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Topic: Where did these (obsolete!) sampling rates come from?  (Read 1369 times) previous topic - next topic
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Where did these (obsolete!) sampling rates come from?

Some codecs came to offer them - was that "optimism" on some ultimately dying format's behalf, or ... ?

* 37.8 kHz and 18.9 kHz - that's 6/7ths resp. 3/7ths of 44.1 - were part of CD-i/CD-XA.
As ADPCM! I found one question on this forum, someone had apparently ripped it from a game CD.
37.8 found its way into the Musepack format. Was that for those signals, or were there others? And if it was for the CD-i/CD-XA for why not 18.9? (Was that dead already?)

* 7350 Hz sampling rate. That was in USAC in MPEG-D and also is one "standard" sampling rate in MPEG-4 audio.
Does anyone know the background and intended use? It equals a sixth of 44100, and I see no trace of there ever being any 14.7 (there is 16k which is a third of 48, so ...)

* 19.2 kHz and the double and the triple.  Apparently also in USAC in MPEG-D ... anyone?  57600 rings a modem bell, but if that were the answer, I would have expected to see the half rather than the third.


By the way, it is not hard do guess where 64, 128 and 256 kiloherz sampling rates came from - and yes 256 kHz is a thing in bat recorders (apparently that is enough to record all bats in Europe and North America) - but for more, that device supports 384 and ... 500 kHz. Why 500 and not 512, beats me, but it is not the only one: This seems to work at 500 kHz exclusively, and this one samples at 312.5, 384 and 500. The 312.5 must be for when this bat detector's sample rate of 307 kHz doesn't quite cut it.

Re: Where did these (obsolete!) sampling rates come from?

Reply #1
I would assume they are factors coming-out of a frequency divider from an pre-existing system clock.   Or maybe in some cases derived from the clock that generates video scan & frame rates.

Re: Where did these (obsolete!) sampling rates come from?

Reply #2
The CD-I format lets you interleave audio with data/images, with different audio formats providing different amounts of bitrate for the other channels.  My guess is the odd sampling rates (fractions of the CDDA bitrate) are to allow fixed amounts of bitrate to go to the other channels.

Re: Where did these (obsolete!) sampling rates come from?

Reply #3
Using .XA In PlayStation Development
https://psx.arthus.net/code/XA/XATUT.pdf

PlayStation 1 (PSX) supports different sample rates including 44.1kHz. It also has a synthesizer to support its own tracker format (PSF), so it has the ability to resample, pitch-shift, loop, mix, envelope and so on. PSX does not have built-in storage like HDD, and the CD-ROM drive is slow (2x?). Game saves are stored on proprietary memory cards with small capacity. I've seen some games used 18.9kHz audio when streaming some low-res lossy videos from discs, a format called MDEC, probably somewhat inferior to MPEG-1 used on VCDs.

Some big game titles like Xenogears occupy 2 CDs yet still can't afford using XA ADPCM as background music, many games used PSF to save space and loading time.

To go down the rabbit hole perhaps one can fiddle with some PSX emulators and game CD images.

The older Philips CD-i system on the other hand is much less popular than PSX, don't know if it has something to do with 18.9/37.8kHz or not.

Bonus reading for fun:
https://www.stereophile.com/content/case-jitters-less-cd-quality
https://archimago.blogspot.com/2013/03/measurements-sony-playstation-1-scph.html