[linux-audio-user] Sampling rate problems on a VXPocket v2

Geoffrey Martin GGM at bang-olufsen.dk
Thu Dec 11 04:07:17 EST 2003


I'm using the following:
      IBM T40 laptop
      Digigram VXPocket v2
      RedHat 9
      Kernel 2.4.22-ac4
      ALSA drivers 0.9.8
      vxloader 0.9.7-i686

Measurement gear
      Audio Precision System Two Cascade
      PrismSound DSA-1

Some of my other gear is having difficulties locking to the S/PDIF output
of the card at 44.1 kHz and I have a suspicion as to why this is

I have control over the sampling rate of the S/PDIF output of the card as I
would expect, however...

In the S/PDIF Channel Status Block information there is a portion of Byte 3
that is used to send the intended sampling rate (selectable between three
values, 32 kHz, 44.1 kHz and 48 kHz, depending on the arrangement of bits
0-3 in Byte 3. For specific information on this, please see Application
Note AN22REV2 from www.crystal.com). It is also possible, using bit 0 of
Byte 0, to indicate whether the signal is Professional or Consumer format.

Using my present configuration, I do not appear to have control over either
of these two variables. For example, even when I am sending a 44.1 kHz
signal at a rate of 44.1 kHz (or close enough... it's actually 44.0993, -17
ppm) Byte 3 of the Channel Status Block is saying that the signal is a 48
kHz transmission.

Are the VXPocket drivers in ALSA capable of changing these values in the
card? The official drivers for Mac OSX allow me to change the Pro/Consumer
flag using an application, and the sampling rate indicator changes
automatically with the actual sampling rate of the card's output.


Geoff Martin Ph.D.
Tonmeister, Bang & Olufsen a/s
email: ggm at bang-olufsen.dk
web: www.bang-olufsen.com
web: www.tonmeister.ca
phone: +45 96 84 49 54

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