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Comment by layoutIfNeeded | Hacker News Reader

Sigh... No, digital signals are not “square waves”. https://youtu.be/cIQ9IXSUzuM

I always laugh when vinyl is described as more “pure”. There’s nothing more pure than math, and that’s digital PCM audio. Sure, it’s stored as discreet samples, but that’s not how it comes out of speakers. The digital->analog converter will give you 1:1 perfect representation of the original waveform as long as you sample at 2x the highest frequency desired and there’s a low-pass filter in place.

Have you ever played with an Arduino or similar device? Comparing inputs signals on a digital pin vs an analog pin? Hopefully, you'll agree it's the same concept. If you haven't, I'd encourage you to try one out. They are loads of fun. I am a huge fan of analog, yet digital is just so damn convenient. If you have played with one, you'll understand why your comment makes me smile and chuckle.

A digital pin will most likely output a signal using a zero-order hold, which is the simplest type of reconstruction filter.

A zero-order hold is just one possible way of turning a digital signal into an analog one which you can then measure with your oscilloscope. But the output of the zero-order hold is not the digital signal, because the digital signal is only defined at discrete sample points.

Not strictly true, you must sample at 2x the frequency and at sufficient resolution in the amplitude domain, i.e. an ADC that samples at 44 kHz but with only one bit of resolution (outputs a 1 for positive input voltage and 0 for negative, say) would be pretty awful...

On the other hand a sigma-delta ADC that samples at 2.8 Mhz with only one bit resolution is pretty good (for audio purposes).

With sigma-delta modulation you can trade sample rate for bit depth and vice versa.

For the record, I don't think vinyl enthusiasts ever describe vinyl audio as more pure. "Pure analog," yes, but that's different (and true). It's generally acknowledged by vinyl enthusiasts and audiophiles that vinyl introduces a lot of imperfections, which some people prefer.

Also worth noting that an ideal D/A converter will give you the exact waveform back, but such a device does not exist (but you can get pretty close).

Your comment might be more helpful (i.e. more likely to be read by others who could use the information you're providing) without the snark.

Sigh... you are wanting to show me that we can do A/D and D/A again? Thanks, I was totally unawares that we could do that. I've never heard an audio signal played back once it was digitized. My life is now complete.

What this guy is showing is not a digital signal. It is an analog signal that has been generated from digital data. Not sure what the point of all of this was, but thanks, I needed a break from finding this bug I've been trying to squash.

I recommend watching the video again, all the way through -- no skipping. It's pretty great.

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