runeUI shows wrong bit depth

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runeUI shows wrong bit depth

Postby Midnight » 05 Mar 2014, 10:01

Hi,

while playing a file my runeUI always shows "24 bit" instead of the actual bit depth "16 bit". See the attached screenshot.
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Last edited by Midnight on 05 Mar 2014, 14:51, edited 2 times in total.
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Re: runeUI shows wrong bitrate

Postby ACX » 05 Mar 2014, 12:52

It's MPD that sends that inaccurate info to the RuneUI, when listening to some MP3 (it never happens with FLAC, at least in my experience). You can try it by yourself, connecting to your device via Telnet on the MPS's 6600 port and sending a "status" command. Among the displayed info you will see something like:

Code: Select all
audio: 44100:24:2

when it should be audio: 44100:16:2.

It was also discussed here.
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Re: runeUI shows wrong bitrate

Postby Midnight » 05 Mar 2014, 13:17

Indeed. My mpd on my PC shows the same.

But some more problems:
When playing an Ogg Vorbis file runeUI shows "Stereo, f bit, 44.1 kHz, 0 kbps", while status shows:
Code: Select all
bitrate: 170
audio: 44100:f:2

The bitrate is constantly changing.

Only flac gives reasonable output: "Stereo, 16 bit, 44.1 kHz, 1046 kbps". But I wonder if this is the average bitrate or just the initial bitrate? Because status shows a constantly changing bitrate, too.
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Re: runeUI shows wrong bitrate

Postby ACX » 05 Mar 2014, 13:23

Take a look at the other thread I linked above :)
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Re: runeUI shows wrong bit depth

Postby Midnight » 05 Mar 2014, 15:32

Regarding the bit depth issue:
Lossy formats like MP3 or Ogg Vorbis aren't using pulse code modulation (https://en.wikipedia.org/wiki/Pulse-code_modulation) anymore, so there is nothing like a 16 bit or 24 bit MP3. Or to quote Wikipedia:
Bit depth is only meaningful in reference to a PCM digital signal. Non-PCM formats, such as lossy compression formats like MP3, AAC and Vorbis, do not have associated bit depths. For example, in MP3, quantization is performed on PCM samples that have been transformed into the frequency domain.
(https://en.wikipedia.org/wiki/Audio_bit_depth)

So these values are actually meaningless for the input. The decoder just recreates a PCM signal with a specific bit depth that can be send to the DAC.

And this is why there appears 24 bit for MP3s:
The libmad library returns 28 bit samples, mpd discards 4 of them and uses the remaining 24 bit. The mpg123 and ffmpeg libraries both return just 16 bit samples.

So IMHO the bit depth should be shown for lossless formats only.
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Re: runeUI shows wrong bit depth

Postby ACX » 05 Mar 2014, 15:38

That's interesting, I'll take a look and see if I can put such a conditional in that display section.
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