[sdiy] Digital audio demo on Youtube

Richie Burnett rburnett at richieburnett.co.uk
Tue Feb 18 20:58:07 CET 2014

Sinc interpolation, or a digital filter that closely models it, is the alternative. That's what most audio DACs from the last decade do internally.

There's nothing wrong with ZOH per say. It's just that it distorts both the waveform and the frequency response significantly, and then this really needs to be put right with a complicated analogue filter that follows.

The point Monty was making is that there is nothing inherent in digital audio that implies a ZOH should be part of the reconstruction. In fact it isn't the best method and actually leads to much confusion.


Sent from my Xperia SP on O2

cs80 at therogoffs.com wrote:

>I’ve read about the affects of ZOH using standard sample/hold DAC outputs but what’s the alternative?  In mathematical theory, the DAC output should be zero-width pulses whose area equal the sample value.  Do you have pointers to articles / part specs on DACs that try and approach this?
>There’s also DSD, but that’s a whole other can of worms and I assume that isn’t what you were talking about.
> David
>On Feb 18, 2014, at 11:16 AM, rburnett at richieburnett.co.uk wrote:
>> Monty's statement and Achim's reply are true.  The stair-steps are an artifact of the DAC designer's choice to use zero-order hold in their DAC.  The stair steps are not part of the digital sampled signal, they are the result of a design decision, just like the alternative options of linear interpolation, sinc interpolation, etc...
>> Zero-order hold distorts the wave shape, does very little to remove the high-frequency sampling images from the output, and also causes significant attenuation of the treble frequencies in the audio.  That's why consumer and professional audio DACs no longer use ZOH today.
>> -Richie,
>> On 2014-02-18 17:18, MTG wrote:
>>> I don't think this guy does any favours at 8:00 when he says that
>>> Wikipedia is confusing, "the stair-steps aren't really there". All the
>>> (non-1-bit) dacs I see in these old synths generate pretty visible
>>> stair steps... plus I'm sure there are lots of "control" dacs on the
>>> planet so we shouldn't just assume every DAC is on a PC motherboard
>>> (for instance).
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