DSP Device for Guitar Pedal Effect - Page 3

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
Re: DSP Device for Guitar Pedal Effect


On Sun, 25 Oct 2009 20:26:21 -0700 (PDT), Fred

Quoted text here. Click to load it

If you want trig functions it may be DSP/FPGA only.  They take lots of
CPU to compute.

Re: DSP Device for Guitar Pedal Effect


On a sunny day (Sun, 25 Oct 2009 19:46:54 -0700 (PDT)) it happened Fred

Quoted text here. Click to load it

Whatever you choose, keep in mind that digital processing introduces delays.
'Latency' is the word.
That may cause very undesirable effects in the end result.

So a bleeding fast DSP should be at an advantage here (read power guzzling).
Or maybe do some of the processing in hardware, say use an FPGA.
Depends on all you want to do.
Maybe an analog circuit makes more sense for a guitar...
But then again if your name or preference in Jimmy Hendrix., maybe all the
artefacts will help a bit ;-)
grin



Re: DSP Device for Guitar Pedal Effect




Fred wrote:

Quoted text here. Click to load it

I am going to build Space Shuttle. It uses diodes. Would 1N5404 be a
good diode for Space Shuttle?

VLV

Re: DSP Device for Guitar Pedal Effect


Quoted text here. Click to load it


No, a 1N3712 would be *far* better for traveling through time and space,
especially if you encounter wormholes along the way :-)...

Regards,

Chris

Re: DSP Device for Guitar Pedal Effect


On Mon, 26 Oct 2009 09:36:40 -0500, Vladimir Vassilevsky

Quoted text here. Click to load it

No.  It is not fast enough.  ;3D%P20%

Re: DSP Device for Guitar Pedal Effect



Quoted text here. Click to load it

While you're doing tradeoffs, consider a cheap FPGA.  It may be a good
fit, particularly if your intended processing is memoryless.

--
www.wescottdesign.com

Re: DSP Device for Guitar Pedal Effect


Quoted text here. Click to load it


I'd drop the 96kHz requirement to half that. At most. For guitar,
an Fs of 20Khz might be good enough. You might be able to proto the
thing in a VST plugin.

--
Les Cargill

Re: DSP Device for Guitar Pedal Effect


Quoted text here. Click to load it

There are many good reasons to oversample. It is always used in medium to
high end digital audio stuff nowdays. (mainly because most pro audio ADC's
do it) Generally it helps with writing better and more accurate filters.

Mainly it fixes the problems of aliasing. If you sample and audio signal
then you need to have either a very sharp analog filter at, say, 20khz or a
very gradual one at, say, 1Mhz with 10x oversampling. Then you can write
better digital filters for the sharp filtering. It is easier for to create a
sharp digital filter than an analog filter if your doing other digital
processing.

Basically by oversampling your moving the need for sharp filtering from the
analog side to the digital. All it really boils down to is initially
treating the input as if it had a much higher bandwidth.

The point here is that actually it is generally better(Cheaper and more
accurate) to sample an audio signal upwards of 1Mhz.  Of course it requires
more processing power unless the ADC does this internally.





Re: DSP Device for Guitar Pedal Effect


Quoted text here. Click to load it

I'm vainly trying to imagine why a guitar pedal would need a sharp
filter *internally*.... they're generally collections of allpass
filters at the most sophisticated.

You'll get well-oversampled D/A and A/D anyway, which is where the
steep ones are needed.

All I'm saying is that electric guitars obey a relatively modest
bandlimit. Not all of them, mind you - a Firebird or Danelectro
can throw 30KHz.

And it might be worthwhile prototyping as a VST to find out what you'd
lose moving the bandlimit down. And the interest in moving the bandlimit
down is to use a more modest CPU for the actual effects processing - big
cost driver and power sucker.

Quoted text here. Click to load it

They do, at least any I'm even remotely familiar with that would be
appropriate. And I'm really at least five years out of date - I imagine
the world has moved on.

Quoted text here. Click to load it

--
Les Cargill

Re: DSP Device for Guitar Pedal Effect


Quoted text here. Click to load it


You don't understand. It's not necessarily from the guitar(the guitar has
it's own low pass filter). Any signal that might get on the line(from
radiation or whatever) can be aliased back if not filtered.  This is always
the case what ever the source. You must filter before sampling or you will
get aliasing of the higher frequencies(above the nyquist) into the frequency
band your after. (in fact this can be useful in some cases)

The guitar's bandwidth maybe, say, 15khz so you sample at 30khz. The guitar
is bandlimited because of filtering(assuming it has one) but any noise on
the line that introduces frequencies above 15khz will be aliased back into
the signal(and effectively be part of the signal). A very sharp low pass
filter at 15khz would take care of all that since it will remove any
potential for aliasing(except any created between the filter and the ADC or
in the ADC).





Re: DSP Device for Guitar Pedal Effect


Quoted text here. Click to load it

No, I gotcha. Audio-oriented DAC/ADC are generally going to support
20Hz to 20KHz well no matter what, though. Aliasing reall isn't a
consideration, unless the transform within the GPP in the middle
somehow causes it.

--
Les Cargill

Re: DSP Device for Guitar Pedal Effect




Les Cargill wrote:


Quoted text here. Click to load it

Aliasing is a BIG problem if doing non-linear audio effects in digital.
You want the sample rate of 192kHz or even higher.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

Re: DSP Device for Guitar Pedal Effect


Quoted text here. Click to load it

Yep, and my effect will be non-linear.

Re: DSP Device for Guitar Pedal Effect



Quoted text here. Click to load it

Depends on the A/D D/A converter. All the codecs (A/D D/A converter in
one chip) I encountered so far have decent anti-aliasing filters
built-in. Aliasing shouldn't be a problem.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
We've slightly trimmed the long signature. Click to see the full one.
Re: DSP Device for Guitar Pedal Effect




Nico Coesel wrote:

Quoted text here. Click to load it

It is unrelated to A/D and D/A. If you do a nonlinear function with
already sampled signal, you will get aliasing.

Let's say there is a sine wave at 10kHz, and a 48kHz ADC -> digital
limiter -> DAC system. At the output, you will get 18kHz, 2kHz, 16kHz
and so on, so forth.

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com









Re: DSP Device for Guitar Pedal Effect


Quoted text here. Click to load it

That's just about the picture.  The Spin chip has 48kHz converters.
So, it'll be:

48k ADC > Digital Compression > 48k DAC.

What I am wondering about is hearing the aliasing.   In the early CD
players I could hear it.  In low quality digital effects like delay
and reverb I can still hear it.

Re: DSP Device for Guitar Pedal Effect


On Thu, 29 Oct 2009 16:15:47 -0700 (PDT), Fred

Quoted text here. Click to load it

I am not sure about what you hear (heard), but a lot of early CD
players had lousy DACs.  Lousy converters could be the problem in the
early cheap effects devices.  It is a very different sonic effect than
aliasing.  Then there are/were converters that lost resolution (ENOB)
at higher frequencies (like 10 kHz).

Re: DSP Device for Guitar Pedal Effect


On Thu, 29 Oct 2009 15:39:07 -0500, Vladimir Vassilevsky

Quoted text here. Click to load it
No, not really.  Not unless you are saturating the input ADC.  If you
do that all bets are off (so to speak).

Re: DSP Device for Guitar Pedal Effect




JosephKK wrote:

Quoted text here. Click to load it

Huh?
Run the numbers.

Quoted text here. Click to load it

That has nothing to do with DAC and ADC. Once you do nonlinear functions
in digital domain, you get aliasing.

If you apply nonlinear function to a perfect digital sine wave, you will
get harmonics. If those harmonics are above Nyquist, they will be
aliased down.

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com







Re: DSP Device for Guitar Pedal Effect



Quoted text here. Click to load it


The successful ones like Line 6 are believed to increase the sampling rate
before applying the non-linear function (i.e. upsample) and then LPF whilst
downsampling; see
http://www.mitpressjournals.org/doi/pdf/10.1162/comj.2009.33.2.85?cookieSet=1 .
Some (perhaps many) of their effects use ADC/DAC working at about 39 kHz
sampling rate and they don't have a reputation for sounding bad.

Chris



Site Timeline