white noise shepard tones

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EATyourGUITAR
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white noise shepard tones

Post by EATyourGUITAR » Wed Nov 27, 2019 1:13 am

I have tested this and I can confirm that it works. instead of the traditional shepard tone that is done with some kind of phase locked additive synthesis. try using an array of bandpass filters on white noise. I did it in software but I think it would definitely work in hardware. the interesting bit is that you do not need the octaves to be tuned to octaves. if they are bandpass filters and white noise then you can tune them to any continuous function. it does not even need to be a base 2 log like 12TET. it could be linear or anti-log or any function. as long as you start them at equal spaced time intervals, the Hz scale will be a regular pattern regardless of center frequency slope shape.

you can also do this with one band if you have two bandpass filters. you could do it with low Q and more make up gain. you can do it with notch filters. I think there is something interesting that happens when you take plain wind noise or white ish noise and start making some subtle changes. then it kinda creeps up on you till you are deep in shepard tones. then you bring it back down again till the effect just fades out into thin air. there is a lot of stuff to try here!
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tuj
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Post by tuj » Thu Nov 28, 2019 10:46 am

makes sense, a bandpass filter fed noise is essentially a quasi-pitched oscillator. How many filters did you need in your quadrature or other LFO arrangement? Four? I've heard of the Shepard being doing with 6 oscillators/vcas as well.

cycad73

Post by cycad73 » Thu Nov 28, 2019 1:11 pm

Very cool, I might write a little plugin for this over the weekend. You do sort of get this endless motion if you use a frequency shifter in feedback with itself, at very low shift frequencies... but the explicit Shepard technique will give a lot more control over the results, and you can try also varying the parameters of the Gaussian envelope. Thanks for the inspiration!

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Post by jorg » Tue Dec 10, 2019 11:02 am

I've done that in Reaktor; a decently smooth effect required about 8 bandpass filters. I did an exponential sweep; spacing of the filters and their total range was adjustable. Basically the sweep LFO was a saw (8 saws) and the amplitude LFO was a raised sine (8 sines) locked to the saw. It was important to make sure the raised sine was at zero, at the moment of saw reset.

In stereo (16 filters/LFOs, offset by 1/16 of a cycle), the effect is like being in a spinning drum.

Here it is, starting at about 1:06 with a string-ish sound though the filter:
https://soundcloud.com/user-878664350/hemisphere

And with noise, at about 6:00 (fairly low in the background):
https://soundcloud.com/user-878664350/pentagon-city

colb
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Re: white noise shepard tones

Post by colb » Wed Jan 29, 2020 4:04 pm

You can get a sheppard tone / barber pole style phaser effect using a frequency shifter with a small shift, and some feedback.

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