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Thread: Recovering 144 Cassette Tapes

  1. #11
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    I think the potential issue at hand is that some Dolby NR schemes are based on companding different frequency bands. So, if you encode something at one speed and attempt to decode it at another speed, with everything shifted an octave up or down, it's liable to end up in a different filter circuit than was intended.
    I'm not sure if Dolby C or S work that way, though - 'C' is supposed to be based around two 'B' decoders, but whether they're in series, or parallel with different frequency bands I have no clue. Obviously if this is B or DBX encoded it's kind of moot anyway because they have a single band anyhow. In any case, the effects can't be that bad or you wouldn't have varispeed controls on the decks.

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  3. #12
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    Quote Originally Posted by mr average View Post
    any 4 head deck even one that messes up the speed will fix the problem of getting the tapes into digital form on a DAW
    hopefully he finds the same deck with the same speed and avoids it completely.

    either i wasted 5 years of my life in graduate school or you can fix the time problem in a DAW without any issues except sample based errors if you have to up/down sample with too few. imho you are drastically overthinking the problem.
    I'm not overthinking anything...and I didn't have to go to graduate school to know that you can do all kinds of numerical crunching with a DAW.
    I'm concerned about the mechanical aspects of the original deck and the yet-to-be decided upon surrogate deck, operating at a yet-to-be disclosed speed.
    Do we even know at what speed the original deck operated...?

    I'm curious...besides the theoretical considerations...how many times has anyone here taken a cassette tape that was recorded on a high speed deck...played it back at a different speed on a different deck...transferred that into a DAW...and then used the DAW's time stretch and pitch correction to make it sound exactly like it did when it was played on the original deck that it was recorded on...?

    But that really wasn't even what I was talking about.
    I know that if you just focus on the numbers, it's all basic math...but time stretching the audio in the DAW is not the same thing as doubling or halving the original tape speed, and you can only stretch an audio track to a point before it doesn't sound right.
    Again...this is non-graduate school, simple stuff... ...if you record 4 notes played at a tempo with each note 1/4 second apart...and then you want that stretched to last for 2 seconds...it won't sound the same, even if the notes stay on pitch.

    At any rate...I'm a simple guy, I want to see it to believe it, because too much theory sounds good, and then you find out that the audio doesn't sound quite right after it's been sped up, slowed down, time stretched and pitch-shifted into submission...but we are so far ahead of the reality here that starts with first finding an appropriate playback machine or at least trying to figure out what's wrong with the current machine.
    So I'm not really the one overthinking it...let's start with Step 1.

  4. #13
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    Per Teac 144 manual...it runs at double-speed 3 3/4 ips..and it uses Dolby B-type NR...and they even tell you that if you use the provided pitch-shift option of the deck, you can mess with the Dolby.

    TBH...I actually think the first consideration will be...are these cassette tapes from 35 years ago even playable....?...but without a deck, can't know that.

  5. #14
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    Quote Originally Posted by miroslav View Post
    I'm not overthinking anything...and I didn't have to go to graduate school to know that you can do all kinds of numerical crunching with a DAW.
    I'm concerned about the mechanical aspects of the original deck and the yet-to-be decided upon surrogate deck, operating at a yet-to-be disclosed speed.
    Do we even know at what speed the original deck operated...?

    I'm curious...besides the theoretical considerations...how many times has anyone here taken a cassette tape that was recorded on a high speed deck...played it back at a different speed on a different deck...transferred that into a DAW...and then used the DAW's time stretch and pitch correction to make it sound exactly like it did when it was played on the original deck that it was recorded on...?

    But that really wasn't even what I was talking about.
    I know that if you just focus on the numbers, it's all basic math...but time stretching the audio in the DAW is not the same thing as doubling or halving the original tape speed, and you can only stretch an audio track to a point before it doesn't sound right.
    Again...this is non-graduate school, simple stuff... ...if you record 4 notes played at a tempo with each note 1/4 second apart...and then you want that stretched to last for 2 seconds...it won't sound the same, even if the notes stay on pitch.

    At any rate...I'm a simple guy, I want to see it to believe it, because too much theory sounds good, and then you find out that the audio doesn't sound quite right after it's been sped up, slowed down, time stretched and pitch-shifted into submission...but we are so far ahead of the reality here that starts with first finding an appropriate playback machine or at least trying to figure out what's wrong with the current machine.
    So I'm not really the one overthinking it...let's start with Step 1.
    he should know what speed the original was at
    or even what the new deck runs at -- although that would help a lot
    but still irrelevant
    if he knows how long the original track was
    that is sufficient to restore the proper speed

    as long as the heads track the right tracks then the speed is irrelevant
    there is NO PITCH CORRECTION! at all
    when you fix the speed it all comes out in the wash less any digital up/downsample artifacts
    and possibly the high end response based on different tape speeds

    when the tape plays it back at the wrong speed
    the DAW does not care about the speed
    you set the start and stop point to be the same as the original would have been
    this has NOTHING TO DO WITH TEMPO OR PITCH
    you set the length the same and then play it normally
    a close analogy would be compression and decompression of zip files


    i have done it
    it works
    try it for yourself and see
    it works
    it sounds right after it has been put back to the correct speed
    this has nothing to do with time stretching pitch or anything else
    of course playing it at the wrong speed will sound different

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    Quote Originally Posted by gecko zzed View Post
    Additionally, recording at double the speed will, as you say, raise the pitch an octave and halving the speed in the DAW will return it to the correct speed, but this will also give you the original formant.
    exactly

    you dont to mess with pitch correction or worry about tempo or anything else

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    Again...you're proving the math works...which is not what I'm even debating, other than when you brought up time stretching.
    I mean, it's basic math, like I said.

    What I'm talking about are the "if" and the "should" and the "as long as"...and the differences in tape deck transport functionality between the original deck and whatever other deck will be used...never mind any DAW resampling artifacts.

    The other consideration is what's the intent of the OP with this...to simply get anything he can salvage off the old tapes, in which case quality may not be a real issue if he plans to rerecord the material but needs the old tape tracks for reference...
    ...or is it to do a perfect transfer without any degradation of any type so he can use them....and would the OP even understand the whole process?

    Oh...and there actually IS pitch correction/adjustment happening...because when you play a high speed tape on a normal speed deck, it will play back slower, which is a different pitch....then you have to get it back to the original pitch in the DAW. So you are in fact manipulating the pitch twice.

    But we are again going well ahead of where the OP is at....so let's wait for him, and then do Step 1.
    I also doubt he knows the *exact* length of each track/song on these tapes to be able to set the start/end points in the DAW after transfer.

    I know that you and I both understand the fundamental math and process...but we are also looking at the whole thing from two different perspectives.

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    Quote Originally Posted by miroslav View Post
    Again...you're proving the math works...which is not what I'm even debating, other than when you brought up time stretching.
    I mean, it's basic math, like I said.

    What I'm talking about are the "if" and the "should" and the "as long as"...and the differences in tape deck transport functionality between the original deck and whatever other deck will be used...never mind any DAW resampling artifacts.

    The other consideration is what's the intent of the OP with this...to simply get anything he can salvage off the old tapes, in which case quality may not be a real issue if he plans to rerecord the material but needs the old tape tracks for reference...
    ...or is it to do a perfect transfer without any degradation of any type so he can use them....and would the OP even understand the whole process?

    Oh...and there actually IS pitch correction/adjustment happening...because when you play a high speed tape on a normal speed deck, it will play back slower, which is a different pitch....then you have to get it back to the original pitch in the DAW. So you are in fact manipulating the pitch twice.

    But we are again going well ahead of where the OP is at....so let's wait for him, and then do Step 1.
    I also doubt he knows the *exact* length of each track/song on these tapes to be able to set the start/end points in the DAW after transfer.

    I know that you and I both understand the fundamental math and process...but we are also looking at the whole thing from two different perspectives.



    you are quibbling whether digital really equals the analog again

    any pitch correction that happens is incidental to the speed change
    i am not manipulating the pitch but changing the speed twice
    you can , at least my DAW and gear can, change the pitch at the same speed

    if he does not know the exact length there might be some trial and error
    or else he can spot a note he knows and see what happened to it to figure out what to change to undo that


  9. #18
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    Quote Originally Posted by mr average View Post
    you are quibbling whether digital really equals the analog again
    Nope...not at all.
    I'm talking mostly about the analog side...which you've sorta left hanging with the "if", "should", "as long as"...and you're just restating the math capability of the digital side, as though it will magically fix all the analog side potential issues using simple math.

    When you have all the known quantities in front of you...it's easy to compute...but when much of it is dependent on "something" you don't know yet...I'm not one to just assume it will al be perfect anyway, and if it's not, we can just massage it and fudge it into perfection because a DAW can do anything.

  10. #19
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    Quote Originally Posted by miroslav View Post
    Nope...not at all.
    I'm talking mostly about the analog side...which you've sorta left hanging with the "if", "should", "as long as"...and you're just restating the math capability of the digital side, as though it will magically fix all the analog side potential issues using simple math.

    When you have all the known quantities in front of you...it's easy to compute...but when much of it is dependent on "something" you don't know yet...I'm not one to just assume it will al be perfect anyway, and if it's not, we can just massage it and fudge it into perfection because a DAW can do anything.
    let me just say that i have done it
    others have done it
    it is not that big a deal to do it

    perfection is not possible
    tape is very imperfect
    changing speed will cause issues with tape if the new deck is different from the original
    up/down sampling will cause minor changes

    he wants his old recordings back
    so as you note he needs to find some 4 track cassette to play them with
    then i claim the rest is not hard to do and he wont tell the difference unless he is a golden ear type
    and he wont care unless after cassette he suddenly got religion about shortcomings in the audio

  11. #20
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    Quote Originally Posted by mr average View Post
    let me just say that i have done it
    others have done it
    it is not that big a deal to do it
    Never said it was.
    I'm also pretty sure your situation didn't have as many "unkowns" as the OP's...which makes things a lot easier.

    Quote Originally Posted by mr average View Post
    perfection is not possible
    tape is very imperfect
    changing speed will cause issues with tape if the new deck is different from the original
    up/down sampling will cause minor changes
    That is what I was talking about. You can't fix that shit in the DAW...it doesn't posses magic powers.

    Quote Originally Posted by mr average View Post
    he wants his old recordings back
    so as you note he needs to find some 4 track cassette to play them with
    then i claim the rest is not hard to do and he wont tell the difference unless he is a golden ear type
    and he wont care unless after cassette he suddenly got religion about shortcomings in the audio
    We can only assume what his intent is and how critical any of this needs to be.
    Will he ever come back and tell us what the problems are with his deck and what's he planning to do with the tracks....?
    I'm still betting the tapes don't even play all that well after 35 years. I've seen it happen all to often with cassettes, because as you say, they have a lot of shortcomings.

    So what high-speed deck did you have tapes from that you had no choice but to play on a different speed deck into a DAW...?

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