I'm having trouble with a synth bass sound I've been using in a song. It sounds impressive on its own, but isn't working so well in my mix, and never seems to punch through enough. I've tried applying EQ to get it to stand out more, but it either gets too boomy and muddy or harsh. When I raise the level, the lower notes become too dominant in the mix, but compressing them kills the sound. Is it my EQ technique, or is there a problem with using synth bass sounds?
Chris Piconzeh
SOS contributor Tom Flint replies: It may be the case that the sound can be improved with the right kind of EQ, a well-adjusted compressor and even a little reverb, but it's probably best if you tackle the problem at source: the sound itself.
If the selected bass sound is pleasingly impressive without accompaniment, it is probably because it was programmed to stand out in that way, but that doesn't mean that it is ideal for use within a composition. However, you may be able to adapt it to work better in the song without changing its character drastically.
Many synth parameters are scale-sensitive, and their programming will suit certain areas of the keyboard, so the first thing to work out is the keyboard range that the bass line occupies. As you probably know, on a piano each octave is given a number, and middle 'C' is at the start of the fourth octave, giving it a value of C4. Most bass lines are played an octave or two below this centre point and, while some specific bass sounds will be optimised for the range, others will not. If a sequencer was used for programming the bass, a quick glance at the MIDI data will show the range of the notes, otherwise the synth manual should show the un-transposed value of the keys.
Once you know the bass range, you can edit the parameters accordingly. How easy this is will depend on the synth, and whether the sound is based on a waveform or sample. Nevertheless, as long as there are a few editable oscillators, envelopes, and filters, some significant improvements should be possible.
A common pitch-envelope parameter called Key Follow enables the programmer to change the pitch of a note as it moves away from middle C, up and down the scale. Normally a synth program will have equal temperament, meaning that its pitch will rise, or fall, an octave with every 12 notes of the keyboard. But some sounds are programmed away from the standard for effect, which won't necessarily benefit a bass played two octaves lower than intended. On Roland's S&S (sample and synthesis) synth models, for example, a Tone can be made from up to four parts (Partials), which are often set with differing tuning parameters to give the overall sound more character. Adjusting them to similar values is one way to improve the tonal focus of a bass line.
The sound's pitch envelope may also need adapting. When a note on a bass guitar is plucked, its pitch is likely to vary as the string is stretched by finger or pick, and the programmer may have tried to reflect this in the design of the envelope. Changing the speed, depth and shape of the envelope to suit the performance can often make the bass more convincing. Similarly, changes to the amplifier and filter envelopes can also ensure that the sound peaks and falls away appropriately, further emphasising the note.
One trick to use when using a sound program comprising several Partials is to make the pitch of one of the Partials an octave higher than the other. This higher Partial can then be lowered in level relative to the others, so that it subtly gives the sound a little more presence where the ear is slightly more sensitive.
Filter envelope cutoff frequencies are used to affect the brightness of notes in certain areas of the keyboard. By adjusting frequency Key Follow, you can change the action of the cutoff filter to suit the bass.
Although it's tempting to make the sound brighter, so that it stands out more, doing so can have the effect of making the bass noisy, causing it to compete with vocals and guitars in the mix. A more muted bass sound is often a better choice, as it can be made louder in the mix without interfering with sounds further up the frequency spectrum.
As mentioned earlier, programmers love to detune Partials or oscillators to give sounds a thickening chorus effect, which can sometimes cause bass sounds to feel off-key, but I've also experienced problems with bass sounds that use two identical waveforms programmed to have different envelope dynamics, causing some notes to be cancelled out and others to be doubled up. Make sure that none of these programming tricks are damaging the effect of the bass.
Low bass notes tend to become boomy and can often cause problems during the mix, as they can dominate the track and trigger buss compressors. Mastering engineers will try to attenuate low bass through the application of shelving EQ filters and compression, but their actions can potentially compromise other elements within the track.
Key tracking can also be applied to amplifier envelopes, and some digital synths offer the ability to adjust key tracking only below or above certain notes. Roland call these settings Bias Points, whereas Korg use the term Keyboard Tracking, but they are essentially the same. If one or more Partials are becoming too prominent at the bottom of the note range, try setting their Bias Points just above the problem notes and then creating a gentle negative slope. This is a subtle way of controlling the low end which allows the overall level of the bass to be increased without making the low notes boom or dominate the mix. Another thing that's worth trying is reducing the velocity sensitivity of the amplifier envelope so that harder-hit notes don't stand out so much. This reduces the dynamic range of the bass, meaning that less compression is required, and can be used for musical reasons rather than to keep it under control.
Finally, when you have your bass tuned, try recording it in mono rather than stereo, like most synth sounds tend to be. Due to the physics of the human head, we are unable to detect the stereo positioning of frequencies under 100Hz or thereabouts. There is, therefore, little point in using two channels, when having a centrally panned mono sound will help to focus the bass.