[sdiy] I2C DAC

Tom Wiltshire tom at electricdruid.net
Tue Jun 22 11:53:01 CEST 2010

The main effect of the oversampling as far as I understand it is to  
move the DAC convertor quantization noise further out of band. If  
you've got a 48KHz sampling frequency, the quantization noise is a  
nasty looking ramp-like waveform at that frequency. Whilst you can  
filter that out reasonably well with post-DAC filtering, it's a lot  
more effective if you interpolate and increase the sample rate so  
that the quantization noise is at a higher frequency.

So, no, you don't gain any data, but you do reduce the noise.


> I've been looking into DACs lately with regards to Audio vs Control.
> From what I understand the main difference is that audio DACs have
> interpolation filters built in to reduce out-of-band spectra.
> They also oversample to place the frequency of the "image" that
> creates inverted copies of the signal into a region that makes it
> easier to filter down-line.
> Would I be correct in saying that these features are more important
> when playing back sampled material vs generating signals like a  
> digital OSC?
> Oversampling a 12bit sine wave at x256 that is 48kHz and
> interpolating between steps and then outputting at the same sample
> rate 48K does not create any new data..or does it.
> Would the sound be any better using an audio DAC vs a voltage out
> control type dac given the same sample rate and bit depth?
> These are the questions I ask myself.
> The main reason is that audio DACs nead an I2S or codec interface and
> that is a lot more difficult to find than a SPI port on many uC.
> Bruce

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