The Basics

The bass guitar and kick drum have common traits which can work together to achieve a powerful musical result. Often unnoticed, these similarities sometimes compete and interfere with each other, muddy the mix, confuse the listener, and reduce the power of the musical experience.

The first and perhaps most obvious of these common traits is their fundamental frequency range: LOW. The bass guitar's fundamental tones and most interesting overtones include frequencies from about 60 Hz up to about 1 KHz. The residual noise after a kick drum hit can cover a band of frequencies from below 20 Hz to about 100 Hz. I think of the kick's sound as having two parts: an initial attack which covers a broad band of frequencies from 100 Hz. to 15 KHz. followed by a (pitchless) decay in the 20 Hz to 100 Hz range. It is the second 'part' of the kick's sound which competes with the bass guitar.

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	Figure 1. A three-axis plot showing the decay of the typical kick-drum sound energy over time, by octave band. Note that the attack is present across the whole spectrum (in reality it depends on the hardness of the beater), so that the kick drum should be thought of as a broad spectrum sound. Note also that the low frequencies can sustain. In practice, they are often damped, in order to cut off that sustain, shortening the sound down to perhaps as little as 250 ms.

One goal of mixing is to use as much of the frequency spectrum as appropriate for the musical style being mixed. At the same time, there should be comparatively little frequency overlap. This is particularly true for the low frequencies of the bass guitar and kick drum. Typically, equalization adjustments are made to insure the fundamental spectrum of the kick drum is beneath the bass guitar. However the broad band of frequencies associated with the drum's 'kick', the attack, should not be removed. In fact, they probably should be boosted somewhat, so that spectra into the 10th octave (16 KHz) is encountered as part of the attack. This permits the kick drum to be a forceful element even on tiny speakers such as Auratones and their ilk. In the lower octaves, the drum's punch must be maintained, but there should be plenty of space left, in both frequency and time, for the bass. While the fundamental of the kick drum lies between about 40 to 100 Hz, these are, fortunately, not the critical elements of the electric bass spectra. Instead, it is the overtones in the fifth and sixth octaves (300 to 1200 Hertz) that are especially important in defining the pitch character of the bass. Reach for these when mixing. Careful equalization can separate the two instruments in the frequency domain and give them independence while preserving their harmonic and rhythmic identities.

Second, just as bass guitar and kick drum sometimes occupy the same frequencies, they also occupy the same stereo position in the mix: DEAD CENTER. There is (or rather, was) a technical reason for this: on vinyl discs* the low frequency information contained in these two instruments had to be mono to keep the stylus from jumping out of the groove -- this technical constraint has now become an element of style. At the same time, the harmonic foundation and rhythmic pulse provided by these two instruments is critical musical information: they are the nucleus about which all other musical activity revolves, and they belong in the center of the sound stage. However, we cannot allow conflict or confusion in this area of overlap. If both instruments are to reside in center stage, they must complement, support and make space for each other. The drummer can give the bassist space in time and allow the bass to play for a beat, a measure or several bars without competition from the kick drum. Likewise, the bassist can leave room for the drummer. When the bass guitar and kick drum are to coincide, they must do so with precision. A sloppy time feel in bass or drums will immediately be noticed. In addition to the musical weakness this creates, in multitrack music it clutters the middle of the mix thereby weakening the impact and power of this harmonic and rhythmic nucleus. The resulting tape is no fun to listen to and hard to sell.

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