Re: [Alsa-user] Higher quality dmix resampling

[Paolo S. <pms...@ya...>]

On Friday 15 May 2009, Grant wrote:

> > So how come that you don't get 'em with mpd?!
> 
> In mpd I specify oss instead of alsa.  If I specify alsa and involve
> dmix, I get static in mpd too.

you say OSS... but was that the "real" oss (does it still exist for
modern kernels/hardware?!) or was it just the ALSA oss emulation?

If it's the latter (as usually is on modern systems), then its just
the input interface that changes, you're goin' trough ALSA anyway.

On the other end, if it really was the former (real OSS stack), then 
likely you have a problem with mixed+conflicting drivers... ALSA and
"real" OSS can NOT coexist on a system.

> > again, I believe that your problem is completely unrelated to the
> > resampling algorithm used.
[...] 
> Well, there is a blog post under "A little hint for hda ALSA users" which says:
> 
> "if you own an hda-based soundcard and you head crackling sound while
> playing mp3s or similar, the problem is probably due to the bad
> samplerate conversion from 44100 to 48000."

Sorry, I won't believe that. AFAIK ALSA is a "layered" stack where 
higher level "functions" such as dmix and resampling are implemented
in their own layer which is "sitting on top" of the lover level ones
(such as hardware drivers). 
Obviously the higher level functions are not implemented within the 
hardware-specific low level drivers and -AFAIK- they remain the same 
whatever low level driver is in use. So how/why something like any 
given ALSA resampling algorithm could work differently when paired 
with different hardware?

BTW, on my HTPC (which by chance is the machine I'm on now) I have
an Intel DP35DP. That have an ICH9 HD Audio Controller. Which I use
when playing to the HDTV own speakers (rather than the HiFi system,
for which as said I use a Juli@).

Needless to say, it works perfectly with any resampling algorithm, 
using either analog or digital outputs at whatever sampling rate.

I also have an old laptop with ICH4, my office desktop which have 
ICH5, another laptop with ICH7, ... not counting the large number 
of other Linux machines I manage at work. I believe I can say to 
have seen quite some different hardware/software combinations. In 
some 10+ years of Linux system management I have had troubles with 
unsupported hardware, incomplete and/or broken drivers, etc, but 
have never experienced "static" noise or otherwise broken audio 
due to poor resampling using the default ALSA config.

On the other end, your referenced blog says explicitely:

> http://blog.flameeyes.eu/tag/alsa/page/2
> 
> "although I admit I haven’t tried it first hand, as I don’t have any hda-based soundcard beside the laptop"

who should I believe? my own experience or his 2nd hand 
rumors? ;-)

> > Only once you've got the default config to work properly you may start
> > experimenting with more sophisticated options.
> 
> That sounds good, but what else can I try?

what I'd do as a first step is trying to get your own
distribution / installation / customizations out of the
mix.

So get some proven Live CD/DVD (NOT Gentoo-based!) and 
try with those. I'd try with Ubuntu 9.04, then perhaps 
Mandriva 2009, good old Knoppix, etc. 

Try to get systems with several different kernel/alsa 
version combinations, and report what happen... maybe
it'll turn out that you'll have to file a bug report.


Ciao,
                                Paolo.

--
Skype: Paolo.Saggese
http://borex.lngs.infn.it/saggese
You can still escape from the GATES of hell: Use Linux!
-- 


Ciao,
                                Paolo.

--
Skype: Paolo.Saggese
http://borex.lngs.infn.it/saggese
You can still escape from the GATES of hell: Use Linux!