Re: [ARMini-support] Pops from the speaker
- From: Jim Lesurf <jcgl@xxxxxxxxxxxxxxx>
- To: <armini-support@xxxxxxxxxxxxx>
- Date: Fri, 26 Feb 2016 09:38:57 +0000 (GMT)
In article <55579c3cbbchris.lists@xxxxxxxxxxxx>, Chris Bell (Lists)
<chris.lists@xxxxxxxxxxxx> wrote:
I've only just started using the audio out (ARMiniX, bottom 3.5mm
socket) to play FLACs with !DigitalCd and I'm getting random clicks
and pops (even with no music playing).
Was a cause/solution found?
From experience with audio systems, the pops reminded me of poor earth
connections, so I checked all my external connections and even
disconnected anything that could cause an earth loop. I concluded the
cause wasn't external.
Pops are delivered via the audio output jack, are random and seem to be
triggered by USB activity (eg printing). Reports confirm that they
happen on Beagleboards as well as Pandaboards but are not, thankfully,
as common since the OS 5.22 upgrade. Someone at last year's SW Show
said he 'just has to live with them'.
I've not used my ARMiniX for a while, but I did get 'pops' with that when
using a test version of !DigitalCD to play Audio CDs in the optical drive.
However, I *didn't* get 'pops' problems with playing wave files. (I didn't
use flac much on the ARMiniX.)
They also occur when I used the currently released USB Audio modules and
tried to play files at rates above 44.k1 on my ARMX6.
In general they are a sign of buffer underruns. i.e. The audio isn't being
transferred via the buffers quickly enough. So you get bursts of silence or
sections of of the 'last buffer content' being repeated instead of the next
part of the music.
One problem here is many USB hubs, hosts, etc, tend to have odd quirks
which may need to be patched over by tweaks to the relevant software to
prevent this. This is obviously a PITA for firmware/OS/app developers in
these areas. AIUI this is what has been 'in the way' of USB Audio on the
ARMX6.
Audio is utterly intolerant of any problems of this kind as it is like
comedy where... timing is.... vital. 8-]
Whereas if you're transferring something like a text file it just means the
process took very slightly longer, but still works OK.
So such problems may be obvious when you play (or record) audio, but pass
un-noticed in other uses.
You *may* find that setting a much bigger (or smaller!) buffer size avoids
or reduces pops. Have a look at your !DigitalCD settings and experiment to
find out. Also check that you're playing using the option to use 'x2 rate',
with interpolation ticked. If the system is trying to do awkward rate
conversions that could make the difference between it being able to keep
up, or fail. (You can check the rate whilst playing by using !SoundCheck.)
All that said, the bottleneck may be further down the path out of user
control, so requires a tweak at a lower level.
Jim
--
Electronics
http://www.st-and.ac.uk/~www_pa/Scots_Guide/intro/electron.htm
Audio Misc
http://www.audiomisc.co.uk/index.html
Armstrong Audio
http://www.audiomisc.co.uk/Armstrong/armstrong.html
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