Bugzilla – Bug 9904
Mp3 silence results in "loss of Lock" for external dac via COAX
Last modified: 2009-10-22 11:15:40 UTC
Hello, I really hope you can help me! I have quite a few MP3 audio files which include moments of total silence (such as BBC Podcasts, end of music tracks). When these files are played via Digital out (SPDIF COAX) into a BEL CANTO DAC3 I get a very loud POP through the speakers whenever there is a moment of total silence, and the display on the BEL CANTO indicates a moment where the digital signal lock is lost. So basically, this means there is no digital signal being sent from the "Squeezebox Receiver" during moments of silence in MP3 files. I have tried converting an original MP3 file with these issues into FLAC and when playing this file the problem doesn't occur. Some external DACs won't POP loudly when there is a momentary loss of signal, but there are many DACs that do. So when testing for this issue you may need a DAC that has a "Digital Lock" indicator light of some sort rather than listening for a POP. I have this problem in many MP3 files, but an example mp3 file for you to try can be found in the latest episode of "In Our Time" at around 20 seconds before the end, in between the end of show and the BBC advert. I suggest that a course of action would be to update the firmware so that whenever there is total silence in an MP3 it is treated in the same manner as when silence is encountered in FLAC. This POP is so loud on my system its actually damaged my speakers and they've gone in for repair. I'm using FLAC only for now. I'm don't want to use TosLink as I've tried it and it sounds "thinner". If FLAC works with silence then MP3s should too. Help! I can help you resolve this in any way. Thanks
Just tried this again with the nightly build (firmware 53) and its still losses digital lock in moments of mp3 silence. I'm hoping this is an easy problem to solve with the MAD firmware. Help!
Created attachment 4212 [details] Clip of MP3 file with brief moment of silence in between items that causes loss of digital lock. I've attached a mp3 that contains an example section of mp3 silence (from a standard BBC Podcast) that causes momentary loss of digital lock on an external dac via spdif. The moment occurs at the end of the program and before the BBC promo. I have many music files that exhibit the same problem though. If you try converting this mp3 file to FLAC and play it though the digital lock remains steady. My suggestion id that the firmware for MP3 playback is changed so that it behaves in the same way that the FLAC routine does when it encounters zero noise within a file. This mp3 file was split for testing purposes, but the error is in the original file in the same spot. Thanks to all who can help!
During MP3 output, there is a continuous SPDIF signal which a DAC should have no problem locking to. Is there some kind of silence-detection built into your DAC that powers down during silence or something? Sean do you have any other ideas what might be causing this?
Colin, SB3 maintains s/pdif signalling during periods of silence. There are only two possibilities here: 1. Your DAC has a bug which causes it to not handle digital silence correctly. 2. You have a cabling or electrical problem. Digital silence over S/PDIF is electrically a somewhat special case which can reveal interface issues. To troubleshoot, first try TOSLINK (optical). If you still get the pops then the problem is not with connectivity, but with how your DAC handles the data. If you do NOT get the pops when using TOSLINK, then you should try a different coax cable. Try a decent 75 ohm video cable.
(In reply to comment #3) > During MP3 output, there is a continuous SPDIF signal which a DAC should have > no problem locking to. Is there some kind of silence-detection built into your > DAC that powers down during silence or something? > > Sean do you have any other ideas what might be causing this? > Thanks for giving me some help on this issue. Much appreciated :) I don't think there is any silence-detection, but I'll call the manufacturer. However, if it did would it not lose lock with the same file once it was converted to FLAC? It doesn't lose lock with a FLAC conversion of the same file.
> It doesn't lose lock with a FLAC conversion of the same file. Hmm, that's surprising... it raises more questions than answers actually. Please do the cabling tests first, and we'll go from there. The TOSLINK test in particular will be most helpful to understand whether we have a data issue or a connectivity issue. Also, is there any lock _indicator_ on your DAC, or are you going only by the popping sounds? There are other things that can cause pops, eg corrupted mp3 files, a bug in the decoder, etc. If it's an MP3 issue then you should hear the same thing from SB3's analog outputs.
Created attachment 4226 [details] Tones and silence for testing brief loss of lock on external DAC This is a file I've created that highlights the loss of digital lock on external DACs via SPDIF or TOSLINK. The same file once converted to other formats such as FLAC, Ogg or WAV doesn't produce the same error. When testing do so a few times please and only check via a reliable loss of lock indicator on the DAC. Thanks :)
Many thanks for the help on this and going to the trouble of testing the file. AS a bit of background, my rig is made up of high-end BEL CANTO monoamps and DAC3, with top-end JPS Superconductor 2 coax cables, with power conditioning. I've just tried the TOSLink cable and the loss of lock indicator light still goes off. Any ideas why a FLAC, OGG, WAV version of the SAME file never produce the same loss of lock as I get with the MP3 version? I'm not going by the pop sounds - only the loss of lock light. I don't think that testing the SBR via the audio outs would help us detect a momentary loss of digital signal would it? If its alright, could you try the NEW file I've created (with tones and silence) a few times and please only check the digital lock indicator on your DAC. Thanks very, very, very much Sean for the help :)
QA to reproduce
Changing target to next release
Investigating
Thanks James. If you'd like a short film of the issue occurring with my BEL CANTO DAC3 please let me know.