[sdiy] Waveform phases and hard sync, sawtooth vs. triangle?

Mattias Rickardsson mr at analogue.org
Thu Jun 21 16:07:54 CEST 2018


is there any general consensus or preferred design choices regarding how
the phase of sawtooth waves and triangle waves should align with each other
and with oscillator sync?
I'm sure that there are many sides of it, but for a saw core it feels like:

- The normal way of syncing/resetting a saw core is to restart the saw from
its endpoint

- The tri/sine waveforms are then created by folding the saw in half

This results in a synced tri/sine restarting from one of its peaks, leading
to maximum discontinuity click which I guess must be considered undesired
for the majority of usecases. The attack of a tri/sine-based drum sound or
synth sound should probably start from a zero crossing. This could be
reached in a couple of ways:

- Is it really desired (from a usability perspective, not a circuit design
perspective) to have the synced sawtooth restart from the endpoint and not
the midpoint or quarter points? Does it matter in terms of direct sound or
audio-rate modulation?
An alternative restart point for the sawtooth would facilitate a triangle
restart from a zero crossing without having to change the traditional phase
alignment of saw & tri.

- Is it really desired (again from a usability perspective, not a circuit
design perspective) to have the triangle peaks phase aligned with the
endpoints and midpoints of the sawtooth? Does it make more sense
considering the phase of the harmonics in case of waveform mixing?
An alternative alignment would be to have the triangle's zero crossings
there instead of its peaks. This would mean that the oscillator, when
synced, starts the sawtooth from its endpoint (traditional) but the
triangle from the middle (new).

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