[sdiy] MXR Pitch Transposer Schem/Circuit

Tom Wiltshire tom at electricdruid.net
Sat Mar 9 16:34:50 CET 2013


Thanks, Steve. The Spin Semi pages are a goldmine. For anyone who hasn't visited, I recommend:

http://www.spinsemi.com/knowledge_base/effects.html

T.

On 8 Mar 2013, at 16:44, Steve Lenham <steve at bendentech.co.uk> wrote:

> Unless the blackface version is very different to the blue one I worked on, the MXR pitch transposer isn't a BBD design. It is a digital one, with an 8-bit logarithmic ADC/DAC and a small block of RAM.
> 
> Basically a circular buffer is set up in the RAM, with a read and a write pointer which chase each other round at different rates. Some fancy crossfading is done to get rid of the discontinuities when the pointers cross over.
> 
> For a better insight, go to www.spinsemi.com and search around for information on the pitch shifter algorithms for their FV-1 effects DSP. Spin Semi was set up by the late Keith Barr, who IIRC founded both MXR and Alesis, and the software algorithm seems to follow the same principle as the MXR hardware.
> 
> Almost as cool as the effect itself are the touch-sensitive knobs - when you touch any of the four preset shift-amount knobs, it automatically selects that preset, so you can hop instantly between different effects.
> 
> HTH,
> 
> Steve L.



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