Anatomy of a kick drum
A physical kick drum – or bass drum – is made up of a wooden shell with a typical diameter of between 22 and 26 inches, and a stretched head (or skin) that is struck by a beater held in a foot pedal. Depending on the musical style, there may also be a front head, the skin on which you’ll see a band’s name. This skin is commonly punctured with a small hole for a couple of reasons: it allows air to escape and reduces the tail of the sound, and it allows the engineer to insert a microphone and damping materials.
The tone of the drum is dependent on many things, most obviously the construction, the diameter, the tuning of the skin, the type of skin, the damping inside the drum, the nature of the beater and so on.
The kick sound itself can be broken down into the ‘front’ and the ‘tail’. The front is the attack portion of the sound, the initial transient, which gives the ‘smack’ and cuts through the mix. It’s generally bright in tone from the impact of the beater on the skin and only lasts a few milliseconds. A wooden beater will give you a really bright and hard front, while a woollen or cloth beater will be very soft and probably wouldn’t be strong enough to cut through a busy mix – although it might sound good on a spacious, slow track. A good compromise is a leather beater, which gives a good amount of warmer transient with a thicker tone.
The tail of the sound is the natural low frequency resonance of the shell as the sound decays and gives you the deep pitch of the drum sound. Lugs around the rim are used to tighten or loosen the stretch of the skin to raise or lower the pitch respectively. It’s important to get an even tension at each lug point in order not to create dissonant rings within the sound and also to find a sympathetic tuning of both skins for a similar reason, especially when you’re going for a longer decay. Tuning the kick should therefore as much as possible be done in context of the track you’re recording.
The length of the tail is as important if not more so than the pitch, and the decision is dependent on the tempo, the arrangement complexity and the accompanying bass part. A down-tempo track with a sparse bassline can probably afford a long decay, whereas a fast song with a busy arrangement will have little space for a ringing kick and will require a tight, punchy sound with a short decay. This is where skilled damping comes into play, filling the inner shell with cushions or weighting a pillow against the front head, and using duct taping over tissue paper at specific points on the skin to kill off unwanted dissonant rings.
Synth kicks
With knowledge of the anatomy of the kick, it’s possible to synthesise the elements and manipulate the attack and tail to suit the track you’re working on. Getting the tuning of the boom is essentially easier than on a real kick because you can match the pitch oscillator to the key of the song and marry it to the bass sound. Its tail length you can control from an amplitude envelope using the decay knob. The brightness and hence cut of the transient can be controlled using the attack of a filter envelope. The beauty of a custom-made kick sound is that it’s unique and tailored to your track, rather than an off-the-shelf version that’s square-pegged into the role.
Sampled kicks
Covering both real and synth kicks, a sampled kick has the advantage of being constant in both level and timing, which in many cases is what you’re after, particularly in dance music. A typical real drummer never hits the kick with the same purpose, and often tires towards the end of a take. A good pro session drummer, however, will be consistent and also add accents which will have a natural filter to the transient and give you a human feel to the timing, which in certain circumstances is desirable. And there’s always a compressor to even out the levels and give some added punch.