[mythtv-users] mythmusic iec958 help

Joe Henley joehenley at kc.rr.com
Sun Jul 6 15:54:17 UTC 2008


Mark,

It (pardon the pun) sounds like your set-up is working great.

But the bulk of the issues you've seen here are related to an original 
source sampled at 44.1KHz (CDRom) getting output thru the spdif into a 
receiver/home theater amp/etc.  The problem is that many sound cards 
(drivers) will re-code the signal as 48KHz.  This then causes the 
resultant output from the receiver/amp to the speakers to be shifted up 
in pitch about 10%.

For DVD (and IIRC, TV audio from a tuner card) the signal was originally 
sampled and coded as 44.8KHz, so there is no problem.  For alot of 
folks, there is no problem even with the up-pitch; especially if you 
don't have perfect pitch (hearing) or don't flip back and forth between 
the original signal and the "ripped-restored-spdif output" signal.

My hearing is none too great (just ask my better half), but I picked up 
the problem when I noticed an often listened to selection playing too 
"fast."  Then to see if I was just imagining the problem, I started 
flipping back and forth from the original CD to the ripped file of the 
CD.  Then it was very obvious.

If you, or someone who listens to your system, has perfect pitch, 
they'll notice it immediately; the pitch change more than the speed 
difference.

In a previous post to a similar problem, I mentioned I have no 
experience with the USB devices.  Your note sounds encouraging.  Please 
let us know which Creative model you're using and what the manual says 
about 44.1KHz spdif output.  If the USB "card" will output either 44.1 
or 48 KHz (and sometimes 32 KHz) the manufacturer will usually brag 
about it in the specs in the manual.  Please let us know; one of these 
USB cards would be a good option for lots of people.

Good luck,

Joe Henley


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