[sdiy] A/D --> D/A conversion and audio

[phillip m gallo]

Bret,

I don't know about the 'Mega converter but, thinking  generically, there
is a lot you haven't mentioned:

1) Are you driving the 12 bit output DAC at the same sample rate of the
input ADC?

2) As there is no input circuitry, how the does the input relate with
the spec's for the ADC? For instance is the A/D "bi-polar" accepting +/-
inputs or uni-polar ? If uni-polar you are going to have to bias the
audio to 1/2 of the ADC acceptance range .

3) The signal swing of the Audio? Is it scaled to use the maximum bit
range of the A/D Converter ?

4)The numeric formats of the ADC and DAC.  Are they compatible?

At 40KHz with a 12 bit output you should be able to render pretty decent
audio for playing around.  If your converter exceeds the bit width of
the DAC be sure to "round" not truncate the unused LSB's. 

regards,
p
 

-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of Bret Truchan
Sent: Saturday, January 03, 2004 3:23 PM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] A/D --> D/A conversion and audio



Hello!

So, I've wired up this very simple circuit and I could use a little
advice.  
I am using a Atmel Mega 16 microcontroller that has A/D inputs.  I'm
taking 
an audio signal directly into the A/D converter and sampling at around >
40k 
hertz.  (I think!)

I'm then outputing the results of the A/D to a D/A converter (DAC7625P),
and 
from that into my mixer.

It's working to the point here I can hear the music, but there's a lot
of 
digital degradation going on.  I've posted some questions to the Atmel
AVR 
site and have gotten some good advice, but none that has cleaned up the 
audio.

I'm curious.  I don't have any circuitry between my audio source and my
A/D 
input.  Does that mean that I'm clipping the negative voltages out of my

source?  That seems like it could cause some distortion. :-)  This is my

first time trying to do A/D conversion on audio!!

Thanks!!
- Bret

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