[sdiy] VCO - sine output - why bother?

[Mattias Rickardsson]

On 26 August 2016 at 12:04, Tom Wiltshire <tom at electricdruid.net> wrote:
> On 26 Aug 2016, at 10:38, Steve <sleepy_dog at gmx.de> wrote:
>
>> Then again, when I think in the box of "subtractive synthesis", in a strict
>> sense anyway, the suggestions of using a single sine wave to add a
>> fundamental after a VCF feels kinda odd :-D
>
> The only fixed-architecture synth I can think of that implements this trick
> is the Alesis Andromeda. There's probably one or two others, but it's
> certainly not a common feature.

You are unknowingly in desperate need of trying out some of Yamaha's
CS-80
CS-70M
CS-60
CS-50
CS-40M
CS-30
CS-30L

It might sound tiny, but it's not. The sine-bypassing-bandpassfilter
feature is one of their most powerful features, which makes these
synths really stand out as truly unique in their sound capabilities!

On 26 August 2016 at 17:48, Donald Tillman <don at till.com> wrote:
>> On Aug 26, 2016, at 1:52 AM, Oakley Sound <oakleylist at btinternet.com> wrote:
>>
>> You can add (or subtract) the sine waveform to your other chosen waveform to create more (or less) powerful sounds. Again sine seems to work better for this - or at least gives you more predictable results.
>
> This is great technique... except for a problem to beware of.
>
> Subtracting the sine waveform only works as intended when the phase of the sine wave is aligned with the fundamental component of the other chosen waveform.
>
> But the standard way of deriving a triangle and sine wave from a sawtooth core (ie., an absolute value circuit) leaves the phase of the triangle and sine 90 degrees from the sawtooth.  So one can't actually subtract out the fundamental in that situation.

That would be nifty, but I see the subtraction of the fundamental as a
minor feature after all. In fact, I'd say it's often useful to have
the sine wave unaligned with the fundamental by 90 degrees or so.
Because in a Yamaha CS-like filtering scenario, when filtering out the
fundamental (plus some more low harmonics) and adding a sine wave - if
the filter has an envelope or LFO (or is tweaked by the user) that
sometimes brings back the fundamental, then it will not collide and
add as strongly with the sine wave. They will work more together,
ensuring the fundamental is there, but not doubling the amplitude of
it when both sources are present.

> Other than my own designs, I don't know of any VCOs where the sawtooth and triangle/sine are correctly phase aligned.

I don't think I've seen one either. :-)

/mr