[sdiy] Frequency shifted from BBD?

[Mattias Rickardsson]

Don't you mean that you need a trapezoid wave for the crossfade? Keeping
one delay quiet for a while while emptying its period of accumulated
control glitch... which I expect to be slightly longer than an instant...
No? :-)

/mr

Den fre 4 okt. 2024 22:41brianw <brianw at audiobanshee.com> skrev:

> On Oct 4, 2024, at 12:26 PM, Ingo Debus wrote:
> > Am 04.10.2024 um 19:49 schrieb Gordon:
> >>> I recently re-read the section in Barry Klein’s Electronic Music
> Circuits on bucket brigade devices and noticed a brief mention of using
> them as a frequency shifter by modulating with a ramp wave.
> >>> He acknowledges that there will always be an audible glitch and some
> noise issues.
> >>> I experimented with this idea a little to minimal success, but curious
> if anyone else has tried this or seen it used in interesting ways.
> >>>
> >>
> >> Didn't the Eventide harmoniser basically do this by ramping two delays,
> and crossfading from one to the other when one was about to "jump" and the
> other was mid-sweep?
> >
> > Surely this would result in a pitch shift, not a frequency shift.
> >
> > Ingo
>
> Yes, this would be a pitch shift.
>
> The BBD uses a single clock for input and output. There is no way to clock
> voltages in at a different rate than they're clocked out, nor can the
> sample "address" be random access.
>
> The pitch shift works because the clock is constantly increasing (or
> decreasing) so that the output rate is effectively different from the input
> rate that was active when that particular sample was taken. But the caveat
> is that new samples are already coming in at the new rate.
>
> As Gordon mentioned, having two parallel setups and crossfading between
> them helps. You'll need a triangle wave (for the crossfade) and two ramps
> offset from each other. At the top of the triangle, one ramp will be in the
> middle (no glitch), while the ramp that's completely faded out is recycling
> (glitch, but fully attenuated). Then, at the bottom of the triangle, the
> reverse is true. I can't remember seeing the oscillator design that would
> create these three synchronized signals. The two ramps would have to be at
> exactly the same slope, but their reset point would be offset so that they
> alternate in sync with the triangle.
>
> Brian
>
>
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