There’s not much detail on the synth engines in Novation's Circuit Tracks beyond its two polysynths. Connecting to Components lets us edit them in full, though…
Circuit Tracks’ synths each have two oscs, offering a selection of virtual analogue waves and wavetables. Index controls the pulse width of the VA waves or the position of the wavetables. Interpolate affects the transition through a wavetable as you adjust or modulate Index – at minimum setting, sweeps sound stepped and abrupt, but at max sound far smoother. Each osc has its own level control in the mixer section, where they’re joined by a separate noise source.
Sync and detune
VSync creates a classic hard sync sound, but instead of syncing one oscillator to the other it uses an additional virtual oscillator, the tuning of which is controlled by the VSync dial. Create classic sync sweep sounds by modulating this with an LFO or Macro. Density works like a unison effect, creating duplicates of the wave. Use Detune to spread the pitches of these duplicated waves. Over in the mixer section we can also apply Ring Mod.
Each synth has a filter that can function in low-, high- and bandpass modes with two slope options for each. As well as a standard resonance control for adjusting the peak level at the cutoff point, Circuit’s filter has a Q parameter, which can alter the width of that resonant peak. The filter has a multi-mode distortion effect built into it too, which offers the same range of drive models as you find on the master distortion, but operates independently from that.
Modulation is provided by three ADSR envelopes, two LFOs and the eight Macros. In the editor, mod routings can be assigned by dragging a modulator onto an available control, or using the mod matrix tab. The list of available destinations isn’t as exhaustive as some digital synths, but each mod routing can combine two inputs, which can have interesting results. Each Macro, meanwhile, can be routed to up to four destinations at once, with varying depth and direction.
In the effects tab, Circuit Tracks offers a master modulation effect – switchable between Phaser and Chorus – a three-band EQ and a master distortion. This distortion is mostly identical to the filter drive, but does add a compressor that can reduce the harshness of some distortion modes. Note that these effects work entirely independently to Tracks’ onboard effect sends. This tab also lets us control polyphony and portamento/glide for our synth patch.