[sdiy] Divide down question

[Scott Nordlund]

> Like the Korg PS series. One oscillator for each note, sawtooth master
> with divided down squares summed to create the saw suboctaves.

I think the Polymoog did the same.  It's nicer than a pseudo-saw built from summed square waves.

> Dave
>
> Scott Nordlund wrote:
>> It could be done with sawtooth waves too: use a comparator to make a square wave, invert it, amplify the sawtooth by a factor of two, and mix the two. Of course the comparator's threshold has to be adjusted properly, or there will be asymmetric pulses and sub-harmonics sneaking in...
>>
>> Pulse waves would be more difficult. The thing with sawtooth and triangle waves is that you get an instantaneous one-to-one mapping of input amplitude to however many octave-doubled outputs you want. You obviously can't do this with square or pulse waves, since the amplitude isn't continuous. You could use a phase locked loop with a frequency divider in the feedback loop (so the frequency can be multiplied by any arbitrary number), but this needs time to adjust to changes in frequency. It won't be instantaneous like the sawtooth or triangle-derived, and it can have objectionable glitches and artifacts. But you could potentially get all the octaves you want in one go, deriving them from the frequency divider in the feedback loop.
>>
>> ----------------------------------------
>>> Date: Mon, 24 Aug 2009 19:37:36 +0100
>>> Subject: Re: [sdiy] Divide down question
>>> From: cheater00 at gmail.com
>>> To: synth-diy at dropmix.xs4all.nl
>>>
>>> Tom,
>>> extremely interesting! I should think about that for a while. This
>>> 'multiply up' as I would call it is especially cool. Any sound
>>> examples?
>>>
>>> Which makes me wonder: can you do that with pulse waves..?
>>>
>>> I think you could almost certainly do that with sawtooth waves.
>>>
>>> D.

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