[sdiy] Digital audio demo on Youtube

[Ingo Debus]

Am 18.02.2014 um 20:58 schrieb Richie Burnett:

> 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.

You guys are talking about distortion. What's your definition of distortion here? Distortion like in a guitar fuzz pedal? I don't think there's anything nonlinear going on here.

Look at it this way: transforming the ideal sampled signal (infinitely short nonzero values at the sample points and zero in between) to the real-world stair-step signal is nothing else but convoluting the ideal signal with a single rectangle with the length of the sampling period. Convolution in the time domain means multiplication in the frequency domain; and a single rectangle in the time domain corresponds to a sin(x)/x in the frequency domain.

So, going from time-discrete, infinitely short samples to a stair-stepped waveform means low pass filtering the signal, albeit that's a crude low-pass. But it makes the analogue reconstruction filtering easier, not more complicated.

Am I completely off?

Ingo