[mythtv-users] Myth, Jack & resampling
Dave Badia
dbadia at gmail.com
Sun Jul 6 02:23:35 UTC 2008
>
> This sort of technical topic is one that seldom seems to get covered
> correctly in things like Wikipedia. To give Mark Greenwood credit, he
> did use "standard" whereas you did not. None the less you both have
> good points:
>
> 1) Digital audio can be managed at any frequency. Think about 8KHz mp3
> files. That's 'digital audio', but it's not 'sound'. CD's are 44.1K.
> DVD's are 48K (I believe) mp3's are all over the map.
>
> 2) Digital *interfaces*, such as coaxial spdif, optical spdif, optical
> ADAT, HDMI, etc., can generally run at different frequencies. I use
> coaxial spdif and optical ADAT every day at 44.1K through Jack. I use
> optical spdif on my home theater receiver at 48K. Both work great, and
> it's all completely contemplated in the original hardware interface
> specs, but I have hardware to support it. (This hardware also supports
> 88.2KHz, 96KHz, and external clocking if I want to run at some other
> custom frequency.) However those same spdif hardware interface specs
> to *not* require that devices support all frequencies. That's left to
> the implementation so I don't think the device you speak of is
> necessarily 'out of spec'.
>
> 3) Many recent PCs have seemingly opted for fixing hardware sample
> rates to 48K in favor of DVD playback. There are lots of sound cards
> that cannot change frequency and therefore *require* software
> resampling of at least one format into the other. Most folks don't
> know how to check for that before they purchase, nor would it likely
> change their purchase if they did.
>
> 4) I personally don't know of any PC sound cards that resample in
> hardware as to do that really requires that card has both clock rates
> available which adds cost and is of little value to 99.9% of their
> owners.
>
Thanks for the info Mark, this is all very helpful.
> I've been interested in this thread as I've never bothered to try Myth
> through Jack, and then beyond that through Jack running with real-time
> priorities. Hope this response adds another (hopefully useful)
> perspective to the conversation.
>
> Cheers,
> Mark
>
During these experiments, I've been running myth through jack with jack
running at real-time priority. All seems to be working well, I even
introduced jamin (EQ) into the equation, everything worked well, pretty
impressive stuff.
Dave
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