I’m not sure quite what they do. Suffice to say that if the Expansion Ratio is set to 1.00, it doesn’t seem to matter what you do with the threshold control. If the ratio is set relatively high, moving the threshold closer to zero can have some very strange repercussions. I generally set the ratio high and the threshold low and leave it at that.
• Set the Attack Time so you can hear it clamping down on the bass drum. If you set it too low, it will start compressing the initial attack, and the bass drum will sound a lot quieter. For the pumping effect, you want the attack to come through before the compressor kicks in.
• Set the Release Time fairly low. If you set it too high, you won’t get the “breathing” effect, especially noticeable in the high hat.

For even more control, you can use the AUMultibandCompressor to set different compression levels on different frequencies. This way you can compress the bass drum and the high-hat separately. For example, you may want the pumping effect on the bass drum only, leaving the high-hat more natural sounding.

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