After 20 years as a college professor, I’ve noticed a few recurring misunderstandings about the details of synthesis: And as a preset designer, I’m occasionally surprised by sounds that make it through the curating process. This month, I’ll address five common synthesizer features and offer a few ways to ensure that you’re using them with intent in your own original presets.
Fig. 1. Setting a pair of fine-tuning controls equally in opposition directions keeps your patches from sounding out of tune with other instruments.
While some dual-oscillator vintage synths only allow fine-tuning of one oscillator, many modern synths—both hardware and software—allow independent tuning of both oscillators. Even so, I encounter presets that feature positive-or negative-only detuning on one or more oscillators. This is a no-no because it means that those patches will always be slightly sharp or flat (respectively) and, thus, will not be in tune with other instruments.
When you are detuning a multi-oscillator patch, always set the fine-tuning to equal amounts in opposite directions (see Figure 1), if possible. This will keep your presets in tune with other instruments in a track.
MISMATCHED RELEASE TIMES
When working with both filter and amp envelopes (or modulator and carrier envelopes in FM synthesis), it is crucial to ensure that the release time of the filter or modulator envelope matches or exceeds the release time of the amp or carrier envelope. If it’s too short, there will be a sudden jump in timbre as you release the key. Sometimes this is desirable, but more often than not, it can be confusing for newcomers.
UNDERSTANDING INVERTED ENVELOPES
Fig. 2. A graphic example of an inverted 4-stage envelope controlling the cut-off frequency of a filter.
Inverted filter envelopes are a powerful tool for simulating horn swells and other exotic tricks. However, the key to using them correctly is understanding that, unlike positive envelopes, negative envelopes subtract from the base value of the cutoff frequency or other modulated parameters. Accordingly, their sound is that of an instant attack followed by a variable decay (the attack segment) until it hits “bottom” (determined by the negative envelope amount). At that point, it rises (based on the decay time) until it reaches the sustain level, where it remains until the key is released, and then it returns to the original value of the cutoff frequency. Though this may sound confusing, Figure 2 is a clear diagram of what’s actually happening.
FILTERS ON SINE OR TRIANGLE WAVES
Sine waves contain a single fundamental frequency, whereas triangle waves offer an attenuated set of odd harmonics. As a result, adjusting the cutoff frequency of your filter has a negligible effect on those waveforms; in the case of a sine wave, the filter functions as an imprecise volume control and nothing more.
While sines and triangles are great for supporting brighter waves, on their own, filtering them is generally unnecessary.
UNDERSTANDING KEYBOARD TRACKING
Positive keyboard tracking increases the filter’s cutoff frequency as higher notes are played. Negative keyboard tracking does the opposite. Most often this is used to keep the relative brightness of a patch consistent across the keyboard.
But with high resonances, it can also be used to tune a filter directly for use as an additional pitched element or peak in the frequency range.
To set this up, use a sawtooth waveform with high resonance and 100% keyboard tracking, then adjust the cutoff frequency until the fundamental pitch of the oscillator pops out. It may require some experimentation, but mastering this tool is a great way to use the filter as an additional oscillator, as it can be used to emphasize any harmonic present in the original signal.