[sdiy] I2C DAC

[Bruce Duncan]

Thanks guys..great information.
I wasn't getting the complete picture on the benefits of the audio dac.

I am not trying to recreate the PPG sound so I will try and get a 
non-instumentation dac working on this one.
I am band-limiting synthesized waves by using additive sine technique 
so no ugly square waves here hopefully.
I used to have an Ensoniq EPS which was 12bit. Wonder if it used an 
interpolating dac?

Thanks
Bruce



> > 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.
>
>I am not sure what you refer to, but I don't know any conversion
>device in which a signal is oversampled and then immediately
>downsampled.
>- Sigma-delta converters internally oversample (interpolate) the
>signal in the digital domain to generate a high-speed 1-bit stream
>which approximates the original signal once low-pass filtered.
>- Some "traditional" (ie not 1 bit internally) converters might
>oversample to get more resolution or to make reconstruction filtering
>easier (the internal oversampling makes the steps finer and easier to
>filter: you don't need a super steep filter to remove the aliasing).
>
>I don't see how there would be a difference between synthesized audio
>and samples read from a ROM. None of them are meant to contain data
>above sr/2, so both of them will need a reconstruction filter.
>
>However, if you're after the sound of early digital synths (PPG,
>Prophet VS...) you'd better go with the rawest control/instrumentation
>DACs - because those early machines did not have reconstruction
>filters - which would have been tricky to implement I guess on devices
>like the PPG wave in which sample transposition is achieved by
>adjusting the clock rate rather than resampling (source:
>http://www.vintagesynth.com/sci/birth.txt,
>http://www.electricdruid.net/index.php?page=info.wavetableoscs). And
>no, a SSM2044 doesn't count as a reconstruction filter ;)
>
> > 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?
>
>Might depend on what kind of "fidelity" (high fidelity to the
>"theoretical" waveform, or high fidelity to classic digital synths)
>you're after!
>
>Another thing: more than DAC quality, something that will directly
>impact the quality of your synthetic waveforms is whether they are
>band-limited or not in the first place. If you work at 48kHz,
>(square_output = phase_counter_16bits < 0x8000 ? 0 : 4095) is going to
>sound ugly no matter what kind of DAC you put behind.
>
>Olivier