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

[Mattias Rickardsson]

On Fri, 22 Jun 2018 at 03:59, <rsdio at audiobanshee.com> wrote:

> 1) Why do you think that starting from the midpoint will be any less of a
> discontinuity than starting from a peak?
>
> The discontinuity amplitude would be 6 dB less, on average, but it’s still
> a discontinuity that can vary from cycle to cycle (at least when modulating
> pitch of one VCO).
>

Well, it is less then. ;-)

I was keeping the questions a bit open, but I'm also aiming for the other
even more important application of sync: Restarting oscillators at note-on.
When you make drum synthesis, FM synthesis or even some regular bass
sounds, it's often important that the oscillator(s) behaves identically
each time the sound is started. (Note that this is with un-synced,
free-running oscillators after the start sync pulse.)

Starting from silence, then starting playing a sound with short attack,
using triangle or sine wave, it's definitely not desirable to start with a
discontinuity to the peak of the wave. You need a way to start the tri/sin
at the zero crossing.


> 2) Are you looking to create vintage sounds or new and unique sounds?
>
> If you’re shooting for vintage, then the circuit design perspective will
> cover the most cases.
> If you’re looking for new and unique sounds, then I say that it doesn’t
> matter what the general consensus might be - just offer options between
> simple circuits and more complex circuits so that more sonic variation is
> possible.
>

I'm looking to create all sounds. :-) Percussive sounds, drum sounds, synth
sounds of old and new. I'm personally not a huge fan of classic sync leads
and similar, but I still consider sync an important feature - both between
oscillators and at the start of a sound. And since I consider it important
to sync a triangle at its zero crossing, where the sawtooth wave normally
is between its peak and its zero crossing, I'm wondering how important the
sync start point of the sawtooth wave is in people's opinions.


> 3) Of the three standard waveforms - square, saw, triangle - two of them
> have significant discontinuities. Triangle is the exception. It seems to me
> that discontinuities in the triangle waveform when using sync will simply
> put the triangle back into the majority category.
>

Yes, and that kind of makes it lose its potential of being the mellow one
of the standard waveforms.


> For me, the best part of turning on hard sync is the harsh and rich
> harmonic content. The whole point of subtractive synthesis is to start with
> a lot of harmonics and then get creative about filtering those harmonics.
> p.s. I’ve never really seen a clear definition of what “soft sync” really
> means. Could your midpoint triangle sync fall into the soft category while
> peak triangle sync would fall into the hard category?
>

No, soft sync is when you only perform the sync reset under certain
circumstances, normally when the master oscillator has passed, say, 90 % of
its period. Then the synced waveform can have a lower frequency than the
master, and lock on to subharmonics (integer frequency divisions) of it.

/mr
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20180622/ebcfab11/attachment.htm>