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Explanation of 44.1 kHz CD sampling rate

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Re: Explanation of 44.1 kHz CD sampling rate

#21

Post by paulgerhardt »

jhallenworld wrote: post #8

This confuses me because the vertical rate is not 60 Hz, it's 3579545 Hz / (525/2 * 455/2) = 59.94 Hz. In other words it's odd that they would have chosen to be compatible with black and white instead of color.. instead of 44.1 KHz, it would be 44.056 KHz. Edit: Well it turns out that 44.056 KHz was used for the "EIAJ digital-audio-on-videotape standard" http://recordingtheworld.infopop.cc/eve/forums/a/tpc/f/22260...

Keen.

Sony was originally proposing 44.056 kHz (NTSC - popular in Japan) with 16 bits while Philips was pushing for 44.1 kHz (PAL - popular in Europe) with 14 bits. The two reconciled their differences at the 4th Red Book meeting in 1980[1]. Sony was further ahead in developing the CD players but Philips supposedly was in the lead when it came to making the CD's[2]. Sony insisted on 16 bit vs while Philips was pushing for 14 bit. As a compromise they may have gone with the 44.1 kHz Philips was proposing and the 16 bit Sony was proposing because it would be easier to remember. Posts [1] and [2] are in direct conflict with each other on this point. There was further tension over what size disc to use [2].

The CD was one meeting away from launching another format war in the spirit of VHS vs Betamax or Blu-ray vs HD-DVD

Of course 44.056 kHz products did make it into the field for professional audio engineers. Anecdotally this made for some trouble: http://www.realhd-audio.com/?p=2197

[1] http://www.exp-math.uni-essen.de/~immink/pdf/beethoven.htm [2] http://www.whathifi.com/blog/the-cd-is-30-years-old-today

Re: Explanation of 44.1 kHz CD sampling rate

#22

Post by guard-of-terra »

csense wrote: post #5

It seems strange to me that they would be re-purposing video tape for digital audio, given that digital tape technology was used in computers since UNIVAC in the 1950's [1]. [1] http://en.wikipedia.org/wiki/Tape_storage

Turns out you can store data on VHS too:

https://en.wikipedia.org/wiki/ArVid

Re: Explanation of 44.1 kHz CD sampling rate

#23

Post by cnvogel »

paulgerhardt wrote: post #21
jhallenworld wrote: post #8

This confuses me because the vertical rate is not 60 Hz, it's 3579545 Hz / (525/2 * 455/2) = 59.94 Hz. In other words it's odd that they would have chosen to be compatible with black and white instead of color.. instead of 44.1 KHz, it would be 44.056 KHz. Edit: Well it turns out that 44.056 KHz was used for the "EIAJ digital-audio-on-videotape standard" http://recordingtheworld.infopop.cc/eve/forums/a/tpc/f/22260...

Keen. Sony was originally proposing 44.056 kHz (NTSC - popular in Japan) with 16 bits while Philips was pushing for 44.1 kHz (PAL - popular in Europe) with 14 bits. The two reconciled their differences at the 4th Red Book meeting in 1980[1]. Sony was further ahead in developing the CD players but Philips supposedly was in the lead when it came to making the CD's[2]. Sony insisted on 16 bit vs while Philips was pushin…

Quoting your first link [http://www.realhd-audio.com/?p=2197]...

❝Of course, lots of CDs were released with the original 44.056 kHz rate simple reclocked at 44.1 kHz. This resulted in a very slight speed increase AND a pitch shift of less than a quartertone.❞

While technically true (less than a quartertone), it's much, much, much less than a quartertone. It's 1.7cent (1.7 percent of a half-tone, or 1/30th of a quartertone). If you accidentally mix up 48kHz and 44.1, it's a much more noticable 1.5 half-tones. I doubt that this slight detuning is so blatantly obvious that it "feaks out" even a very well trained and very hot tempered classical violinist.

If you want to check the math: There are 12 semitones in an octave. One octave doubles the frequency, so the frequency difference between two adjacent semitones (e.g. from any key on your piano to the adjacent white or black key) is the twelfth root of two: ~1.0595. When tuning your guitar, your tuner might display the deviation from the true tone in cents, that's 1% of the interval between two halftones, or (python) math.pow(2,1.0/12.0e2) -> 1.0005777895065548.

Frequency ration between 44.1 and 44.056 kHz is 1.0009987.

Re: Explanation of 44.1 kHz CD sampling rate

#25

Post by noonespecial »

asimpletune wrote: post #24

How does this make it to the top page?

I can't say for anyone else, but for me, I was an AV nut in the old days. I remember pulling apart an early Sony CD player in '89 or '90 and screwing each part down on a piece of wood so I could reach everything and looking at every single trace with my "new" old Phillips oscilloscope trying to understand the magic.

These stories are like finally getting to see the cards from a game long over. Pure gold to me. Upvoted.

Re: Explanation of 44.1 kHz CD sampling rate

#26

Post by anyfoo »

asimpletune wrote: post #24

How does this make it to the top page?

This is exactly what I want to read on Hacker News. Some people come here for the posts about startups/founder culture (I don't, but I fully accept that it's part of the site), some because of the highly technical posts. It's probably beneficial in some way that Hacker News is a mixture of both.

Re: Explanation of 44.1 kHz CD sampling rate

#27

Post by ArkyBeagle »

csense wrote: post #5

It seems strange to me that they would be re-purposing video tape for digital audio, given that digital tape technology was used in computers since UNIVAC in the 1950's [1]. [1] http://en.wikipedia.org/wiki/Tape_storage

Video tape was vastly less expensive than tape drives used for nine track data storage and all. You could actually buy a decent Beta or VHS machine for 1) less than $2k for a while and 2) less than a kilobuck later ( before DVD drive it down ) .

Re: Explanation of 44.1 kHz CD sampling rate

#28

Post by ArkyBeagle »

nullc wrote: post #13
ar7hur wrote: post #2

Also, the fact that 44,100 can be factored as 2^2 * 3^2 * 5^2 * 7^2 makes it very efficient to do Fast Fourrier Transforms on moving windows. Which we do a lot in Speech Recognition and DSP in general.

Actually 44.1kHz is unhelpful for that... a lot of infrastructure exists that expects things to work on 10 and 20ms intervals (and multiples there-of), e.g. the normal windows audio apis work in 10ms chunks. 10ms of 44.1kHz is 441 samples, which is odd and thus a not really fantastic size for easily implemented factorizations. Of course, if you can pick your own analysis interval you can pick some nice power of two o…

10-20 msec is the neighborhood of the Haas Limit. That's why, sfaik.

Re: Explanation of 44.1 kHz CD sampling rate

#29

Post by ar7hur »

recursive wrote: post #20
ar7hur wrote: post #16

Earlier quoted context omitted.

What you say actually makes no sense whatsoever. Why are you talking about 1 second windows? If 44100 can be decomposed easily in small prime numbers, it means that you can split 44100 into windows that are themselves products of small prime numbers.

Why are you splitting 44100 samples into windows? That's the number of samples in one second. Where did you get one second from? You could have started from any duration.

I see what you mean, but since the 1970s speech researchers have been splitting seconds into 10ms or 25ms intervals, that's not my decision. They could have started from any duration but they haven't. And you could start to express time with the Aztec calendar if you wanted. But you won't.

Re: Explanation of 44.1 kHz CD sampling rate

#30

Post by smackfu »

masklinn wrote: post #11
bartekko wrote: post #9

This has already been posted to HN before, but its the best explanation of digital audio I have seen: http://xiph.org/video/vid2.shtml

http://xiph.org/video/ is probably a better link, the first episode has plenty of interesting and important stuff.

Also on Youtube: https://www.youtube.com/watch?v=Ny7krNFAD1s&feature=kp
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