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Re: DSP Device for Guitar Pedal Effect



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You must have some pretty trivial problems then.

Re: DSP Device for Guitar Pedal Effect



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One design was a legacy (1996) counter driven state machine pwm driver
with less than a dozen ttl devices and an eprom. A gate array looked
attractive and would have been a good excuse to get into a bit of vhdl,
but it was a lower cost solution to use a silabs 8051 micro as a one
chip solution and already had the tools from other projects. The other
thing was design tools. Yes, you can download demo versions, but you end
up with Gbytes of hard disk space. Even using the smallest gate array
from Lattice would have been uneconomic compared to the micro solution,
and would still have needed the eprom.

So what complex problems are you solving with gate arrays and what
speeds ?...

Regards,

Chris

Re: DSP Device for Guitar Pedal Effect



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IOW, pretty trivial stuff.  I'd likely use an 8051 for that too (and
pass the crap job off to the firmware group ;-).

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So what?  A 1TB drive is under $100.  BTW, they aren't "demo
versions".  They're fully capable versions, just somewhat limited
(usually something like <1M gates and <10KLOC testbenches).  I have
Xilinx, Altera, and Actel software on my systems.  Our disty said he
was bringing the Lattice stuff by next week in case the Altera CPLD
didn't work out (he gets paid for either).  It's good to keep 'em
guessing.  ;-)  

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Nonsense.  I have two solutions (one Actel FPGA and the other an
Altera CPLD) for another pretty trivial problem, both under $2.50, no
EPROM/flash required.
 
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My current "problem" is also pretty trivial[*], yet an FPGA (or CPLD,
not sure which) still makes a lot more sense than yet another micro
and piles more software complexity.

[*] Though it saves something like one-third of the $150 BOM times
$5K-$10K, per year.  The FPGA/CPLD is only a part of the savings,
though.

Re: DSP Device for Guitar Pedal Effect



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In my small company, I *am* the firmware group, and think software
design far more than hardware these days :-).

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Not so cheap in the uk in small quantities and more expensive than an
silabs 8051. Using a gate array, would still have needed the eprom, as
the sine tables wouldn't fit, whereas they just go in code space using
an mcu. I get other benefits like self test, an a-d for soft start,
voltage regulation, current limiting etc and a serial port for status
messaging. There's even a temp sensor on chip !. Makes a far more
capable product for a couple of weeks of software effort, which you
would need anyway using vhdl.

As an aside and have no commercial interest, the Silicon Labs fast 8051
series are quite amazing. They are typically 50 mips risc cored updates
of the 8051 architecture and the dev kits range from ~$100 down, with
all the hardware and dev tools. You can get started building and running
the simple demos out of the box within 30 minutes or so. I don't really
rate the 8051 architecture that highly, but the latest versions do a
good job even with everything written in C.

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I guess everything's software now, even hardware design, so if there's
not much difference in cost, it probably comes down to what you are most
familiar with in the end...

Regards,

Chris

Re: DSP Device for Guitar Pedal Effect


I see the Spin chip is 6 MIPS, at 48kHz sample rate that only allows
about 125 instruction steps per sample.  I was thinking of some thin
with at least 30 MIPS.

I see those Silicon Labs devices run at 50 and 100 MIPS, that would
allow a higher sampling rate.  Other thatn that they seem overly
capable.

I only need 1 ADC input and 1 DAC output, and whatever I/O necessary
to support table data if used.

Regards,

Fred



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Re: DSP Device for Guitar Pedal Effect


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The si labs stuff is very good for a certain class of project and they
are fast, but couldn't say for sure that they would have enough real
time capability for audio sampling and processing. They are an 8 bit
architecture and any code that requires 16 or 32 bit operations will
result in a lot of code. The kits are very low cost though and modelling
the application, possibly at a lower data rate and resolution, would
provide a lot of insight in terms of what was really needed for the
task, especially if you have no previous experience of dsp solutions (I
don't, either :-).

Some of the variants have 24 bit adc's which would be more than good
anough if the sampling rate is high enough. You could use a timer driven
interrupt level state machine to control the adc and to connect the
samples to the mainline code processing section. It may very well be
possible, but you may need to add an spi 16 bit dac to get the final
analog output...

Regards,

Chris

Re: DSP Device for Guitar Pedal Effect


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Analog and Infineon 16bit devices are looking good, their in the 40-80
MIPS range.  There's a few PIC that might work too, 32MIPS though.

I guess it will take me a while to sort thouugh all the
canidates... :)

***

BTW I  just realized that I could easily sim the algorhythm with
behavioral sources in SPICE, so I've been making audio clips and
running PCM files though that.

It's good to see and hear the idea in action, especially since I've
had it on hold for years now.

Regards,

Fred

Re: DSP Device for Guitar Pedal Effect


On Fri, 6 Nov 2009 13:36:41 -0800 (PST), Fred

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I don't know how versatile you are, but you could try capturing
several input waveforms, and running them through the algorithms on
your PC and playing them back.

Re: DSP Device for Guitar Pedal Effect


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Been doing that.  I have a digital multi-track that that I record a
guitar part on, then transfer to computer, through a digital to analog
back to digital process.  It's an old unit, although the results are
tolerable.

After I have the wave file on the computer, I use that as input for a
voltage source in SPICE and output the processed voltage to another
wave file that I can play with a media player to hear.

It's really a trivial process.  I could have done this years ago had I
realized SPICE's PCM abilities.  :)

Re: DSP Device for Guitar Pedal Effect


On Mon, 9 Nov 2009 09:27:08 -0800 (PST), Fred

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Yes.  Kazaam.  PWL (piece wise linear) sources in SPICE can illuminate
many ideas nicely.  Also PWL file IO.

Re: DSP Device for Guitar Pedal Effect


Hi Fred,

I designed and built a DSP board using the Wavefront AL3102 (48 MIPS), the
WM8731 CODEC (24 bits/sample, 48 kHz) and an Atmel microcontroller (DSP
program
loading/storage and control) that will be selling for around $50.
It comes in a
20 pin 600 mil DIP package (small!) and consumes 48 mA at 3.6
to 24 volts.  It
has stereo input/output, 5 low speed ADC inputs (i.e. for
pots), 3 digital
outputs (i.e. for LED's), and analog and digital 3.3 volt
supplies to support
external circuitry.  It's easy to program and can be
loaded (EEPROM) using a
serial interface.  I have been updating some
postings on this at this forum:

http://www.diystompboxes.com/smfforum/index.php?topic84%359.0

If anyone is interested, has questions or comments/suggestions I'd love to
hear
about them!

Best Regards,
Mark Seel
Next Audio, Inc
snipped-for-privacy@gmail.com

      
                    
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Re: DSP Device for Guitar Pedal Effect


On Fri, 6 Nov 2009 10:26:46 -0800 (PST), Fred

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A XO a 22V10 and an EPROM?

Re: DSP Device for Guitar Pedal Effect


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I presume you mean a Programmable Logic Array.  I'm clueless about
them as well as FPGAs.  I lack any idea of how the arrays would/could
be programmed to do my non-linear transform.

Re: DSP Device for Guitar Pedal Effect


On Mon, 9 Nov 2009 09:17:21 -0800 (PST), Fred

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Actually it can be quite simple:  The incoming stream goes into a tiny
buffer (about 3 samples), the per sample mapping is looked up from
EPROM, the output value is sent to the next thing.

The 22V10 is there control that process.

Yeah, i know that is unclear.  But many other topics like state
machines get involved quickly and i think trying to discuss them here
may distract / bore others here.  My real email is in the headers,
Robert Baer and a few others have it as well.

Re: DSP Device for Guitar Pedal Effect



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Obviously.  ...even when the solution should be in hardware.
 
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Why wouldn't they fit?  Xilinx stuff has piles of RAM/ROM/dual-port
stuff.  The Actel and Altera stuff I'm using is just small enough that
there is no block-RAM.  I'd like to have it but for this application
don't really need it.  

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There is no reason all that stuff couldn't be done in hardware.

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C.  Ick!

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Spoken like a true software weenie.  There is a *tremendous*
difference.  You really should add another arrow to your quiver.

Re: DSP Device for Guitar Pedal Effect



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Part of the whole idea.  The more tools in your toolbox (all
reasonably well understood) the more and better tradeoffs you can make
between different approaches.
But then again i tend to be a specializing generalist.

Re: DSP Device for Guitar Pedal Effect



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Dunno about cordic -- to get that kind of speed from an inexpensive DSP
you probably need to go with something like a polynomial best-fit.  This
would make the "knob" adjustment easy, as you'd just change the
coefficients of the polynomial.

--
www.wescottdesign.com

Re: DSP Device for Guitar Pedal Effect



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Cordic algorithms have similar properties.
Besides there is nothing wrong or all that (time) expensive about a
post multiply.

Re: DSP Device for Guitar Pedal Effect



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Floating point at 100kHz?  Ick!

If you must do this with floating point you'll need a floating-point DSP
chip like an Analog Devices Sharc or a TI 6000 series ($$$, but maybe not
too much of a differential for a one-off).  I'd see if I couldn't do this
with a fixed-point chip and some sort of approximation, or clever fixed-
point math.  The design work is harder, but it may be worth it.

--
www.wescottdesign.com

Re: DSP Device for Guitar Pedal Effect



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I used an LPC2103 from NXP for a DSP project (partially floating
point). Worked like a charm without a single line of assembly. I doubt
you need 96kHz though. 44KHz will be more than enough.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
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