help with ADC and DAC

[tekzilla]

I know these aren't used in guitar wiring, but i figured someone out there might know if what I want is possible or not.

I want to have an 8-bit analogue to digital converter and a digital to analogue converter in my guitar so that it gives a Nintendo type lowfi sound.

[ashcatlt]

Welcome!

I personally shy away from onboard effects. I have, however, always wanted a digital distortion pedal. I'm thinking more about actually clipping the ADC. Would be cool if it had some form of digital gain as well, so you could clip the signal after it's been converted to bits. Of course, bit/sample rate controls would also be required.

I haven't done a whole lot of research on it. I can just barely handle some simple analog circuits! I have noticed, though, that most of the "Bit Crushers" out there are either analog emulations or are actually more like sample rate converters. I did find this, which might get you a little closer.

[ChrisK]

This isn't especially difficult to do from the hardware perspective (AD converters/DA converters). It's more difficult in that a microprocessor may be needed. There are few ADs and DAs that just automatically work together.

The hard part is the embedded software.

Stating that you want to use an 8 bit AD/DA indicates that you sense that the lack of resolution alone is enough to give a low-fi sound. I would mention that using 8 bits for either the AD or DA will effectively limit the resolution to 8 bits.

Another component of this sound is the aliasing created by the decimation/sampling rate. Nyquist's Sampling Theorem indicates that a frequency (harmonics are frequencies too) must be sampled at least 1.9 times the frequency to discern that frequency independent of phase. Under-sampling in a time-base manner will result in the loss of any frequency component above said threshold, but the granularity induced by the low AD/DA resolution will induce harmonics of the input/output sampling rate(s) that are not harmonically related to the frequencies from the strings. Discordant is the operative word.

This is why CDs have a DA/output update rate of 44Khz.

My point is that, if one wants to produce certain expected effects, there is a whooooooooooooole lot more theory and math to be applied. Sorry.

If one just wants to mess around, I'd recommend that one take a tour down the "BASIC Stamp" lane a'web. You need something with both AD and DA or you have to get into embedded controller design. You also need a stamp that has a high enough sampling rate to even get to low-fi!

It's complicated. I know. I've done embedded controller design for a career.


{One may get similar results by using an integrator-based hysteresis comparator(s) and a summer, or a decimating sample/hold amplifier. Copyright 2008 CEKikta}

[tekzilla]

Wow, I was thinking that some problem must exist. I really just wanted to know if it was as easy as an ADC into a DAC or not.

Chris, I didn't know what I wanted to do was sampling, or is that only with the microprocessor? Oh! and is there any way I could use an old soundcard as my powered DAC? Because I know how much power to give it, and then I just need to give it a digital signal and use its audio outs right?

See I have all these Ideas, but I have no circuitry skills.

Thanks for the links though guys, theres enough for me to learn for a while here.

[sumgai]

Chris,

How you gonna copyright the flash conversion of a Schmitt trigger (or a series of them)?


sumgai