[alsa-devel] iec958 switch uneffective while playing ac3 stream

Dominique Dumont domi.dumont at free.fr
Mon Mar 26 21:03:46 CEST 2007

Dag Lem <dag at nimrod.no> writes:

> That is probably caused by the following setting in
> /etc/alsa/cards/HDA-Intel.conf:
> name "IEC958 Playback Switch"
> lock true

Got it. Thanks for the tip.

> IIRC the lock setting is effective if you specify the device
> "default" or "iec958", but not if you specify "hw:0,1". I assume
> this is why you get different results with PCM and AC3 playback.


I've also used iecset to switch the audio/non-audio bit while playing
an AC3 stream with 'ac3dec -C -D hw:0,1'.

With 'iecset audio mode true', I can hear the typical shuf-shuf-shuf
of an ac3 stream played "raw" and the 48KHz Frame rate is shown by my

With 'iecset audio mode true', the sound shuts off and the 48KHz
indicator is removed from my amp display.

So I assume that the AC3 stream is garbled somewhere. 

According the HDA doc, the same stream settings must be sent to:
- the HDA controler 
- the converter (verb 0x200)
- the digital converter (verb 0x70D 0x70E)

So far I can't see anything wrong with the converter or the digital
converter. Except may be the converter's PCM bit 15 set to PCM instead
of non-PCM. (But I've changed it to no avail :-( )

The only thing I've not verified is the HDA controler stream
setting. I still have to find where it's done :o)


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