Super short delay with 3207

[rowanelgee]

Hi guys new to the forum so let me know if im posting in the wrong place.

Im trying to build a detune like effect, similar to if you would layer two square waves together and detune one by +/- 2 cents. I have a few mn3207 chips, just trying to figure out the simplest way of doing this.

Presumably splitting the signal, then delaying one by the shortest amount the 3207 will allow then mixing them back together, using a pot or possibly lfo to change delay time? Im slightly unsure about whether the 3207 needs a clock to allow it to delay signals, or whether that is just for chorus effects?

anyone know of any schematics of this already around??

Thanks a lot
R

[Mark Hammer]

Detuning with a BBD is achieved by changing the clocking of the chip such that sampling out is at a different rate than sampling in.  Basically, you are describing a chorus pedal.  The extent of detuning would depend on how much an LFO changes the clock/sampling rate, and what the basic sampling rate is.  .

[anotherjim]

If it's a constant detune you need, it's complicated & I'm not sure if it's actually been done with BBD's (plural -  it will need at least 2). Otherwise, get a 12string guitar

Anyway, you need to clock a short "frame" of audio into a BBD (exactly as long at it takes to fill all the BBD stages). The moment the 1st BBD is full you stop its clock & start filling another one. While that's filling you can play the first frame out at a slower clock from the first BBD for as much time as it takes to fill the second.
It won't be smooth because the duration of audio stored doesn't match with real time, so you need to crossfade the playbacks to hide any glitches.
I think this is kind of close in a way to the original intended use of BBD - time compressing speech before multiplexing many calls down a single carrier.

[robthequiet]

http://www.experimentalistsanonymous.com/diy/Schematics/Chorus/Zombie%20Chorus%20MN3207%20Based.jpg

CD 4046 possibly obtainable from Small Bear

PS Might find a layout in the gallery...

[Mark Hammer]

One way to get a constant detune is with a frequency shifter, but trust me that is very complicated.  Perhaps even more important is that frequency shifters add a constant to the entire signal, such that every little bit of, including harmonic content, is nudged over by some fixed amount (e.g., add 23hz to absolutely everything about the signal).  It bears some modest relationship to a ring modulator in terms of how it sounds to us, but isn't the same thing.

[rowanelgee]

yeah my plan was to use two bbd's anyway, the amount of delay/detune needs to range from 1ms to 10ms, so thats way lower than one can allow anyway. As this would be splitting the signal and applying a BBD to both signal paths, would it badly affect the frequency range? I would like a flat frequency response if possible, the low end in particular of the affected source sound is really important

Looked at frequency shifting, but thats a whole new rabbit hole to go down. The effect is basically a really short chorus yeah, just needed some clarification.

The project is for a distortion/fx/filterbank project, mostly used for affecting synth sounds, was looking at the zombie chorus, going to order the cd4046 today I think.

Have any of you guys experimented with interactive ways of modulating certain parameters? i.e. ldr's or accelerometers in place of pots?

Thanks for the responses!

[ElectricDruid]

During my own experiments with 3207-based flanging, I found you can clock the 3207 at up to 500KHz or so before you start to see significant signal loss. That gets you down to 1msec. You can go higher, but the delay signal starts to wane, and you start to need a lot of buffering to drive the clock pins hard enough to overcome the capacitance (there are other threads on this topic here if you're interested). But you could certainly build a chorus with a very short delay if you wanted to.

HTH,
Tom