Help needed from MPEG audio experts

Discussion in 'rec.audio.pro' started by Gary, Sep 2, 2003.

  1. Gary

    Gary Guest

    I bought this little handheld multi-track recorder called the Korg
    PXR-4. It encodes audio to SmartMedia using MPEG-1 layer 2 or MP2.
    The MP2 files it creates load just fine into audio apps like Sound
    Forge. Unfortunately, if you attempt to transfer a file that
    originated elsewhere and was converted to MP2, or one that originated
    on the PXR-4 but was edited, it often will crash the unit with a
    DSP:0015 error (not that I expect anyone outside of the Korg design
    team to know what this really means).

    To attempt to see what will make the unit crash I've recorded a number
    of test files with sweeps at various levels, noise, speech, etc.
    Oddly most of these work fine, but when I take an actual music track
    say from SONAR, and covert it to the proper MP2 format, it will still
    crash the unit within 15 seconds.

    I got a copy of the ISO document that describes MP1, MP2, and MP3 and
    have written a program that will scan an MP2 file and read the headers
    (which is not very exciting, but easily enough done). I don't believe
    the compatibility has anything to do with the original or copyright
    bits because I've tried various permutations of that and it seems not
    to matter.

    I'm guessing that the h/w encoder in this unit is only able to do a
    subset of what a full-fledged encoder really needs to do, but since
    they've balanced it out with a matching decoder it doesn't matter so
    long as you stay on the unit.

    My question to you experts - what could it possibly be?
  2. SCMS? Don't know, but some material from other sources may have such a bit
    turned on while the original files from the Korg don't. There are too many
    possibilities. Perhaps import into another application as a test? If you
    check the headers there should always be a SCMS bit available, but if Korg
    doesn't implement it, perhaps the header gives the program the wrong
    information from where that bit would normally reside on. Certainly that
    should make an application go "what the fuck?". At least with the
    information you've provided it seems like a possibility, however unlikely.

    --


    Roger W. Norman
    SirMusic Studio
    Purchase your copy of the Fifth of RAP CD set at www.recaudiopro.net.
    See how far $20 really goes.




    "Gary" <faultline1989@yahoo.com> wrote in message
    news:87dac912.0309011721.32b5ed96@posting.google.com...
    > I bought this little handheld multi-track recorder called the Korg
    > PXR-4. It encodes audio to SmartMedia using MPEG-1 layer 2 or MP2.
    > The MP2 files it creates load just fine into audio apps like Sound
    > Forge. Unfortunately, if you attempt to transfer a file that
    > originated elsewhere and was converted to MP2, or one that originated
    > on the PXR-4 but was edited, it often will crash the unit with a
    > DSP:0015 error (not that I expect anyone outside of the Korg design
    > team to know what this really means).
    >
    > To attempt to see what will make the unit crash I've recorded a number
    > of test files with sweeps at various levels, noise, speech, etc.
    > Oddly most of these work fine, but when I take an actual music track
    > say from SONAR, and covert it to the proper MP2 format, it will still
    > crash the unit within 15 seconds.
    >
    > I got a copy of the ISO document that describes MP1, MP2, and MP3 and
    > have written a program that will scan an MP2 file and read the headers
    > (which is not very exciting, but easily enough done). I don't believe
    > the compatibility has anything to do with the original or copyright
    > bits because I've tried various permutations of that and it seems not
    > to matter.
    >
    > I'm guessing that the h/w encoder in this unit is only able to do a
    > subset of what a full-fledged encoder really needs to do, but since
    > they've balanced it out with a matching decoder it doesn't matter so
    > long as you stay on the unit.
    >
    > My question to you experts - what could it possibly be?
  3. nappy

    nappy Guest

    "Gary" <faultline1989@yahoo.com> wrote in message
    news:87dac912.0309011721.32b5ed96@posting.google.com...
    > I bought this little handheld multi-track recorder called the Korg
    > PXR-4. It encodes audio to SmartMedia using MPEG-1 layer 2 or MP2.
    > The MP2 files it creates load just fine into audio apps like Sound
    > Forge. Unfortunately, if you attempt to transfer a file that
    > originated elsewhere and was converted to MP2, or one that originated
    > on the PXR-4 but was edited, it often will crash the unit with a
    > DSP:0015 error (not that I expect anyone outside of the Korg design
    > team to know what this really means).


    What this probalby means is that the DSP decoder failed due to the units
    inability to correctly parse ANY MP2 or MP3 file format. While writing an
    MP3 class for a well known MI company I discovered that there are many
    little gotchas when trying to accomodate MPx files from different sources.
    Proper parsing of the file would fix that .. It appears the DSP section of
    the decoder is getting a bad block start because of incorrect parsing of the
    data MP3 headers. If it starts on bad data then anything can happen from
    there on in.

    nappy
  4. Gary

    Gary Guest

    "Roger W. Norman" <rnorman@starpower.net> wrote in message news:<bj2abm$t4n$1@bob.news.rcn.net>...
    > SCMS? Don't know, but some material from other sources may have such a bit
    > turned on while the original files from the Korg don't. There are too many
    > possibilities. Perhaps import into another application as a test? If you
    > check the headers there should always be a SCMS bit available, but if Korg
    > doesn't implement it, perhaps the header gives the program the wrong
    > information from where that bit would normally reside on. Certainly that
    > should make an application go "what the fuck?". At least with the
    > information you've provided it seems like a possibility, however unlikely.


    Hey Roger,

    Files created on the Korg have the Copyright and Original bits set to
    1 in the header of each frame.

    These files are easily read by Sound Forge (which doesn't write
    directly to MP2).

    WAV files created e.g. by Sound Forge and run through dBPowerAmp MP2
    convertor have both bits set to 0. However I have created files such
    as the sweep tones I mentioned which have both bits set to 0 and the
    Korg doesn't typically mind.

    I did create one file which was me doing a countdown, 10, 9, 8, 7,
    etc. then I peak normalized each word to the corresponding # of -dB.
    In my tests this would crash right after "3". So I did a test tone at
    -3 dB with a ramp up from 0 at the beginning and it too crashed the
    Korg. I concluded it was level sensitivity, only to be baffled when I
    created another suite of tones going up to 0 dB, and they all played
    fine.

    Having looked at before/after WAV to MP2 yes it is obvious that the
    conversion does change the waveform, and having now learned a bit
    about perceptual encoding that is the entire point. So... something
    that may have had a peak value of -3 dB as a WAV file probably has a
    different value as an MP2. Not sure how to get around that.

    There is another control file on the unit called PXR4.SEQ, this
    contains the length of the various track files as well as lots of
    other info. I can only reverse engineer this by making similar songs
    where only one parameter is different and compare. So, it MAY be in
    the SEQ file, or it MAY be in the MP2 file. Possibly both.

    Anyway I am going to keep chipping away at this, it would make the
    unit quite a bit more useful and I know that others are interested in
    this functionality as well.
  5. Mike Rivers

    Mike Rivers Guest

    Since the "EG" in MPEG stands for "Expert's Group", I guess we're all
    experts.



    --
    I'm really Mike Rivers - (mrivers@d-and-d.com)

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