[sdiy] Additive Synthesis questions

[Richard Wentk]

On 8 Apr 2010, at 17:10, Paul Cunningham wrote:

> Ian -- There's nothing different between the output stage of a digital additive synthesizer and one that uses sampled waveforms or wavetables or whatnot. They all use a D/A converters.

They do, but there is a difference between the possible bit depths, cycle lengths and interpolation options.

> 
> I also gotta warn you that additive is really not that rewarding unless you have an awesome filter, or have some way to dynamically control the relative pitch and amplitude of individual harmonics. This is what the Synergy and Kurzweil 150 did and the results are sonically remarkable when compared to static waveforms! The K150 has up to 64 partials controlled by one of 8 different envelopes as well as other modulators (i think).

Additive really needs to be smart to be interesting. Mashing together the partials is the easy part. Giving the partials something interesting to do over the duration of a note is the only way to make additive stand out from other synthesis options. 

Ideally you really want to be able to do resynthesis - pulling sounds apart automatically, and reconstituting them with additive+effects. (Random or organised frequency+time+amplitude modulation, stretching/squashing the overtones, and so on.)

24 partials is a bare minimum, 32 is better, 64 is better still, but not so much better that it's worth going insane over an implementation if resources are scarce. 

Richard

> 
> You can start with 9 sine waves. That's what the Hammond's got. If you do it in analog, that would be sweet! Hopefully that will be easier than what must have happened inside a Vox Continental. ;-) -pc
> 
> On Apr 8, 2010, at 11:42 AM, Ian Smith wrote:
> 
>> 
>> Hey all,
>> 
>> This is more of a hypothetical sort of thing at the moment since I'm working on a couple big projects at the moment. Anyway, I was reading Cheater's thing on stretched harmonics, and I was wondering about additive synthesis.
>> 
>> I think my biggest question is: Is there a noticable difference between adding up a bunch of sine waves and sculpting a waveform with a, my mind fails me on the name, but a quickly sequenced series of voltages fed through a D/A converter or R/2R ladder?
>> 
>> If I was going to make an analogue additive synthesizer, is there a simple way of building a sine wave oscillator with just a few parts that aren't some expensive special function chips?
>> 
>> What would be a good number of sine waves for analogue additive synthesis? 4, 7, as many as can be crammed on a panel?
>> 
>> thanks all,
>> 
>> Ian (always bloody curious) Smith
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