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Reverse CD Pre-Emphasis

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ffmpeg -i input_file -af aemphasis=type=cd output_file

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This will apply de-emphasis to reverse the effects of CD pre-emphasis in the somewhat rare case of CDs that were created with this technology. Use this command to create more accurate listening copies of files that were ripped 'flat' (without any de-emphasis) where the original source utilized emphasis. For more information about CD pre-emphasis see the Hydrogen Audio page on this subject.

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ffmpeg
starts the command
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input_file
path, name and extension of the input file
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-af aemphasis=type=cd
activates the aemphasis filter and sets it to use CD equalization
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output_file
path and name of output file
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Check/Compensate for CD Emphasis

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While somewhat rare, certain CDs had 'emphasis' applied as a form of noise reduction. This seems to mostly affect early (1980s) era CDs and some CDs pressed in Japan. Emphasis is part of the Red Book standard and, if present, must be compensated for to ensure accurate playback. CDs that use emphasis contain flags on tracks that tell the CD player to de-emphasize the audio on playback. When ripping a CD with emphasis, it is important to take this into account and either apply de-emphasis while ripping, or if storing a 'flat' copy, create another de-emphasized listening copy.

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The following commands will output information about the presence of emphasis when run on a target CD:

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Cdda2wav: cdda2wav -J

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CD Paranoia: cdparanoia -Q

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In order to compensate for emphasis during ripping while using Cdda2wav, the -T flag can be added to the standard ripping command. For a recipe to compensate for a flat rip, see the section on de-emphasizing with FFmpeg. +

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