[sdiy] Pitch shift in modulated BBD delays

[Paul Perry]

Whatever the common "chorus" effect produces, it certainly isn't anything
remotely like an actual chorus.
I suspect that replacing the regular LFO with a 1/F (fractal) noise at low
frequency would be much more plausible.

paul perry Melbourne Australia

On Wed, Jun 17, 2026 at 7:49 AM Tom Wiltshire <tom at electricdruid.net> wrote:

>
>
> On 16 Jun 2026, at 21:21, Gordonjcp <gordonjcp at gjcp.net> wrote:
>
> On Tue, Jun 16, 2026 at 02:20:42PM +0100, Tom Wiltshire wrote:
>
> I've spent a long time wondering about how the LFO waveshape relates to
> the final pitch shift you get when modulating a BBD clock, as you would in
> a Chorus or Flanger circuit. Or even a delay-based analogue vibrato, come
> to that.
>
> I recently managed to get some interactive demonstrations done, which I
> think make the whole thing a lot easier to understand. Here's the finished
> article. Perhaps some of you will find it interesting.
>
> https://electricdruid.net/weird-wiggles-bbd-clock-modulation/ <
> https://electricdruid.net/weird-wiggles-bbd-clock-modulation/>
>
> Any thoughts, comments, or error-spotting appreciated.
>
> Thanks,
> Tom
>
>
> So where does that actually happen? The chorus in the Juno 106 at least is
> modulated with a triangle wave at the same amplitude and one of two speeds,
> and gives a very distinct pitch shift - but that shift is dead steady,
> sharp/flat/sharp/flat deedaahdeedaah like a toy police car.
>
>
> I'm not entirely sure what you're asking. "Where does that
> happen?"...Where does *what* happen?! It happens in the circuit, right?!
>
> If I'm interpreting you correctly,  I think that if you play with the sim,
> setting the LFO waveform to triangle, and the delay stages to something
> short (is it 256 or 512 in the Juno? I don't remember without looking it
> up) and most importantly set the modulation type to "Linear Period", you'll
> see a "deedahdeedah" pitch shift. It seems a lot like realising modulation
> of the clock *period* rather than the *frequency* was what gave Roland
> the edge in the chorus world. Given that, increasing the clock
> frequency/shortening the delay reduces the pitch shift. Lowering the clock
> frequency/lengthening the delay increases the pitch shift. Changing the LFO
> Frequency or Depth also has an effect. The sim shows the differences.
>
> https://electricdruid.net/modulated-bbd-delay-simulation/
>
> T.
> ________________________________________________________
> This is the Synth-diy mailing list
> Submit email to: Synth-diy at synth-diy.org
> View archive at: https://synth-diy.org/pipermail/synth-diy/
> Check your settings at: https://synth-diy.org/mailman/listinfo/synth-diy
> Selling or trading? Use marketplace at synth-diy.org
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20260617/5d996e23/attachment.htm>