psaffrey
Posts: 4
Joined: Mon Oct 08, 2012 8:09 pm

Distorted sound

Postby psaffrey » Wed Feb 06, 2013 9:29 pm

I posted about this in General:

viewtopic.php?f=63&t=32061&p=276172#p276172

But I've tried a few more things now and I'm hoping somebody else might have solved the same problem.

Basically, sound is distorted playing through the 3.5mm audio jack, particularly at low volumes. The sound is like this with a clean Raspbian installation (2012-12-16). I'm using amixer to turn down the volume (sudo amixer set PCM -- -5000) and aplay on some of the preinstalled wav files in /usr/share/scratch/Media/Sounds/. I've also tried doing "sudo amixer cset numid=3 1" to no effect.

I have been using the RPi to play through external speakers with mpd, but the distortion is less obvious with software volume turned up to 100%, so I can't tell whether this problem has always been there and I didn't notice or is new. I have moved the RPi around a few times plugged into speakers and I wondered if I damaged it.

I'm going to try buying an external USB sound card to see if this addresses the problem. Any other suggestions?
drgeoff
Posts: 6961
Joined: Wed Jan 25, 2012 6:39 pm

Re: Distorted sound

Postby drgeoff » Wed Feb 06, 2013 9:57 pm

The audio from the 3.5 mm jack comes from DACs which are only 11 bit. So if the level is low, quantising distortion may be quite apparent.

If you want high quality audio you need to either derive it from the HDMI output or use a USB sound card. Both options have been widely discussed on these forums.
dom
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 5087
Joined: Wed Aug 17, 2011 7:41 pm
Location: Cambridge

Re: Distorted sound

Postby dom » Wed Feb 06, 2013 11:02 pm

With 11-bit audio you don't want to turn the volume down or you'll end up with something like 5 bit audio.
hasso
Posts: 1
Joined: Tue Feb 26, 2013 9:47 pm

Re: Distorted sound

Postby hasso » Tue Feb 26, 2013 9:53 pm

Same problem as described. Low volume sounds distorted and seems to have some slight background noise. This is using the analog jack with mpd, pulseaudio on ArchLinux. Turning up the volume to about 50% (mpc volume 50) or above makes the distortion less noticeable. I'd expect that a USB sound card would resolve this.
ski522
Posts: 394
Joined: Sun Sep 30, 2012 2:22 pm

Re: Distorted sound

Postby ski522 » Tue Feb 26, 2013 10:29 pm

hasso wrote: I'd expect that a USB sound card would resolve this.


Yes...many have been using this card with excellent results
http://www.aliexpress.com/store/product ... 55749.html
Image