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Thread: Pre-emphasized CDs

  1. #1

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    Pre-emphasized CDs

    I think dBpoweramp is the best CD ripper and conversion utility out there. The reference edition with the multi-CPU support is a great time saver when ripping large libraries of CD's. Thanks for the excellent program.

    One question - Some CD's have the upper frequency range emphasized. CD players typically will recognize this and during the DA process de-emphasize so the response on playback is flat. The information on whether the track is emphasized is on the CD and transports detect this and act accordingly.

    With audio moving more and more to computer based and to alternative encoding formats ( I use FLAC) this information is lost and these CD's sound shrill when played.

    As far as I can see dBpoweramp does not recognize this nor have the option to perform de-emphasis when ripping and transcoding.

    Is there a way around this?

    Are there plans to include such capability in the program. This would be a big draw for the digital audiophile community.

  2. #2
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    Re: Pre-emphasized CDs

    Pre-emp is not supported, the discs are very rare as far as I can tell.

  3. #3
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    Re: Pre-emphasized CDs

    In "The Compact Disc Handbook" (Ken C. Pohlmann; A-R Editions Inc.ISBN 0-89579-300-8) the author gives a very clear explanation of how emphasis is applied, and the frequencies affected. The indicator signal to "tell" the CD player whether or not to apply de-emphasis is contained in the Q Channel.
    I agree with Spoon that emphasis is pretty rare in recent CDs, but may occurin older ones. The important point (to me, anyway) is that the CD player applies de-emphasis if it is required, in response to the Q Channel signal, so it should certainly not affect audio ripped from a disc. Question? Do CD-DVD ROMs and 'burners' respond to the Q Channel signal - that would be the crux of the matter. Tony

  4. #4

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    Re: Pre-emphasized CDs

    This could be done using a DSP effect.

    Is there an API for 3rd party developers?

  5. #5
    dBpoweramp Guru LtData's Avatar
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    Re: Pre-emphasized CDs

    No, but you can utilize DirectX or VST plugins as a DSP effect in dMC.

  6. #6
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    Re: Pre-emphasized CDs

    The DSP effects are non-trivial to implement, how easy is pre-emp to implement?

  7. #7

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    Re: Pre-emphasized CDs

    De-Emphasizing is (normally) done using a passive network with a 50/15 us time constant.

    This would have to bew implemented a IIR filter, as I have read elswhere a first order filter would get closer than 0.1 dB.

    But I would have to look for the coeffs first...


    ciao, TommyZ

  8. #8

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    Re: Pre-emphasized CDs

    This is a 101 coeff FIR filter that emulates the needed deemphasis.
    Note that it is NOT symmetrical, as it also emulated the phase (although only to about 10 degrees). But the amplitude is within 0.1 dB up to 20 kHz
    Where do I find info on implementing DirectX or VST plugins ?

    101
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  9. #9
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    Re: Pre-emphasized CDs

    On what (lossless) file formats is a pre-emphasis tag/comment frequent enough to be interpreted during playback?

  10. #10
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    Re: Pre-emphasized CDs

    Pre-emph details never make it from the cd ripper to audio format.

    --

    Tommyz: sorry I did not see your post above, which language do you work in? c++

  11. #11

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    Question Re: Pre-emphasized CDs

    Track Technical is reporting that all of the tracks on the Japanese band Casiopea's 'Mint Jams' CD have pre-emphasis. None of their later discs seem to have it, so this might well be the only CD in my collection which is affected.

    Are there any plans to implement a de-emphasis DSP?

  12. #12
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    Re: Pre-emphasized CDs

    Only if opportunity presents its self.

  13. #13

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    Re: Pre-emphasized CDs

    Does this constitute an opportunity?

    http://www.picosound.de/E_soft.htm*emphasis

  14. #14
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    Re: Pre-emphasized CDs

    That has been around 5 years, has no source code, no visible license and no way of controlling externally, so no.

  15. #15
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    Re: Pre-emphasized CDs

    sox is GPL'ed and includes a de-emphasis filter. You don't even need to redistribute it if your "DSP" is merely a command line invoking sox, with a "please download and install sox version xxx" error message if it does not find it.

    And, I'd still want a Vorbis comment saying PRE-EMPH: [Yes/Corrected/No]


    sox: http://sourceforge.net/project/showf...group_id=10706

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