[sdiy] analog pitch shifter circuit?

[Theo]

If you could live with a latency of one 48khz sample, you might want to take
a look at the wavefront (was Alesis) 3201"reverb".
Wavefront also have AD and DA to match.
All low pincount, no high external frequencies, this stuff is happy on a
(smd type) proto board.

There is a example code demo-ing pitch shifting in the application notes
(off-center 45rpm effect), not 100% what you need but close enough to adapt.
Cause this is not a standard program of the 3201 a additional uC is needed
to load the code and set your transpose values.
A small PIC or AVR will do, you need only to steal 520 bytes of its memory
for the 3201 program.
After loading the 3201 the uC would have nothing more to do and sit idle.
But with a uC onboard you can always add midi or extra knobs and buttons for
live action at a later time :)

The 3201 is bad at filtering, it might be a good idea to LP filter the input
at 10...12khz,
this leaves you enough frequency space to pitch shift one octave up without
aliasing problems.
You might be satisfied without this input filtering though.

For guitar stompbox quality this is all hardware you need.


Theo
Working on a multi purpose box starring AVRmega8, 3101DSP and 3201SCR in the
lead roles.
Programs for it so far are 'Distressor' and 'Distorture' FX, next up a
filter something and VA drum sound thingy.




----- Original Message -----
From: <synthplayer88 at spymac.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, January 04, 2005 11:28 AM
Subject: Re: [sdiy] analog pitch shifter circuit?


> The problem is the sampling frequency at ONLY 8 khz which will only
capture less
> than 4Khz, that is pretty pathetic..... To increase the performance you
would
> need increase the memory running and running at a higher sampling rate,
not to
> mention the processing power of the chip.....
>
> Might as well build the whole thing from scratch and choose your own AD
> converter, uController with built in ROM and external ram then convert D
to A.
> After you figure out how to write the assembly code to achieve this......
>
> What I am afraid of is latency, which is critical dependent on your
assembly code...
>
> Any more thoughts guys?
>
> I think I am going to give up doing this in analog but until I am close to
any
> good at programming in DSP, I am gonna have to give up doing this.....
>
>
>
> On Tue Jan  4  2:19 , Andreas Gaunitz <andreas.gaunitz at konstfack.se> sent:
>
> >I noticed in the specs that it can go up 1 octave, but only a third of
> >an oct down. I wonder what would happen if you used 2 in a row, or used
> >feedback...
> >
> >-Andreas
> >
> >-------------------------------------------------
> >
> >2005 jan 04  kl. 00.03 skrev rdrake:
> >
> >> as you say, probably very lo fi:
> >>
> >> http://www.j-tron.com/pom.htm
> >>
> >> but for $15, i'll probably give it a try.  hey, it's 2005: lo-fi is
> >> the new black...
> >>
> >> lbd
> >>
> >>> From: synthplayer88 at spymac.com>
> >>> To: synth-diy at dropmix.xs4all.nl>
> >>> Sent: Monday, January 03, 2005 4:35 PM
> >>> Subject: [sdiy] analog pitch shifter circuit?
> >>>
> >>>
> >>> Hi guys,
> >>> I was wondering if anyone know how does the boss
> >>> voice transformer achieve
> >>> the
> >>> voice pitch shifting?
> >>> I would like to build an analog pitch shifter
> >>> does what the Boss voice
> >>> transformer do but I am not sure if that is an
> >>> analog circuit, since all
> >>> their
> >>> new pedals such as the  PS3 and PS5 are all
> >>> digital circuits.
> >>>
> >>> I came accross this chip that does pitch shifting
> >>> but only has preset
> >>> shift and 8
> >>> Khz sampling rate :(
> >>> which seems to be kinda lo fi...
> >>>
> >>>
> >>> http://www.holtek.com/english/docum/consumer/8950.h
> >>> tm
> >>>
> >>> Does anyone know of any monolithic IC that can do
> >>> what this IC does but
> >>> with more
> >>> flexibility? eg. allows precise pitch shift of
> >>> any notes up to serveral
> >>> octaves.
> >>>
> >>> Oh, please do not suggest any DSP or
> >>> uControllers. I would like to avoid
> >>> ANY
> >>> programming and looking for a simplest circuit to
> >>> do this if possible :)
> >>>
> >>> How can I apply FM into this? eg. multiply the
> >>> sound source by 2, 4, 8
> >>> hz.....
> >>> Can this be done?
> >>>
> >>> Thoughts?
> >>>
> >>>
> >>
> >
>
>