odd pedal request - MICROSHIFTING

[Rixen]

I think BBD's could be used to implement an analogue version of a pitch shifter, if one were to generate the clocks with a micro and control the crossfading between the delay lines.. must have been done before ?

[Transmogrifox]

I think BBD's could be used to implement an analogue version of a pitch shifter, if one were to generate the clocks with a micro and control the crossfading between the delay lines.. must have been done before ?

I was thinking the same thing.  This is essentially what I consider to be the barberpole effect.  You don't really need a micro to generate the clocks though -- you can make a polyphase LFO without involving software.

You can make 4 choruses all ramp-modulated at 90 degrees of each other and use a triangle (derived from the ramps) to drive a VCA.  All 4 add at the output.  One is always fading in while another is fading out.

Either way if LFO is set up to change BBD frequency (or PT2399 freq) by modulating the PERIOD directly then you get a constant pitch shift from each output. 

Traditionally the effect is used to create the illusion of a constantly rising flanger that never resolves and never seems to start over but it stands to reason that it might work ok if sent off to a different channel.

Really this is done best in the DSP world as mentioned above, but if you're not a programmer or digital hacker then you're SOL on that front.

If the warble of an LFO was acceptable then a stereo chorus really seems like the simplest hardware solution.  A chorus modulated with a more randomized CV input could help.  Multi-chorus better...then you're talking about the barberpole idea.

Just some brain vomit to consider.

[ElectricDruid]

Two analog solutions have been proposed:

1) Analog BBD-based pitch shifter (barber's pole effect)
This is possible, but needs a multiphase LFO and multiple BBDs - at least three, plus VCAs to go with them. That's quite a lot of circuit.

2) Analog frequency shifter
Also possible, but also quite involved. As RG said, you need phase-shifting filters, plus the quadrature LFO, and a pair of multipliers.

That's just to do the "shift" part. The other bits are easy. Split the signal, run one side through short delay (and I'd say "flanger range" rather than "chorus range" - a handful of msecs, tops) and output to stereo.

Adding a warbley pitchshift to that by adding an LFO to the delay clock is simple. Getting a static shift of even a few hertz is difficult - that's what the complex solutions above do.

Personally, I'd try the easy bits and see if that's enough. If not, then maybe consider the tough stuff. But you might be lucky and discover that a simple delay, or a simple modulated delay is enough to get the effect you need.

Tom

[duck_arse]

well kle333, looks like you've got a few methods to think about.

I've got to say I really liked the accordian whistling. the others were .... a bit .... haunting? affecting? but interesting.

[edit for spelling]

[Strategy]

It's an ambitious project, but there are several Boss Dimension C projects out there -- Toppopiccione and some PCBs for a rack mount style unit from the late synth DIY guru Juergen Haible. Its what I immediately thought of when I saw your first post

[Transmogrifox]

...Juergen Haible...

That name is the very next thing that pops into my mind when the term "dome filter" is mentioned.  I remember looking at one of his dome filter circuits.  As pointed out above it's a pretty ambitious project.
RIP JH

[armdnrdy]

Maybe something like this can be tailored to meet the OPs needs?

Not really a stompbox sized circuit.

http://www.all-electric.com/schematic/bbdbox.htm