Hi, An annoying bug today: I imported a file using a drop box, and found that the result had some nasty crackling distortion in loud parts of the recording. On further inspection, the original MP3 opened in Audacity looks like this:
http://cs448.user.srcf.net/clipbefore.png So we can see there's some clipping due to poor recording technique, but the flat tops don't sound too bad on the recording, just introduces a little buzz. However, the imported WAV file looks like this: http://cs448.user.srcf.net/clipafter.png So we can see that there has clearly been integer overflow turning some of the very-nearly-max samples into very-nearly-min samples, and turning the flat top into a very high frequency saw wave. This sounds awful. So: the question is, where is this introduced. I reimported the file using rdimport and it apparently inherited a normalization value from the "ripper level" setting, default -13dBFS. This did not suffer the problem, showing flat tops appropriately squashed. As the import web service's workflow is to decode to WAV-signed-32, process, then encode (in this case, just reduce depth to WAV-16), this suggests the problem is introduced either during the processing stage or the encode. My suspicion was on the normalizer failing to notice an overflow, as the dropbox is configured to use -1dBFS normalization. However I suspect that's a red herring, as ps shows I am running rdimport --persistent-dropbox-id=12 --drop-box --log-mode --normalization-level=0 --autotrim-level=0 --delete-source --startdate-offset=0 --enddate-offset=0 Recordings /music/playout-dropbox/recordings/* Which looks to me as though a different bug has disabled normalization! Unless perhaps it ignores the norm-level=0 and gets that setting from elsewhere? Anyway I will continue to investigate; has anyone seen this before? Any hints on where to look next? The trickiest bit at the moment is that the web services code is hard to harness and test... Chris _______________________________________________ Rivendell-dev mailing list [email protected] http://lists.rivendellaudio.org/mailman/listinfo/rivendell-dev
