rme 9632 crackling when sound > 0db

rme 9632 crackling when sound > 0db

[Ed Wildgoose]

Hi, I'm running kernel 2.6.5-mm1 with built-in alsa drivers.  Also, v 
1.04 of the various alsa utils, etc.

I'm playing (for example) Dido - No Angel, track "Isobel", and according 
to the hdspmixer tool, at the end of the track the drums have transients 
that go greater than 0db, and this causes nasty metallic crackles on my 
RME 9632 (tested with both Alsa and OSS interfaces).  Without looking at 
the code, I'm wondering if there is an overflow occuring, ie something 
unsigned going into a signed value and causing this...  However, it 
doesn't seem that likely, for example if you turn up the middle layer of 
mixer controls and then turn down the last layer of output mixer 
controls then as long as the red clip light isn't on then everything is 
still ok, ie the crackle isn't occuring as a result of the first layer 
of software mixing, it purely seems to be something happening *after* 
the last mixer control

You can also simulate this simply by turning up the mixer controls so 
that normal music starts to clip.  Same effect.

Two points to note, first I don't remember getting this on an alsa 
snapshot from about 1-2 months ago, so I'm thinking it's a driver issue, 
rather than a feature of this card?  Secondly, before now I couldn't use 
the card at all with many apps, I would just get constant over-runs and 
other problems.  So thankyou for fixing those problems!

Just a heads up, this card still doesn't work with mplayer 1.0 pre3.  
The sound appears to be playing too slowly, and several times a second 
there are "xruns" reported (which makes sense).  I will try and rip out 
the mplayer audio code and make up a test app so that I can experiment 
further with this. 

Thanks to everyone who has made Alsa what it is today!

Ed W


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Re: rme 9632 crackling when sound > 0db

[Ed Wildgoose]

>
> You can also simulate this simply by turning up the mixer controls so 
> that normal music starts to clip.  Same effect.



At risk of creating noise.  Further experimentation shows that you need 
to set the output levels to +4db in hdspconf for this crackling to 
occur.  So in fairness this could really be an overdriven output...?

The -10dbv output level is significantly quieter than any other 
equipment that I own (I know it's what they call consumer output device 
level, but still...)

Ed W


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Re: rme 9632 crackling when sound > 0db

[Joachim Deguara]

The good news: you don't have a driver problem!  But it sounds like you 
have a Wordclock problem.  Namely, your rme 9632 has a different clock 
than your playback device (D/A) and they are not in Sync.  Check the 
setting for who is (and should be) Wordclock Master and take adjust 
accordingly.  You can set the mode of synchronisation for you card by 
editing /etc/asound.state and the running "alsactl restore".

-joachim

Ed Wildgoose wrote:
> 
>>
>> You can also simulate this simply by turning up the mixer controls so 
>> that normal music starts to clip.  Same effect.
> 
> 
> 
> 
> At risk of creating noise.  Further experimentation shows that you need 
> to set the output levels to +4db in hdspconf for this crackling to 
> occur.  So in fairness this could really be an overdriven output...?
> 
> The -10dbv output level is significantly quieter than any other 
> equipment that I own (I know it's what they call consumer output device 
> level, but still...)
> 
> Ed W
> 
> 
> -------------------------------------------------------
> This SF.Net email is sponsored by: IBM Linux Tutorials
> Free Linux tutorial presented by Daniel Robbins, President and CEO of
> GenToo technologies. Learn everything from fundamentals to system
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> _______________________________________________
> Alsa-devel mailing list
> Alsa-devel@lists.sourceforge.net
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-- 
Joachim Deguara				Email: dga@idmt.fraunhofer.de
Fraunhofer IDMT, Langewiesener St. 22, 98693 Ilmenau, Germany
Phone: +49 3677/69-4851 		Fax:   +49 3677/69-4399


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Re: rme 9632 crackling when sound > 0db

[Ed Wildgoose]

Joachim Deguara wrote:

> The good news: you don't have a driver problem!  But it sounds like 
> you have a Wordclock problem.  Namely, your rme 9632 has a different 
> clock than your playback device (D/A) and they are not in Sync.  Check 
> the setting for who is (and should be) Wordclock Master and take 
> adjust accordingly.  You can set the mode of synchronisation for you 
> card by editing /etc/asound.state and the running "alsactl restore".


Hi, Thanks for the thought, but I don't see how this could be the 
issue?  I am reading input from the HD, writing it to the card via 
either oss or alsa, and the output is analogue to a pre-amp and then on 
to an amplifier.  The crackle only occurs when I use +4db as the output 
level, and then either find a song which clips anyway, or crank up the 
mixer so that the output clips.  It could actually be some sort of 
electrical issue at the pre-amp to be fair, it's just that I don't 
remember it happening before?  It doens't seem to be a problem if I drop 
the output level to the -10bdv setting for example.

The main thing I would prefer to debug right now anyway is why mplayer 
doesn't work with this card.  A cursory glance at the mplayer output 
code suggests that everything looks fine...  Oh well, will need to break 
out that code and study it a bit more - most other apps are working now 
though

Thanks

Ed W


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