View Full Version : FLAC crackle

2007-06-02, 19:17
I have a FLAC file that plays fine on my laptop but on on my very new Squeezebox it has occasional crackling sounds, sort of like static or vinyl record crackling. I think it may be the high-frequency content. Because it sounds fine played on my laptop I think the problem lies in the Slimsever or Squeezebox.

I've searched the forums and have turned off the replay gain but it has no effect. Converting the FLAC to a WAV did not reduce the crackling. The crackling was almost gone when I converted to a variable bitrate MP3 (about 256 average), but I think that was because the highs were attenuated. I also reduced the volume from the Squeezebox to 50% but it didn't help very much. The crackling always occurs in the same places, not with high overall volume but the spectrum analyzer shows lots of high frequency content.

I'm running SlimServer Version: 6.5.2 - 12047 - Debian - EN - utf8 under Ubuntu (Xubuntu) on a 1 Ghz AMD laptop with 256 MB RAM.

Any thoughts? I bought the Squeezebox to replace a Roku and apart from this serious problem have been happy with the change.

2007-06-03, 00:15
So, if you convert the file from FLAC to WAV you still get the same crackling when played on your SB? Well, that eliminates any possible bug in the SB's FLAC decoder, and in turn suggests that the problem is in the FLAC file itself.

When you say it sounds fine when you play it on your latop - how are you playing it?

Also, how did you rip the file, and did the ripper report any errors? I've had instances when bad discs - especially the last track on an overlong compilation album - have given crackly rips, but EAC has always at least told me that it was having problems when it was ripping.

I'd try re-ripping if I were you.


2007-06-03, 12:04
I've done some more tests and am now convinced there is a problem with the Slim hardware or software. The rip was reported with no errors and the file sounds fine under various other playback methods.

At first I tested the FLAC on a newer IBM laptop with foobar and connected directly to headphones (reported above). No crackle.

Then I played the same file on my desktop connected to a nice outboard DAC (an Alien DAC) and then to powered monitors. No crackle.

Next I re-confirmed that the Slim setup described above produced the static/crackle on my home receiver and speakers, always at the same places.

Finally I connected the powered monitors directly to the Squeezebox and heard the same crackle in the same places, with the Squeezebox volume as low as 50.

If someone has a place to host the file (about 23 megabytes) I will be glad to share it for testing. I think I've ruled out any other source of the problem other than the Squeezebox or Slimserver.

2007-06-03, 12:37
On the chance that my server was underpowered, I tried running slimserver under Windows XP on a more modern machine. The crackle persists.

2007-06-03, 12:44
Have you tried playing the file with filetype "Flac built-in" unchecked.

2007-06-03, 14:26
If you're sure the file plays normally on a PC but not on a SB, please file a bug report, and you can upload the file as an attachment to the bug. http://bugs.slimdevices.com/enter_bug.cgi?product=Squeezebox2%2Fv3

2007-06-03, 14:34
Have you tried playing the file with filetype "Flac built-in" unchecked.

That didn't help. Forcing the FLAC to play as an MP3 helped (flac/LAME), but I wonder if it sounded a little muffled.

2007-06-03, 14:39
If the file sounded the same (i.e. the same crackle) with "built-un" unchecked - then it means there is somehting in the file as decoding will be done on the PC by the "flac" app and not on the SB3.

Either way - follow Andy's advice and see if support can hear the problem - it would help if you gave the elapsed time to the crackle.

2007-06-04, 16:47
If the file sounded the same (i.e. the same crackle) with "built-un" unchecked - then it means there is somehting in the file as decoding will be done on the PC by the "flac" app and not on the SB3.

I'm not so sure of this, as a WAV file also had the crackle but only on the slim system. I also looked at the original file in an audio editor and saw nothing that would produce the sound.

But in any event the problem is now gone, possibly from rebooting the server. That doesn't make a lot of sense since I heard the problem on a different server (unless the file was cached in the SB3?), but I'm at a loss as to the cause. Anyway, case closed as far as I'm concerned - I'd rather spend my time listening to music after all of this! Thanks all for your suggestions.

2007-06-05, 15:30
I've noticed this problem too, but as I only recently got my SB up and running I haven't had the chance to figure out where the problem lies. Some Flac files sound fine on PC, but crackle when played via SB.