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Thread: SEGA CD simple audio tech question

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    King of the Ring WCPO Agent ThugsRook's Avatar
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    Default SEGA CD simple audio tech question

    how does SEGA CD (real hardware) handle the 2 second pre/post gap?
    ive read/know that "space" is needed for seeking, but is it used during playback?



    if someone would be nice enough to help me, i have a simple way to test this...

    North American SEGA CD (real hardware)
    North American Sonic CD (real disc, no CD-R stuff)

    fire up Sonic CD and start a new game. dont play, just sit there and listen to the audio track. at 1:44 the track should end, loop, and restart at 1:47.


    if someone could verify that for me id really appreciate it
    TIA

    (ill gladly explain more of what im getting at, but i need that verified first)

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    YM3438 Master! ESWAT Veteran evildragon's Avatar
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    Those 2 second things are determined when the CD is encoded, it's adjustable, so I'm fairly certain it does abide by this, as fast as the 1X drive can, because it DOES need to re seek at the beginning of the track.
    Customized Sega Genesis Model 1 - VA3. Energy efficient with buck converters instead of LM7805's.


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    King of the Ring WCPO Agent ThugsRook's Avatar
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    Quote Originally Posted by evildragon View Post
    Those 2 second things are determined when the CD is encoded, it's adjustable, so I'm fairly certain it does abide by this, as fast as the 1X drive can, because it DOES need to re seek at the beginning of the track.
    thats why i need to verify.

    i have already fixed this in emulation, but im curious about the real hardware's default behavior.


    can anyone run that test for me?
    that will tell me EXACTLY what i need to know

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    ding-doaw Raging in the Streets tomaitheous's Avatar
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    Understanding what the pregap is for and how it works in relation of, then it's pretty safe to assume that the SegaCD is not playing audio inside the 2 second pregap for track play mode. Btw, 2 seconds is the minimum and default size; it can be larger (legally according to spec). I think the only exception would be if track play mode had an ending track # other than the start (like a normal CD player) so playing through/across tracks sequentially would include the pregap in the CDDA playback, or if the BIOS took LBA addressing or MM:SS:FF addressing argument for the starting point for CDDA playback.

    What is it that you're trying to do, exactly?

  5. #5
    King of the Ring WCPO Agent ThugsRook's Avatar
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    Quote Originally Posted by tomaitheous View Post
    Understanding what the pregap is for and how it works in relation of, then it's pretty safe to assume that the SegaCD is not playing audio inside the 2 second pregap for track play mode. Btw, 2 seconds is the minimum and default size; it can be larger (legally according to spec). I think the only exception would be if track play mode had an ending track # other than the start (like a normal CD player) so playing through/across tracks sequentially would include the pregap in the CDDA playback, or if the BIOS took LBA addressing or MM:SS:FF addressing argument for the starting point for CDDA playback.

    What is it that you're trying to do, exactly?
    KEGA Fusion plays the pregap as a postgap, noticable on tracks that loop. (Using a real Sonic CD, bin+cue, iso+wav, all formats)

    I'm curious if real hardware does the same. youd think it wouldnt with all the trouble thats gone into marking pre/post gaps / end of tracks, etc. unfortunately im thinking real hardware is also gonna play the pre/post gap

    if someone would run that Sonic CD test that i posted earlier... that will tell me exactly what i need to know.

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    King of the Ring WCPO Agent ThugsRook's Avatar
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    Quote Originally Posted by ThugsRook View Post
    if someone would be nice enough to help me, i have a simple way to test this...

    North American SEGA CD (real hardware)
    North American Sonic CD (real disc, no CD-R stuff)

    fire up Sonic CD and start a new game. dont play, just sit there and listen to the audio track. at 1:44 the track should end, loop, and restart at 1:47.
    please, if someone could verify that for me id really appreciate it
    this is all i need to know.
    TIA

  7. #7
    The medium-sized mang. Raging in the Streets Lastcallhall's Avatar
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    I'll look and see if I have my original Sonic CD tonight and test that out if I do.

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    The medium-sized mang. Raging in the Streets Lastcallhall's Avatar
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    Just a quick update - I don't have my sonic disc any longer, it would seem. I tore my loft apart looking for it and I've come to the conclusion that either the cats ate it, or it became part of a larger mess that seems to be growing daily up there... Sorry.

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    Whuff! Outrunner Jax184's Avatar
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    How could a Genesis forum be this useless? I've got 2 CDXs and about 6 Sega CDs. I'll plug one in and do it for you later this afternoon.

  10. #10
    King of the Ring WCPO Agent ThugsRook's Avatar
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    Quote Originally Posted by Lastcallhall View Post
    Just a quick update - I don't have my sonic disc any longer, it would seem. I tore my loft apart looking for it and I've come to the conclusion that either the cats ate it, or it became part of a larger mess that seems to be growing daily up there... Sorry.
    NP ~ thx for the effort

    hopefully JAX will come thru with some results. (thx JAX)

  11. #11
    Whuff! Outrunner Jax184's Avatar
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    Here we go, slightly later than expected. In addition to having to find my CDX power adapter, I had to find my copy of Sonic CD. Turns out both were with my other CDX.

    I made you a recording of the entire sequence, from cold start to just after the first loop.
    http://www.jax184.com/Sonic%20CD%20first%20loop.mp3

  12. #12
    King of the Ring WCPO Agent ThugsRook's Avatar
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    Quote Originally Posted by Jax184 View Post
    Here we go, slightly later than expected. In addition to having to find my CDX power adapter, I had to find my copy of Sonic CD. Turns out both were with my other CDX.

    I made you a recording of the entire sequence, from cold start to just after the first loop.
    http://www.jax184.com/Sonic%20CD%20first%20loop.mp3
    thank you very much

    adjusting for time index, song faded out @ 1:44 and restarted @ 1:45. (compared to my 1:44-1:47 KEGA & real Sonic CD)

    this means real hardware does NOT play pregaps.
    this also means KEGA fusion DOES play pregaps. (bug!)

    thx again

  13. #13
    King of the Ring WCPO Agent ThugsRook's Avatar
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    ok, so KEGA fusion has a verified SEGA CD bug
    this means ALL current BIN+CUE, ISO+WAV, and even home rips... are somewhat incorrect for emulator use

    since PREGAP info doesnt work ~ all of the audio tracks need to be shortened by 2 seconds (some games its 1.74 seconds).

    this can be done by ripping the BIN+CUE to ISO+WAV (or MP3) with IsoBuster, ommiting the pregaps.
    IsoBuster is the only program i know of that can do this. cant be done from real discs, must be BIN+CUE.


    i know i know, ive got balls claiming everything weve been doing for so many years is potentially wrong

    id appreciate it if someone was interested in checking out my claims, trying my repair methods, and testing the results
    Last edited by ThugsRook; 09-30-2011 at 03:00 PM.

  14. #14
    Hero of Algol kool kitty89's Avatar
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    Isn't there an extra requirement for pre/post-gaps for CD-DA located outside of the normal data range of the Sega CD? (I forget what the specific limit is . . . 50 some minutes, or maybe the full 63 minutes of early/low density CDs)
    6 days older than SEGA Genesis
    -------------
    Quote Originally Posted by evilevoix View Post
    Dude it’s the bios that marries the 16 bit and the 8 bit that makes it 24 bit. If SNK released their double speed bios revision SNK would have had the world’s first 48 bit machine, IDK how you keep ignoring this.
    Quote Originally Posted by evilevoix View Post
    the PCE, that system has no extra silicone for music, how many resources are used to make music and it has less sprites than the MD on screen at once but a larger sprite area?

  15. #15
    King of the Ring WCPO Agent ThugsRook's Avatar
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    Quote Originally Posted by kool kitty89 View Post
    Isn't there an extra requirement for pre/post-gaps for CD-DA located outside of the normal data range of the Sega CD? (I forget what the specific limit is . . . 50 some minutes, or maybe the full 63 minutes of early/low density CDs)
    im not sure about that.

    but either way i dont think pre/post gap info is ever gonna work while using "data tracks" anyway.
    Steve might get it working when using a real SEGA CD in KEGA Fusion, but data (audio) tracks are gonna be another animal entirely.

    so ~ we need to correct the audio tracks for proper emulator usage.

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