[Morsego]

Hi,

Before posting here, I did extensive tests and all lead to the same result so I now assume there's a bug in the MP3 audio rendering in XBMC specifically on output volume.

My environment :

- HTPC with OpenELEC 3.2 - Audio out with HDMI connected to a high end receiver and then to a flat TV screen
- Desktop with Ubuntu 13.10 Saucy Salamander - Audio (pulseaudio) out with analog jack connected to a high end stereo amplifier

- XBMC OpenELEC : Frodo 12.2 + GIT commits
- XBMC Desktop : 12.2 stable from Nathan Rennie-Waldock PPA and 12.3~git20131213.0944 from “XBMC for Linux” team

- XBMC Settings : No replain gain anywhere (not within audio tags nor within XMBC itself)

Short description : MP3 files sound much lower in volume than any other tested format

Long description :
I was testing some new songs (OGG) on my living room with my HTPC and I immediately noticed they sounded "very loud" compared to all my usual music collection (fully in MP3 VBR 320). I came back to my desktop to make a quick test and it turned out that these songs sounded as loud as my other files in the music collection, give or take.

I pushed further the tests. I took 2 songs which sound loud right from the begining and I decoded the OGG files back to WAV and re-encoded them in WAVPACK, FLAC and MP3 in 3 flavours : 1/ Custom script using GStreamer 2/ lame -b 320 -h and 3/ same as "2/" but with --noreplaygain in case there could be any difference.

All 7 files (OGG, WAV, WAVPACK, FLAC, MP3 in 3 flavours) sounded exactly the same on my desktop in various players (DeadBeef, VLC, Clementine, MPlayer)

On my HTPC, in XMBC, there was a difference : WAVPACK, FLAC and OGG sounded all the same and all the MP3 variants sounded quite lower than the other formats (they sound exactly the same between all variants)

Ok, back to the desktop. Install XBMC 12.2 from Nathan's PPA, redo the same tests => Same results. Replace XMBC with the XBMC Team version, redo the same tests => Same results.

So, unless there's something pretty messed up here, I narrowed the problem to the MP3 decoding engine in XBMC which, for some reason, produces an output volume for MP3 files considerably lower than any other format I tested!

Can some XMBC developper take a look and confirm the issue ?

[scott967]

Not a dev, but I am unable to replicate your results. I tested on XBMC 13 20140214 nightly on Win 7 using realtek high def audio driver. I obtained a 60 sec pink noise sample recorded at 44.1k and created wav and mp3 files in Audacity (for mp3 audacity uses lame encoder at VBR). I then played these back in XBMC set to WASAPI through the computer speakers and recorded in audacity using the "stereo mix" recording input at 48k sampling rate. I analyzed the recorded samples using the audacity spectrum analyzer and found the wav and mp3 files had identical results, except the mp3 sample fell off more sharply above 20k. That may be an artifact of resampling from 44.1 to 48k, don't know but I'm not too concerned about output at those freqs.

scott s.
.

[jjd-uk]

The difference is you tested with a Gotham build while original poster was testing with Frodo.

Morsego, no further work development work is being done with Frodo and for Gotham we have a new audio core. We are getting really near to beta for Gotham now so all testing for bugs should be done with a Gotham v13 nightly build as we will only fix bugs found in these builds.

[scott967]

You're right. Went back to my 12.2 test bed and see MP3 playback is off several dB.



scott s.
.

[jmarshall]

Nice testing!

[Morsego]

Hi,

scott967: you're right too! I've quickly tested 13.0~git20140104.0734-alpha11 from “XBMC for Linux” team and I couldn't find any audible difference between all 6 test formats I have (repeated through 7 different songs so 42 test files in total). I'm glad the issue does not exist in Gotham.

I also tested output volume between Frodo and Gotham to see if Gotham's output volume was "Frodo MP3 output volume" (low) or "Frodo other-formats output volume" (normal?) and, fortunately, it's as loud as it can be!

And I also found out a new bug which, this time, affects both Frodo and Gotham : WAVPACK fileformat! All my test files start music right from the begining with quite loud sound and no slow intro fades like usual (this was the whole point of testing output volume ). All formats work perfectly except WAVPACK where the few first milliseconds get "swallowed" (or cropped). There's a very small but noticeable cut right at the begining of any song in WV format.

Maybe I'll make another post about that but I don't know how popular WAVPACK is in XBMC's users base. Well, all bugs should be squeezed in a perfect world

[jjd-uk]

If you confirm an issue with WAVPACK please post it on the bugtracker (link right at the top in the forums permanently displayed bar).

Normally we would ask for all potential bugs to be confirmed via the forum 1st before being reported by the bugtracker, however we're getting very near to beta for Gotham now so need to get things moving quickly if we're to get bugs fixed for Gotham.

If reporting an issue on the bugtracker there are several things you MUST do:

1. Describe the issue in as much detail as possible and the steps needed to take to replicate, imagine describing it to a child so never assume knowledge as it's far better to have too much information than too little.
2. A debug log file taken while you are replicating the issue.
3. For a playback issue like this a file that can be used to replicate the issue uploaded to somewhere like Dropbox, Skydrive (Onedrive), Google Drive or similar where no user account is needed to download.
4. A screenshot showing all your audio settings.