There is not a lot of detail on the synth engines in Novation circuits beyond its two polysynthes. Connecting to components allows us to modify them in their entirety, however …
Circuit Tracks’ synths each have two oscs, offering a selection of virtual analog wavetables and wavetables. Index controls the pulse width of VA waves or the position of wavetables. Interpolation affects the transition through a wavetable when you adjust or modulate the index – at minimum setting the sound sweeps in increments and sharply, but at maximum the sound is much softer. Each osc has its own level control in the mixer section, where they are linked by a separate noise source.
Synchronize and detune
VSync creates a classic hard sync sound, but instead of syncing one oscillator to another, it uses an additional virtual oscillator, the setting of which is controlled by the VSync dial. Create classic sync sweep sounds by modulating them with an LFO or macro. The density works as a unison effect, creating duplicates of the wave. Use Detune to spread out the heights of these duplicated waves. In the mixer section we can also apply Ring Mod.
Each synth has a filter that can operate in low, high, and bandpass modes with two slope options for each. In addition to a standard resonance control for adjusting the peak level at the cutoff point, the Circuit filter has a Q parameter, which can change the width of this resonance peak. The filter also incorporates a multimode distortion effect, which offers the same range of drive patterns that you find on the main distortion, but works independently of that.
Modulation is provided by three ADSR envelopes, two LFOs and the eight macros. In the editor, modulation routes can be assigned by dragging a modulator onto an available control, or by using the Modulation Matrix tab. The list of available destinations is not as comprehensive as some digital synths, but each mod route can combine two inputs, which can have some interesting results. Each macro, on the other hand, can be routed to up to four destinations at a time, with varying depth and direction.
In the Effects tab, Circuit Tracks offers a main modulation effect – switchable between Phaser and Chorus – a three-band EQ and a main distortion. This distortion is largely the same as the filter control, but adds a compressor that can reduce the harshness of some distortion modes. Note that these effects work completely independently of the effects sends built into the tracks. This tab also allows us to control the polyphony and portamento / glide for our synth patch.