[Noisebridge-discuss] [noisebridge-discuss] HELP: Audio playback via uC, Sampling, pwm-DAC

[Robby]

Sorry, I sent this to jake instead of discuss: I got it right guys, i was
writing to the wrong pwm compare register! sorry for the false alert.

On Sun, Jul 8, 2012 at 12:59 PM, Robby <robwasab at gmail.com> wrote:

> Hello y'all,
> I'm depressed, see, I can't get my micro to play back recorded audio
> samples, here's what I've been doing and from what I can tell, the internet
> says todo:
> using an tiny85 I'm using its 64Mhz PWM with a low pass filter to create
> analog voltages, I can create a sine wave using a 256 byte lookup table I
> use 256 resolution because I do this:
>
> OCR1B = pgm_read_byte[sinWaveTable + TCNT0]; //The timer speed is the
> speed at which the wave table is played back
>
> And it makes a really good sin wave (used an oscilloscope to verify this).
>
> however, this shows that I can create relatively good analog voltages, I
> cannot play back sounds that I've saved in the avr's flash.
>
> to do this, I have converted an arbitrary sound file to .WAV
> (uncompressed) further converted it to 8bit sampled at 6khz. So each byte
> in this file corresponds to a sinusoidal sound wave point, and all i have
> to do is play back each analog value at the speed of the sampling rate.
> (please verify me on this?) makes sense. I open the WAV file in a java
> program that I wrote that reads each byte and separates them with commas so
> that I can make an array out of the data.
>
> And I just play it back, I tried to use a Compare Match A interrupt to
> read each array value (at the sampling rate hence the compare match
> interrupt) and change analog value coming out of OCR1B but it sounds like
> SHIT, I can't even tell what it sounds like.
>
> If anybody has had experience with this approach maybe you can help me?
>
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