mplayer -ao pcm poor quality when at slow speed

chadwick · 03-01-2007, 11:09 PM

I would like to do a batch job to convert numerous audio files to slow speed.
It's for a language class. There are several files that need to be listened to, and it would be good if they could be listened to at slow speed. Since not everyone has a player that can do this, it would be good to just have the audio files available at different speeds.

I found that "mplayer -ao pcm" outputs a file called "audiodump.wav". That takes the usual flag -speed. For example "mplayer file.mp3 -ao pcm -speed 0.9" produces a file at 90 % of the regular speed.

If I listen to one of these files using mplayer (not dumping it using -ao pcm, i.e. just using "mplayer file.mp3") and slow the audio down to 80 % (using open square bracket "[" while the file is playing), then the quality is good. However, if I use -ao pcm as explained in the previous paragraph, and use -speed 0.8, then the quality of the sound is poor. It comes out with a metallic vibrating sound that is very unpleasant to listen to.

What's causing this? Is there a quality-adjusting flag that will fix this problem?

By the way, if I create audiodump.wav without the -speed flag and then listen to it at slow speed using mplayer, (with square bracket) then there is no problem.

Thanks.

SciYro · 03-02-2007, 12:29 AM

tested it on my machine, i cant see any difference.

Perhaps its your mplayer config file that has some different options?

chadwick · 03-03-2007, 03:53 PM

Okay thanks for checking. My config file ~/.mplayer/config is blank.
Maybe if I tried it with your config options it would work?

SciYro · 03-03-2007, 04:40 PM

Sorry, the only options that are active are font configuration options.

Code:

fontconfig=1
subfont-osd-scale=4
subfont-text-scale=3

are you sure you looked at all the options? Mplayer contains two config files, one in /usr/share/mplayer/mplayer.conf and the other local to the user in ~/.mplayer/config, both of which are used.

chadwick · 03-03-2007, 05:55 PM

I checked but the only thing in /usr/share/mplayer/ is the skins/ directory.

I did manage to stumble across a file called /etc/mplayer/mplayer.conf. That one is entirely commented out except for also a few lines about fonts.

Code:

fontconfig = yes
font = "Sans"
subfont-text-scale = 3

One of the things it says is

Code:

#
# MPlayer configuration file
#
# Configuration files are read system-wide from /usr/local/etc/mplayer.conf
# and per user from ~/.mplayer/config, where per-user settings override
# system-wide settings, all of which are overrriden by the command line.
#

so, at least according to that, ~/.mplayer/config is the relevant config file.

Oh well, thanks again. Maybe I'll look again through the different runtime options that can be passed.

SciYro · 03-03-2007, 09:57 PM

strange... owell, perhaps try another way to recode the sound, sox with the "rate" option perhaps?

chadwick · 03-04-2007, 03:18 AM

I'd actually never heard of Sox, but it looks interesting. According to http://sox.sourceforge.net/, you can change the speed without changing the pitch which might end up being a nice bonus. I think I'll give that a shot but might have to put it on the backburner for a week or so.