[music-dsp] Fw: A little question about DSP performance

douglas repetto douglas at music.columbia.edu
Sat Oct 3 10:12:19 EDT 2009


It's here:

http://music.columbia.edu/cmc/music-dsp/sourcecode/gwenhwyfaer_sawphase.zip

Gwenhwyfaer wrote:
> On 03/10/2009, robert bristow-johnson <rbj at audioimagination.com> wrote:
>> On Oct 3, 2009, at 1:53 AM, Didier Dambrin wrote:
>>> And then you start your sines at random (any random generator) phases
>>> instead of zero, there's really nothing special.
>> okay, i have done that experiment too, the file that i posted does
>> *something* like that (not random, but i let some of the phase slide
>> ahead, others slide behind, and they line up opposite polarity in 1/2
>> 1/change_rate, the square gets spikey).
> 
> So have I, and here are my results, together with the generator
> program I wrote (I used wavosaur to glue the raw files together into
> wave files; it seemed quicker than looking up the WAV header format)
> and a list of the harmonic phases. The file's at
> 
>     http://www.isle-of-avalon.co.uk/sawphase.zip
> 
> for the next week - but it's a 1.4MB file, and I only get 100MB of
> bandwidth a month, so please be gentle :) and if someone wants to
> mirror it, that would be wonderful! I apologise in advance for the
> roughness of my C. Corrections are welcome.
> 
> Results? Firstly, I think normalising each individual sawtooth was a
> mistake. Secondly, I can hear a difference between the straight
> sawtooth and the ones with randomised phases, but again, only via
> headphones (same rig as before) - they all sound identical over
> speakers. Thirdly, the difference is *far* less audible to me than the
> difference between Didier's waveforms, which makes me wonder whether
> the differences are not the result of varying the phase at all...
> 
> Anyway, that's my contribution to the debate. It's nice to read
> something here that doesn't go completely over my head. :-)
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