Emphasis bit

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Joined: Thu May 05, 2011 9:36 am

Emphasis bit

Post by Reuti » Thu May 05, 2011 1:22 pm

Both, the mp3 and flac file format, have a bit to indicate emphasis. I.e. for files which would need de-emphasis during playback. I found neither Decibel, nor VLC or iTunes honoring this bit - is this correct? I created files with lame where you can set the bit with -e from a test CD from Denon where you can clearly see its increasing amplitude for a higher frequence for a signal that should be constant. The CD is so old, that it has the emphasis bit is only set in the sub-channel data, not the TOC. So iTunes and also Max are failing to detect the emphasis and are ripping it unaltered. So for curiosity I made an mp3 out of it and set the bit with lame (and it's only setting the bit without altering the signal). The bit is set as I can check with a hex editor. *)

Honoring would in fact mean to either: tell the S/PDIF output to set the bit in the data stream and let the DAC handle it, or do a software de-emphasis before the analog output is delivering the data to the amplifier.

If no player is honoring the bit, it would be good to be removed from the specification as it creates confusion when you would trust it. And to clearly state: apply de-emphasis beforehand in software by sox or other means to your files.

*) The reason behind are the many classic CDs (also from Denon) I own where I can see the external DAC lighting up emphasis in its display during playback.

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