Digital Audio - the signal theory - Page 1
Forum section: electronics / beginners

author: DrGeoff
author_rank: Frequent Contributor
timestamp: November 07, 2015, 04:47:44 am
content: A great video describing digital audio from a signal theory perspective, and why there are so many myths surrounding sample rate and bit depth, nyquist and dithering.Not something an Audiophool would want to watch though

author: PChi
author_rank: Frequent Contributor
timestamp: November 07, 2015, 03:50:11 pm
content: Thanks for the link, it's an interesting and well presented video. The explanations and tests do rely on the A/D, D/A, anti aliasing and reconstruction filters all being properly designed. Somthing that can't be relied upon in Audiophool electronics.

author: Kalvin
author_rank: Super Contributor
timestamp: November 07, 2015, 03:54:54 pm
content: Quote from: PChi on November 07, 2015, 03:50:11 pmAnd the perfect signal will be eventually destroyed by loudspeakers and crossover filters, if not in the amplifier.

author: DrGeoff
author_rank: Frequent Contributor
timestamp: November 07, 2015, 09:52:38 pm
content: Quote from: Kalvin on November 07, 2015, 03:54:54 pmOr, more likely, by the room itself. You can spend as much as you like on all the components, but if the room is not properly designed and treated then the acoustic performance will be rubbish.

author: SteveLy
author_rank: Regular Contributor
timestamp: November 08, 2015, 08:12:35 am
content: Thanks for the post. It's good stuff and true. Wish the guy did not disable youtube comments.Many folk unpappy about audio digitisation don't think of the digitised signals converted back to analog as piecewise continuous steps but as linearly interpolated connect-the-dots signals (just like an oscilloscope displays waveforms in non-interpolated "vector" mode). Hence the belief that well-beyond-Nyquist-sampling will make for a more accurate reproduction because when you make a connect-the-dots plot, the more dots the merrier.The Nyquist sampling theorem is a mathematically robust one and most audio hobbyists don't appreciate how rock-solid irrefutable it is. But its advocates (including the guy in the video) also underplay the stringency of the underlying assumption that the input signal is bandwidth limited. An old vinyl record may be analog bandwidth limited to ~15 kHz, but the signal vs frequency fall-off is not infinitely steep. There is still signal there well beyond the Nyquist cut-off and that will either be lost (which is usually okay) or more likely, with sloppy AD conversion techniques, show up as aliasing artefacts in the digitised signal.Digital is as good and better as analog when done right. But sometimes it's not done right.

author: kripton2035
author_rank: Super Contributor
timestamp: November 08, 2015, 08:37:32 am
content: instructive video - thanks.

author: EEVblog
author_rank: Unknown
timestamp: November 08, 2015, 09:31:39 am
content: Quote from: DrGeoff on November 07, 2015, 04:47:44 amDamn that's a well produced video.

author: DrGeoff
author_rank: Frequent Contributor
timestamp: November 08, 2015, 10:02:47 am
content: Quote from: EEVblog on November 08, 2015, 09:31:39 amIsn't it just. The whole equipment setup is brilliant for demonstration. I particularly liked the shaped dithering demonstration.

author: EEVblog
author_rank: Unknown
timestamp: November 08, 2015, 10:19:45 am
content: Quote from: DrGeoff on November 08, 2015, 10:02:47 amIt would have taken a hell of a lot of time and effort to produce that video.Small things like the strategically placed walks across camera to simulate a video wipe was a nice touch.Studio quality lighting, framing, and sound tooYes, the interactive dithering demo was superb.

author: SteveLy
author_rank: Regular Contributor
timestamp: November 09, 2015, 02:16:28 pm
content: The guy is a Red Hat engineer.Not Microsoft Research.And it shows.

author: coppice
author_rank: Super Contributor
timestamp: November 09, 2015, 02:33:40 pm
content: Quote from: EEVblog on November 08, 2015, 10:19:45 amHe has a few other similar quality videos on related topics.

author: Delta
author_rank: Super Contributor
timestamp: November 09, 2015, 02:48:19 pm
content: I spotted that video a while back, it really is superb.It should be compulsory viewing for all audiophools...

author: tooki
author_rank: Super Contributor
timestamp: November 09, 2015, 03:49:01 pm
content: I have for years now said that that video is required viewing for anyone who starts talking about digital audio in any way. I really hope he makes more videos.I am not surprised at all that comments are disabled. Imagine the audiophools coming out to downrate it and post silly comments about how the cables, err, "interconnects", weren't insulated in Rapunzel's hair, etc.

author: SteveLy
author_rank: Regular Contributor
timestamp: November 09, 2015, 05:38:26 pm
content: Reading the description to the youtube vid, I reckon comments are disabled because the uploader is not the author. Original here:https://www.xiph.org/video/