MP3 playback artifacts with PWD MKII


#1

I’ve got a currently updated PWD MKII (v2.20) with bridge (v2.14b). Being one of the first times I played MP3 through it from the bridge interface, I noticed a strange warbling sound artifact. I heard it on many different MP3s from different places. It is noticeable as a constant warbling or swarm of mosquitos type sound at a low level, which is very apparent when playing music that is low in volume (requiring raising the volume knob) or has quieter parts. It seems to affect any MP3 file, while all my flac files play back perfectly ok.



Does anyone else notice this? It seems like a decoding artifact, my Saturn had the same problem with many MP3 files, but they were perfectly fine played back on a computer. Seems like the bridge software suffers from a similar problem. If this is a known bug or an actual bug that affects everyone’s bridge, I’d say it would be nice to fix. Normally I would not listen to MP3 but some circumstances required me to use some MP3s and this artifact makes the PWD not a good solution if there are MP3s in the playlist.


#2

Not a known issue or bug as far as I know. To my knowledge you are the first to report this behavior. That does not mean that it is not a bug in the Bridge, only an issue that has not been previously identified. I would guess that few people do any serious listening to lossy formats such as MP3.



I would suggest finding lossless copies of your MP3 tracks. Barring that, I would convert them to FLAC or some other format that does not exhibit any such playback anomalies. Certainly I would keep original copies of the MP3s as well, just not in the media library used by the PWD. If you do transcode the MP3 tracks they need to be clearly tagged and named as coming from MP3 source so that at some time in the future you are not left wondering why some of your tracks seem to be of lower quality.



J.P.


#3

I think it would be better for this problem to be fixed rather than deal with that kind of file management nightmare. Supposedly 320kbps MP3 should be quite transparent for most cases. Unfortunately this artifact makes it obvious which file is from MP3. I’m surprised no one else has ever seen this issue after the bridge being available for so long now. Unless this is only a problem with 2.14b and everyone is still using 2.13c =)


#4

Easy enough to try and see if another firmware version works differently. You can load any firmware version you like. Any firmware will work on any Bridge.



Suggested versions to try are 0.2.8, 0.2.12 and 0.2.13c. Those seem to be the ones reported to be the best sounding.



J.P.


#5

Tried 2.13c but unfortunately the problem is there as well.


#6

How about if you connect your computer via USB in the PWD instead of the Bridge? Is there still a problem? You first need to identify and isolate the source of the problem and it might be the Bridge, the PWD, your mp3 files, the filter you are using, etc.


#7
How about if you connect your computer via USB in the PWD instead of the Bridge? Is there still a problem? You first need to identify and isolate the source of the problem and it might be the Bridge, the PWD, your mp3 files, the filter you are using, etc.


That won't work, because every other interface on the PWD is uncompressed digital audio. The computer would have converted it to PCM if sourced from an MP3, and that is done correctly without the same artifacts. Only the bridge takes a raw MP3 file/stream and decodes/playbacks them natively. If anything is wrong, it has to be the decoding layer of the software.

My bridge is able to send perfectly good sounding digital audio over to the PWD when PCM, WAV or FLAC format. So the hardware works fine. But sending MP3, I assume it doesn't break the fact that it still sends bit correct information from the bridge to the DAC, but the MP3 decoder has a problem or is of poor quality in that conversion to an I2s audio stream. It definitely sounds like a software issue.