[sdiy] MXR Pitch Transposer Schem/Circuit

[Steve Lenham]

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.


On 08/03/2013 16:13, Tom Wiltshire wrote:
> That's a damn interesting gizmo. Does anyone have any idea how it works?
>
> On 8 Mar 2013, at 15:32, Travis Thatcher <recompas at gmail.com> wrote:
>
>> While not technically SDIY (I apologize) I just got a black face MXR
>> Pitch transposer yesterday. Its a pretty amazing sounding piece of
>> gear with very little info on the web about it.  I did some quick
>> experimenting with the cv input and a sequencer and was very pleased
>> with the results but I was curious if anyone else had any experience
>> with these, particularly any mods or schematics.
>>
>> I'm assuming its an older bbd based design, though the chip which I'm
>> guess is the bbd has had the labeling info removed. It does great
>> pitch shifting and with the regen cranked it goes from weird flanger
>> to space sounds pretty quickly. It sounds very similar to a friend's
>> mxr flanger that I fixed so I'm assuming the circuit is roughly the
>> same. Kind of interested how it works!
>>
>>
>>
>> --
>> http://www.travisthatcher.com
>> http://www.soundcloud.com/travisthatcher
>> http://voiceofsaturn.blogspot.com
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