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View Full Version : L/R channel swap status?



Phillip Kerman
2004-09-09, 21:30
This bug is driving me nuts. I'll bet it crops up for a lot more people but
they just don't notice it. I only sometimes notice something's weird and
then check it and find it's backwards.

What is the status of this bug?

What do you need me to do to help it go away?

Thanks,
Phillip

seanadams
2004-09-09, 21:44
Phillip,

I've got some more info on this. It only happens on the s/pdif output,
and is introduced when switching from mp3 to non-mp3 formats. The
easiest workaround for now is to use analog outs instead (I know, I
know).

Another workaround is to have all your audio decoded to PCM and this
will prevent the mp3<->pcm mode change which triggers this. Somebody
posted a convert.conf entry to do this a couple days ago.

It's definitely a bug in the DSP software (not the server) and I am
working with our vendor on a fix.

Sean

On Sep 9, 2004, at 9:30 PM, Phillip Kerman wrote:

> This bug is driving me nuts. I'll bet it crops up for a lot more
> people but
> they just don't notice it. I only sometimes notice something's weird
> and
> then check it and find it's backwards.
>
> What is the status of this bug?
>
> What do you need me to do to help it go away?
>
> Thanks,
> Phillip
>
>

Mike Reeve
2004-09-09, 22:22
Sean Adams <sadams@...> writes:

> and is introduced when switching from mp3 to non-mp3 formats.

Sean

A small comment/suggestion:

Until you recently suggested that I tried an MP3 track
followed by an uncompressed AIFF/WAV track
as part of the bug tracking process
I had never (ever) played an MP3 track on my Squeezebox before.
BUT I had regularly seen the L&R channel swap ...

Starting from your analysis above
would lead one to presume that
the DSP is currently set up to start up in MP3 mode
and us uncompressed/lossless-only users hit the bug
because as soon as we start to play any of our tracks
it switches from MP3 to 'raw PCM' ...
SO, if it is the case that the default start up mode is MP3
then a short-term fix for us uncompressed/lossless-only users
would be to have the default start up mode be 'raw PCM'
- assuming that this is under your control
and not built in to the POR microcode of the DSP.

[Although (out of curiosity),
why is the channel swap clearly only itermittent ...? :-O]

Regards

Mike

seanadams
2004-09-09, 22:47
>
> SO, if it is the case that the default start up mode is MP3
> then a short-term fix for us uncompressed/lossless-only users
> would be to have the default start up mode be 'raw PCM'
> - assuming that this is under your control
> and not built in to the POR microcode of the DSP.

mp3 is the startup mode and then we download some software into the dsp
to make it do PCM passthrough.

> [Although (out of curiosity),
> why is the channel swap clearly only itermittent ...? :-O]

I don't know for sure yet but I can speculate:

Normally PCM audio flows in three signals:

data
bit clock
sample clock

When starting to send/receive data, you need to sync up your data bits
to line up within a cycle of the sample clock, and you need to do it on
the correct edge of the sample clock.

It looks like this synchronization is not happening correctly for the
s/pdif encoding. Clearly, the data flow up to that point is working
correctly, because this problem doesn't happen on the analog outs. Also
it is apparently not a hardware problem because it works fine in mp3
mode.

So it looks like some step in the initialization is not happening
correctly and that's what I'm looking at right now. This would be
consistent with the intermittency we're seeing. It is also possibly
related to the slower frequency stabilization that is observed when
switching mp3->pcm vs pcm->mp3.

Sean