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From: Doughy on 25 Jul 2007 18:42
Hello all,

I am a signal processing engineer and also a guitarist. I would like
to start messing around with creating my own effects, and was
wondering the best DSP to do so.

Let's say that I want to build a DSP stompbox, with one 1/4" input,
and one 1/4" out. I want to hook the DSP up to some knobs for
parameter control, and maybe have a simple screen which can display
levels, etc..

Which DSP would suit itself best for this application? Would I need a
microcontroller as well to load the DSP and control the knobs and
screen? Any suggestions for a beginner? In the end, I would like to
have an actual stomp box that I can use in real world gigs.

Thanks.

-Joey

From: Eric Brombaugh on 25 Jul 2007 20:43
Doughy wrote:
> Hello all,
>
> I am a signal processing engineer and also a guitarist. I would like
> to start messing around with creating my own effects, and was
> wondering the best DSP to do so.

Depends on what you want to do and how much you want to spend. For
low-end stuff, Microchip dsPIC processors are cheap, easy to interface
and easy to program. They're not super fast though, so they won't be
good for complex processing. For more complex processing you'd probably
like to try ADI & TI DSPs that run much faster.

Eric
From: Jonny Barker on 28 Jul 2007 18:08
Hi,

Funny you should mention it - I've just been building a dsPIC based guitar
effects unit. It consists of a dsPIC33FJ64GP706 (which i got free off
microchip), and a CS4270 and lots of capacitors (which i didn't get free
().

The main limit I've met so far is RAM, which limits the amount of
reverb/delay you can add. My chip has 16kb, enough for a fairly muddy
bathroom-sounding reverb, but little more.

With ~500 cycles per sample (48khz stereo) and a one-cycle MAC it is
possible to do a fair bit of FIR/IIRing, I haven't really stretched it yet
though (haven't figured out what I want it to do!).

Jonny

Eric Brombaugh wrote:

> Doughy wrote:
>> Hello all,
>>
>> I am a signal processing engineer and also a guitarist. I would like
>> to start messing around with creating my own effects, and was
>> wondering the best DSP to do so.
>
> Depends on what you want to do and how much you want to spend. For
> low-end stuff, Microchip dsPIC processors are cheap, easy to interface
> and easy to program. They're not super fast though, so they won't be
> good for complex processing. For more complex processing you'd probably
> like to try ADI & TI DSPs that run much faster.
>
> Eric

From: Eric Brombaugh on 30 Jul 2007 12:52
Check this out:

http://www.modcan.com/bseries/ddelay.html

I did the firmware.

It uses a similar configuration to what you've got, except with a higher
pincount processor so we could address a fairly large external SRAM
through GPIO for the delay memory.

I've got a 2nd order IIR in there to add some color when desired. It
doesn't use too many cycles. I'm actually running to processor at a
lower clock rate because I don't need the speed in this application.

Eric

Jonny Barker wrote:
> Hi,
>
> Funny you should mention it - I've just been building a dsPIC based guitar
> effects unit. It consists of a dsPIC33FJ64GP706 (which i got free off
> microchip), and a CS4270 and lots of capacitors (which i didn't get free
> ().
>
> The main limit I've met so far is RAM, which limits the amount of
> reverb/delay you can add. My chip has 16kb, enough for a fairly muddy
> bathroom-sounding reverb, but little more.
>
> With ~500 cycles per sample (48khz stereo) and a one-cycle MAC it is
> possible to do a fair bit of FIR/IIRing, I haven't really stretched it yet
> though (haven't figured out what I want it to do!).
>
> Jonny
>
> Eric Brombaugh wrote:
>
>> Doughy wrote:
>>> Hello all,
>>>
>>> I am a signal processing engineer and also a guitarist. I would like
>>> to start messing around with creating my own effects, and was
>>> wondering the best DSP to do so.
>> Depends on what you want to do and how much you want to spend. For
>> low-end stuff, Microchip dsPIC processors are cheap, easy to interface
>> and easy to program. They're not super fast though, so they won't be
>> good for complex processing. For more complex processing you'd probably
>> like to try ADI & TI DSPs that run much faster.
>>
>> Eric
>
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