How to Compress Drums
by Katie Gilchrest
The sound of modern drums in rock, pop, and electronic music very rarely embodies the natural range that acoustic drums are capable of. This is most often due to the application of compression, adding punchiness, energy and consistency to a drum track. Compression can be added to each individual drum, even cymbals, and over the whole kit. The amount and perimeters depends on the sensibility and genre the engineer and songwriters are going for. Whether using hardware or software, most compressors have the same functions. This article gives a helpful overview for general uses and guidelines on how to compress drums.
The Threshold sets the level at which the compressor starts working. Peaks above the threshold are the only parts of the signal that will get compressed.
Signal below the threshold signal is unchanged. Anywhere from -10dB to -15dB is a good place to start with drum tracks.
The Ratio parameter indicates the amount of attenuation applied to the signal. In terms of decibels, a ratio of 2:1 means that a 2dB change in input level results in 1dB change in output level. Most of the time in modern music, each individual drum piece is kept at a fixed level. For electronic drums, the hits are usually fixed and consistent to begin with, but additional compression and modifications can be made to your liking. Starting ratio points should be made around 4:1 to 6:1 for each drum or cymbal. This is also a good starting point for the overall kit while learning how to compress drums.
The attack time is the amount of time the compressor takes to react to a signal that has exceeded the threshold. Depending on the time, you can change the sound significantly, and add punch and energy. Percussive impact can be important with drum tones, and you may want to allow the first transient sound through with a slow attack time. When the first edge of the beat is allowed through at full level before the gain is pulled down by the attack time, a punchy sound is created.The initial click of a cymbal or drum, especially the hi-hat and bass drum, can add authority and liveliness. Slow times range from 10 milliseconds (ms) to 100ms, with faster times <10ms.
Release time is the amount of time the signal returns to its normal, uncompressed state. A short release time can be manipulated to add pumping and “breathiness” to the sound as the amplitude rapidly changes. Longer than attack times, release times are usually between 30-60ms, but can go up to 5 seconds. Between 20 and 100ms is a good place to start. Some engineers prefer to set the release time just after the pumping becomes inaudible, although pumping is frequently a desirable phenomenon. Short release times over the entire kit make for the breathing factor, as the compressor might be working to recover from the short, dominant sound of the kick drum.
The Knee sets the transition character between the compressed and non-compressed signal. Certain compressors offer a choice between a “hard” knee and a “soft” knee. A soft knee describes a more gradual transition, sounding smoother and less severe than a hard knee. The human ear may not notice the progressive nature of the soft knee, but might pick up on the aggressive change due to the hard knee. The choice of the hard or soft knee is up to style and taste. A range between the two is ideal in order to sculpt the right transition between compressed and non-compressed. Many engineers prefer a hard knee for percussion, since the sounds are more transient like in nature anyway, and less noticeable with a hard knee.
Also known as makeup Gain, compressors effectively reduce the loudest part of the signal to the softest part of the signal. Even though it sounds subjectively louder, the signal is attenuated. To make up for this attenuation, Output Gain can be applied. When a gain reduction meter is visible, the exact dB is shown and you can add the right amount of gain.
Using compression correctly can add polish and excitement to a mix, but too much may render music lifeless. Another undesired effect of compression could be fatigue, in which your ears may get tired and you may not want to finish listening to a track. Use good taste and judgment while learning how to compress drums. Reference tracks within your chosen genre, and ultimately trust your own ears.
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