[sdiy] Additive Synthesis questions

[Scott Nordlund]

>>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? 
> 
> Walsh functions?
 
That's how the RMI Harmonic Synthesizer does it, with some 
additional filtering.  It's quite crude, though, and will leave 
with a lot of higher harmonics (maybe not a bad thing if you've
only got 16 to work with).

>>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? 
 
Walsh functions would be the easiest, but don't assume will be 
simple, efficient, or really that exciting.  You could get similar
results clocking an analog sequencer with a high frequency VCO.  
The output of the RMI additive engine was a 32 step waveform, so 
you could get all the same results (and more, actually) by drawing
the waveform directly with the sequencer.  It's not as easy to work
with, but it's a great deal simpler, electronically. 		 	   		  
_________________________________________________________________
The New Busy is not the old busy. Search, chat and e-mail from your inbox.
http://www.windowslive.com/campaign/thenewbusy?ocid=PID28326::T:WLMTAGL:ON:WL:en-US:WM_HMP:042010_3