Circular pitch in Zebra

[Sendy]

Something I've been messing around with recently is circular pitch. We've all heard the Risset tone sweeps which seem to be constantly rising or falling, which are made from octaved sine waves and hence not very interesting.

However, it occurred to me, there are lots of ways to create something more interesting with Zebra (and presumably any other spectral synth worth it's salt). Effects such as 'odd for even' create a tone which morphs into a similar tone but perceptibly an octave higher or lower - without pitch sweeping. Sync does as well (though it sounds more 'pitchy'), as do many other processes such as rectifying a symmetrical wave such as a triangle or sawtooth.

So if you can set up an octave on the keyboard where the rise in pitch from A to A' is balanced out by an equal rise in the effect level of one of the aforementioned effects, you end up with a circular scale where A and A' sound the same, and notes between have highly ambiguous pitch height.

For my first try I created a wavetable which was a perfect triangle wave one end, and a rectified and normalized version of it the other end (geomorph). Using the modmapper I set up an octave on the keyboard such that A4 played the last wave of the table (which is rectified and hence sounds an octave higher) and A5 played the first wave (which of course sounds an octave lower).

Since the octave jumping in the wavetable is created by a spectral change rather than an actual frequency shift, this creates a really convincing circular octave based on a triangle wave, as walking up the scale key by key morphs from a high to low waveform, cancelling out linear pitch and making it circular.

It seems you can add effects which work on the amplitude level, to change the timbre without disrupting the illusion, but effects which work on the time level, such as symmetry, ruin it. I'll try using odd for even and sync next, and see how that works. Will post patches if anyone's interested!

p.s. My wavetable collection has grown considerably, I'll be updating it soon! I now have some sine-based morphs and some really interesting stuff with pulses and impulses.

[Bronto Scorpio]

This sounds like an interesting idea
Would be nice to hear some ausio examples!

I really like your wavetable collection and I'm looking forward to the update

Cheers
Dennis

[Sendy]

Ok, I posted a clip of this, as well as a few other 'Zebsperiments' I've been conducting recently. Let me know if the illusion works on your end

http://soundcloud.com/sendysynthdemos/zebsperiments3

[Bronto Scorpio]

Wow the illusion is really perfect!
Really nice idea and implementation!

Cheers
Dennis

[Sendy]

Thanks! There is a tiny spectral discrepancy at the point where the octave joins, but it's incredibly slight.