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What bitrate for S-VHS transfers to Tosh XS32?

Discussion in 'Blu-ray & DVD Players & Recorders' started by Matthew Attoe, Jan 21, 2005.

  1. Matthew Attoe

    Matthew Attoe
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    Hi,

    What would be the best bitrate to use when transferring S-VHS recordings (tv series - about 90 episodes - recorded from UK Gold on Sky, most episodes are in mono and some are in stereo) to be subsequently burnt to DVD-R?

    Apparently the Tosh switches from a full-resolution mode to a half-resolution mode at some point. Does anyone know at what bitrate this happens? Also, as they are S-VHS recordings would I be better to record at a bitrate that falls under the full-resolution range rather than the half-resolution range? Also, which of the 3 audio modes would be the best to use? L-PCM? Or one of the the other two (Can't remember their names at the moment!)

    Basically, I want to be able to acheive the best-quality results without "wasting" dvd space.

    Thanks in advance,

    Matthew
     
  2. redsox_mark

    redsox_mark
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    Matthew,

    This is a tough one to answer exactly. I’ve seen some charts and tools which show a rate of around 3.6-3.8 being “S-VHS quality”. But that doesn’t mean that is what you should use. The higher rate you use, the more accurately your recording will match the original. Obviously you can’t improve on the original, and at higher rates you may not notice any difference (so the bits are “wasted”). But a S-VHS source recorded at 9.2 will probably look better than one recorded at 3.6. But 9.2 would be over the top…. I’d probably start with the SP setting of 4.6… this gives good quality and you can fit 2 hours (using the D/M1 audio). (The XS32 is reported to drop its resolution at ~2 hours 20, which would mean anything under 4.0 uses half resolution, but I haven’t seen that officially documented anywhere). You can experiment, trying a higher or lower rate and see if you notice the difference.

    For audio, use one of the compressed modes – generally the default “D/M1” mode (192K). This leaves you more bits to use for your video. Unless your material is a very high quality music recording (and you got a good ear and high end audio kit) I wouldn’t bother with the other modes. Certainly don’t use LPCM, unless the best possible audio is critical, as that takes up a lot of space, meaning you’d have to use a much lower rate for the video to keep the same duration. Given the material you are recording, defiantly D/M1 (which is the default).

    Mark
     
  3. Matthew Attoe

    Matthew Attoe
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    Thanks for the reply.

    So, 4.0 is still full-resolution and 3.8 is half-resolution? Have I got that right?

    Thanks again,

    Matthew.

    PS Does the xs32 have time-base correction?
     
  4. redsox_mark

    redsox_mark
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    I think so, based on Raaczak’s statement that it drops around 2 hours 20 mins. (Per the bitrate table in the manual, 4.0 is 2:18, while 3.8 is 2:25. But again I have no confirmation of this.

    Time based correction? The UK manual and brochure makes no mention of it, but the US model does.
    http://www.tacp.toshiba.com/tacpassets-images/models/rd-xs32/docs/rd-xs32_spec.pdf

    Mark
     
  5. TobyW

    TobyW
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    My Tosh XS32 seemed at first to produce excellent quality recordings, at settings up to the 3-hour bitrate. I even sent a letter of praise to this forum.

    But when I eventually got around to dubbing from HDD to DVD, the Tosh said the recording mode had not been DVD-compatible (this is the default), and insisted on re-encoding it while dubbing.

    Although the bitrate was still the same, it was painfully obvious that the resolution had changed from full to half. I later found this quality-difference mentioned in the manual, I think it said for bitrates 3.2 to 3.8

    I was already fed up with the Tosh's DVD-R compatibility problems, so at that point I took the Tosh back and got a Panny instead.
     
  6. SDHoward

    SDHoward
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    I had also thought the compatibility should obly effect the sound, however on checking it does say that for a recording of between 3.0 and 3,8, if the mode is on then the picture quality may become lower than when off. Anyone able to explain why.
    BTW I think my defult is On (mode I) so that I'm covered should I want to make a DVD-Video
    Anyway as I've always been in compatibility mode I've never experienced any different, so I'm still happy :)
     
  7. redsox_mark

    redsox_mark
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    Interesting. The XS32 has something called DVD compatible mode, which needs to be set when you make the original recording, otherwise it will have to do a “rate conversion” when writing to DVD-Video.

    The manual doesn’t say anything about half resolution (I’ve searched it carefully, including online searching for keywords). But it does say:

    “When you select the manual rate of the picture quality
    between 3.0 and 3.8 and set this mode to “On (Mode I)” or
    “On (Mode II)”, the picture quality may become lower than
    when you set this mode to “Off”.”


    This seems to be what Toby W was seeing; that if you create a DVD-Video compatible disk with the rate in this range, you will get lower quality.

    This sounds to me like the XS-32 drops to half resolution at 3.8 if DVD compatible mode is on, and 2.8 (i.e. less than 3.0) otherwise. I'm not sure why, but that's what it sounds like!

    Mark
     
  8. bankroot

    bankroot
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    It is interseting :eek:

    seems to me Pioneer has better bitrate at the same time of recording than Toshiba.
    In 2 hours mode Pioneer has 5.2 Mbps and in 140 mins 4.8 Mbps

    bankroot
     
  9. redsox_mark

    redsox_mark
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    This doesn’t make sense. While quality of picture or decision when to drop to half resolution can vary due to quality of the encoder, the formula that relates bitrate to duration is simple math. (I suppose a manufacturer could make a different decision on how full to fit the disk).

    If I ignore the Toshiba table and do the sums, assuming 192K audio, for 2 hours the max rate is 4.896. For 2:01 it is 4.856… the Tosh says 4.6, so it is being conservative.

    But I see no way the Pioneer can fit 5.2 onto 2 hours.. the math just doesn’t fit. Unless when you set the Pioneer to 5.2 the actual rate is less.

    Even with no audio, for 2 hours the max bit rate is 5.088.

    Mark
     
  10. bankroot

    bankroot
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    do you suggest that Pioneer lies ?
     
  11. redsox_mark

    redsox_mark
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    No.

    Bit either they are wrong, or using a different scale. Again, it is simple maths. If the rate really is (e.g.) 5.2, and this means 5200 kbit/sec, then only 1:53 can fit.

    Maybe when the Pioneer says 5.2 they mean something different; like they are assuming a decimal rather than computer definition of a kbit? (e.g. 1000 vs. 1024). This might explain it.

    Again, it is maths. No company can change the simple relation between bit rate and size. They can use different scales to measure it, and they can do lots of things to vary the quality. But they can’t change the maths.

    The basic bitrate formula is

    (Size - (Audio x Length )) / Length = Video bitrate
    L = Lenght of the whole movie in seconds
    S = Size you like to use in KB
    A = Audio bitrate in KB/s
    V = Video bitrate in KB/s, to get kbit/s multiply with 8°.

    °8 bit = 1 byte.
    °1024 = 1 kilo in the computer world.

    Mark
     
  12. bankroot

    bankroot
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    If I can see Mbps I treat it as not as decimal value (big letter).
    As far my info about bitrate from Pioneer recorders it not derived from their official site, but from www.areadvd.de.
    There is a table in every Pioneer recorder review what I am talking about.
    Maybe reviewer is wrong, but this website seems to be very trusty.

    bankroot
     
  13. redsox_mark

    redsox_mark
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    I don’t speak German, and can’t easily see anything there about this.

    I use the widely used Videohelp calculator

    http://www.videohelp.com/calc.htm

    I’m not really too bothered about how Pioneer may define their rates. It just isn’t possible for 2 manufacturers, given the same rate of X, and the same size disc, to have a different duration. If the duration is different, then the rate X must be different.

    I don’t know if the Pioneer is better or worse than the Toshiba. But it is misleading and incorrect to say that somehow the Pioneer can use a higher bit rate for a given time than the Toshiba.

    It is like a tap with water flowing and a bucket underneath. At a given rate of the tap, the bucket will fill up in a given time. One company can do a better job of filtering the water than another, but they can’t change the fact a given rate means a given time for a given size disc.

    Mark
     
  14. bankroot

    bankroot
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    It was not my intention to mislead whoever.
    I am not going to discuss about this subject, because I am not an expert in encoders, I have just mentioned (I remembered this table) what I keep in my mind.

    From the other hand it is quite strange, there is no in this calculator any resolution info (It assumes resolution changing, isn't it?).

    bankroot
     
  15. redsox_mark

    redsox_mark
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    The resolution doesn’t change the simple equation. I.e. no matter what resolution is used, around 4.8 Mbps will fill a DVD is around 2 hours.

    The resolution, in non-technical terms, simply changes how the bits are “spent”. At low bit rates, the manufacturer has to decide what is better: to use a higher resolution (and a less accurate reflection of it), or use a lower resolution (but be more accurate).

    Mark
     
  16. bankroot

    bankroot
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    question to you Mark,

    I have just made an experiment.
    I recorded a few mins of material to HDD and DVD-RW (Video mode) in SP mode (in my Pio 520 it means 2 hr mode).
    When I play recorded material I can see bitrate no screen display (special taste on remote). It is funny, because many times more than 5,2 Mbps appears :rolleyes: (sometimes 6 Mbps on "credit list", sometimes 4,3 or less)

    Tell me, result of bitrate calculator is a max or average ?

    bankroot
     
  17. redsox_mark

    redsox_mark
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    Bankroot,

    When talking about bit rate, it is always the average (if a variable bit rate). Yes for a VBR recording (and I think all of the set top recorders use VBR) the rate at any moment in time will vary.

    Mark
     
  18. bankroot

    bankroot
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    does it mean, if I record in 2 hr mode i.e. "credit list" (where I observe high bitrate, more than 6 Mbps), my recorder will "slow down" bitrate to less value ?

    bankroot
     
  19. redsox_mark

    redsox_mark
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    Yes – if you set your recorder for a bit rate of X (e.g. 5.0), it will attempt to use that 5.0 Mbps on average. It will use a higher rate in some places, and a lower rate in others.

    For this reason the timings which will be supported at any set rate can vary a bit… i.e. if I set the rate to 5.0, maybe the actual rate used is 5.001; the recorders will pretty much meet the average rate you set, but not 100%.

    Mark
     
  20. bankroot

    bankroot
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    thank you very much for your answers and patience :smashin:
     

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