[sdiy] Screwing with Square Waves

cheater00 . cheater00 at gmail.com
Mon Nov 4 08:04:13 CET 2013

On Mon, Nov 4, 2013 at 12:10 AM, Tom Wiltshire <tom at electricdruid.net> wrote:
> On 3 Nov 2013, at 22:14, Mattias Rickardsson <mr at analogue.org> wrote:
>> On 3 November 2013 11:12, cheater00 . <cheater00 at gmail.com> wrote:
>>> On 3 Nov 2013 00:21, "Mattias Rickardsson" <mr at analogue.org> wrote:
>>>> detuning two of them wouldn't give the flanging effect that we're used to,
>>>> since the overtones aren't faded in/out in a specific order.
>>> Why wouldn't they be? Flanging is perfectly well explained in the time
>>> domain. It has a specific transfer function given by the amount of delay and
>>> the feedback, and nothing more. The transfer function does not depend AT ALL
>>> on the program pushed through it. A perfect flanger sounds the same on two
>>> waveforms that sound the same. An analog flanger might sound very different.
>> I'm sorry - I wrote flanging, but was referring to adding two
>> *differently* random-phased signals. Two signals with square-wave
>> spectra, but with random phases on all the partials. And then flanging
>> (in the most original meaning of the word) them against each other.
>> That should sound quite different, right?
>> It was after midnight and I should have gone to bed instead... :-)
>>>> Often it feels like we use synth waveforms near the limit where our
>>>> hearing starts to sense the separate edges of the waveforms. In bass
>>>> frequencies very much so. And I get the feeling that it can give a
>>>> kind of listening fatigue, especially when hearing very dry synth
>>>> sounds. Maybe the random-phase variants are the solution?
>>> I think this is a great idea.
>> Does any synth use it?
> There may be others, but I used it on my PIC VCDO, which appears in the Frequency Central Waverider module:
> http://www.electricdruid.net/index.php?page=projects.vcdo
> http://www.frequencycentral.co.uk/?page_id=845
> <End of shameless plug>
> This is basically a wavetable oscillator.
> If you crossfade between waveforms where all the harmonics have the same phase, you get a linear result - a smooth crossfade. The typical wavetable oscillator has all the harmonic phases starting from zero, since it makes everything nice and predictable.
> But that's a bit boring, or at least not as interesting as it could be. So before putting the waveforms into the data tables, I made sure to randomise their phases. This means that when you move through the wavetable, you get nonlinear results, where the amounts of each harmonic are *not* simply linearly interpolated from one waveform to the other. It's pretty subtle, but it's there. There are combinations between one and another waveform which are not a simple blend of the two endpoints - they might have all the third harmonic of the second waveform, but all the fourth of the first waveform, and a combination of the 7th of both, for example. Hiding stuff like that in my code is what I live for! One day I'll get a life, but for now, code will do.
> Tom

Sounds like fun. I'm interested in sound comparisons of a square wave
vs a randomized-phase square wave analog at 20 Hz and the same two
waves at 1 kHz. The additive expansion should contain at least 1000
harmonics for the 20 Hz example.


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