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

[rsdio at audiobanshee.com]

On Jun 22, 2018, at 4:34 PM, Tom Wiltshire <tom at electricdruid.net> wrote:
> On 22 Jun 2018, at 23:24, Mattias Rickardsson <mr at analogue.org> wrote:
>> The sync-behaviour in the CEM3340 
>> simply switches the load/unload "direction" of the VCO-core. So it does 
>> not(!) do a reset, like the hard sync does in a saw core VCO.
> 
> …and that’s why hardly anyone ever used the default datasheet “sync” circuit. Instead, pretty much all the commercial synth manufacturers went for the circuit that mimics the typical ramp-core VCO reset sync, "Figure 5" which appears on page 6 of the datasheet. Curtis clearly thought that their version was more interesting and did something new, but actually most people wanted the sync sound they already knew and loved.

Considering the original goal - to reduce the discontinuity at the point of sync - reversing the direction of the triangle is the ultimate solution. It has no first order discontinuity (although it does have a second order discontinuity). It’s a lot better than merely cutting the discontinuity in half.

The fact that nobody (?) used the Curtis CEM3340 feature commercially may give us our answer as to whether the goal is a useful one. However, perhaps no engineer allowed the reversing triangle sync out into the field long enough for musicians to hear what it offered and make use of it where appropriate.

I’d certainly like to hear what hard sync sounds like with a triangle core VCO that reverses direction in response to sync pulses.

Brian Willoughby