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Cassettes - Dobly B, C, MPX or none ?
Xrcr9709
post Jan 5 2013, 17:37
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Hello,


I have some cassettes I would like to digitalise. I would like to do it in an "optimal" way so that I won't want to do it again later.
They have been recorded on various recorders which I don't have anymore, and with Dolby deactivated.
I have bought an second hand Denon DRM-400 which seems to me like a goo quality/price ratio (couldn't get a 3-head model)

I have read somewhere that if you have recorded your tape with dolby B, you should use Dobly B or C to play it back, and if you have used Dolby C, you should only use Dolby C to play it back.

Now, what about tapes that were not recorded with Dolby ?


Thank you
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bryant
post Jan 5 2013, 18:43
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The rule is that you should play the tapes back with the same Dolby setting as was used for recording, so if these were recorded without Dolby then you want to have that off for playback.

If the hiss bothers you with the Dolby off, then I would suggest looking at reducing it after you have digitized them...there are some pretty good algorithms for that that will work better than the Dolby on your deck.

As for the MPX filter, that was generally for recording from FM and should not make a difference during playback.
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Glenn Gundlach
post Jan 5 2013, 18:47
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QUOTE (Xrcr9709 @ Jan 5 2013, 08:37) *
Hello,


I have some cassettes I would like to digitalise. I would like to do it in an "optimal" way so that I won't want to do it again later.
They have been recorded on various recorders which I don't have anymore, and with Dolby deactivated.
I have bought an second hand Denon DRM-400 which seems to me like a goo quality/price ratio (couldn't get a 3-head model)

I have read somewhere that if you have recorded your tape with dolby B, you should use Dobly B or C to play it back, and if you have used Dolby C, you should only use Dolby C to play it back.

Now, what about tapes that were not recorded with Dolby ?


Thank you


You would play the non Dolby encoded tapes with the playback Dolby decoder turned off. You do not want to play a 'B' encoded tape with a 'C' decoder or vice versa. This assumes the deck is operating correctly.

G
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AndyH-ha
post Jan 5 2013, 20:05
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Are these music or spoken audio? I've recorded many spoken audio cassettes to computer using Dolby B even though they were not produced that way. There is a very worthwhile reduction in tape hiss. As to whether or not the voice might sound slightly different, who cares? Of course, if your goal is to reproduce the original as closely as possible, regardless of whether or not your result is easier or harder to listen to, perhaps you care.

Recording a little both ways, and comparing the results, doesn't cost much. I know, respecting authority rather than making up your own mind is usually desirable, but you probably won't be forced to confess if you decide to reject gospel.
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ktf
post Jan 5 2013, 22:31
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QUOTE (bryant @ Jan 5 2013, 18:43) *
The rule is that you should play the tapes back with the same Dolby setting as was used for recording, so if these were recorded without Dolby then you want to have that off for playback.

Yeah, that's the rule... I have transferred a lot of tapes to the digital domain, but at some point in the heydays of tapes, Dolby B was so common that it was default on most players and could not be turned off. Because of this, a lot of tapes were not marked, Dolby B was just the way to go as everyone did it.

So depending on when the tapes were recorded, not marked means no Dolby or Dolby B, there is no way to tell except listening. Sadly, Dolby B was made to sound acceptable on players that did not have it, so the difference might be hard to tell. The best way to do this is check for every tape which setting you like most, as there simply is no way to tell which processing has been used if it's not written down somewhere.


--------------------
Music: sounds arranged such that they construct feelings.
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mzil
post Jan 5 2013, 23:13
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QUOTE (ktf @ Jan 5 2013, 17:31) *
Dolby B was so common that it was default on most players and could not be turned off...

No deck which used the word or insignia "Dolby B", ever made, had a non-defeatable Dolby circuit with no "off" position.

Even companies that didn't use the name Dolby and had their own form of noise reduction, such as JVC's "Super ANRS" [super automatic noise reduction system] or Dolby's rival dbx ["decibel expansion", although their Type I and II noise reduction systems were complimentary compression/expansion systems akin to Dolby NR, but more profound at the expense of being unlistenable without the circuit in playback] always had an "off" option.
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2Bdecided
post Jan 7 2013, 15:49
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If you transfer the tapes without Dolby, and then subsequently decide you wish you'd used it, you can apply it using software...
http://www.hansvanzutphen.com/tape_restore_live/download/
...it works quite well, though isn't identical to a HW dolby circuit. That software includes other useful things for tape transfers too.

Cheers,
David.
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Arnold B. Kruege...
post Jan 7 2013, 16:10
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QUOTE (Xrcr9709 @ Jan 5 2013, 11:37) *
Now, what about tapes that were not recorded with Dolby ?


Then Dolby is obviously irrelevant and should be avoided.

Seems obvious enough!

I too am unaware of any tape player that had non-defeatible Dolby.
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Specy
post Jan 7 2013, 23:20
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But you could still use a program like Tape Restore Live to fix lots of other tape issues (such as AZIMUTH problems, temporal volume/highs loss on a single channel, FM stereo hiss removal for recordings from the radio etc.)

By the way, if the tapes are recorded with Dolby B on, I've noticed a vast improvement in audio quality by first feeding the audio (without using Dolby B during playback) through Tape Restore Live's restoration filters and using the Dolby B implementation in it over using Dolby B during playback - most problems with the tape are made worse if you play them back using Dolby B, so if you fix them first you get a much better result.

On top of that, to my big surprise, the Dolby B chip on my (at the time very expensive) cassette deck caused some weird artifacts for very soft sounds, which don't occur when you use the Tape Restore Live implementation. I actually never noticed this until I made some very soft recordings to compare the audio from Tape Restore Live against that of my cassette deck. I assume that this is not the case with older (analog) versions of Dolby B...
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Glenn Gundlach
post Jan 8 2013, 02:15
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QUOTE (Specy @ Jan 7 2013, 14:20) *
But you could still use a program like Tape Restore Live to fix lots of other tape issues (such as AZIMUTH problems, temporal volume/highs loss on a single channel, FM stereo hiss removal for recordings from the radio etc.)

By the way, if the tapes are recorded with Dolby B on, I've noticed a vast improvement in audio quality by first feeding the audio (without using Dolby B during playback) through Tape Restore Live's restoration filters and using the Dolby B implementation in it over using Dolby B during playback - most problems with the tape are made worse if you play them back using Dolby B, so if you fix them first you get a much better result.

On top of that, to my big surprise, the Dolby B chip on my (at the time very expensive) cassette deck caused some weird artifacts for very soft sounds, which don't occur when you use the Tape Restore Live implementation. I actually never noticed this until I made some very soft recordings to compare the audio from Tape Restore Live against that of my cassette deck. I assume that this is not the case with older (analog) versions of Dolby B...


I worked with analog Dolby for quite a few years. Dolby make the machine ' more 'of what it is. If it has a high end droop, it has a bigger droop with Dolby. Same is true for a high end boost, with Dolby it will be a bigger boost. It it was 'flat' it will stay flat. That's why in my earlier post I said it applies if the deck is operating correctly.

What I'm saying is I'm skeptical of 'diddling' the signal before it gets decoded but again, if the deck is wrong all bets are off anyway.

G
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mzil
post Jan 8 2013, 02:48
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Can anyone tell me if this Tape Restorer Dolby "decoder" [which I notice comes with a disclaimer at their site noting it is not the real deal] is truly a variable, sliding band of complimentary* dynamic range expansion? Or is it just a simplistic fixed alteration, perhaps nothing more than a high frequency cut [EQ]?

*"complimentary" meaning it is based on, and re-expands, the variable compression applied to the signal during the true Dolby B encoding, not "complimentary" meaning "free". wink.gif

QUOTE
most problems with the tape are made worse if you play them back using Dolby B, so if you fix them first you get a much better result.

Dolby B, the real deal, was so notorious for exacerbating any high frequency loss due to azimuth mis-alignment (and numerous other reasons) that many people actually found leaving it off on playback was overall the better way to go, even if there was more noticeable hiss by not decoding it. You are correct that for it to work right it should be receiving a full bandwidth signal from the get go, so applying corrective measures to the high frequency loss (inevitable in consumer cassette decks) should be applied before Dolby gets decoded.
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Glenn Gundlach
post Jan 8 2013, 04:32
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QUOTE (mzil @ Jan 7 2013, 17:48) *
Can anyone tell me if this Tape Restorer Dolby "decoder" [which I notice comes with a disclaimer at their site noting it is not the real deal] is truly a variable, sliding band of complimentary* dynamic range expansion? Or is it just a simplistic fixed alteration, perhaps nothing more than a high frequency cut [EQ]?

*"complimentary" meaning it is based on, and re-expands, the variable compression applied to the signal during the true Dolby B encoding, not "complimentary" meaning "free". wink.gif

QUOTE
most problems with the tape are made worse if you play them back using Dolby B, so if you fix them first you get a much better result.

Dolby B, the real deal, was so notorious for exacerbating any high frequency loss due to azimuth mis-alignment (and numerous other reasons) that many people actually found leaving it off on playback was overall the better way to go, even if there was more noticeable hiss by not decoding it. You are correct that for it to work right it should be receiving a full bandwidth signal from the get go, so applying corrective measures to the high frequency loss (inevitable in consumer cassette decks) should be applied before Dolby gets decoded.


My guess - and it's only a guess - is the software 'Dolby' B more closely approximates the JVC ANRS. Both boxes are high frequency companders but Dolby uses a sliding turnover point while JVC is fixed.

Your description of bandwidth issues is exactly right and was the main problem with DBx, particularly on LPs _especially_ if warped.

G
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BFG
post Jan 8 2013, 06:07
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QUOTE (2Bdecided @ Jan 7 2013, 08:49) *
If you transfer the tapes without Dolby, and then subsequently decide you wish you'd used it, you can apply it using software...
http://www.hansvanzutphen.com/tape_restore_live/download/
...it works quite well, though isn't identical to a HW dolby circuit. That software includes other useful things for tape transfers too.

Cheers,
David.

Thanks for the tip, as I too am about to start a cassette-to-digital run. Two questions:
(1) Is anyone aware of a relatively cheap Dolby S or SR-capable cassette player? I have a couple of cassettes encoded with S.
(2) How would one go about applying S or SR-type filtering with TapeRestore or a similar program?

(Mods--this may belong as a separate topic. I wasn't sure.)
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2Bdecided
post Jan 8 2013, 14:04
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Tape restore live only does Dolby B.

Applying EQ to "restore" high frequencies* (and digital denoising to remove the hiss!) before using Tape Restore live's Dolby B implementation is very useful. Its dynamic azimuth correction can be very useful too.

* - there was a Yamaha cassette deck with a feature called "play trim" which applied EQ before the Dolby circuit to help with this.

In ideal circumstances (e.g. using the same cassette deck as the tape was originally recorded on, with both still in good condition) I think the cassette deck's own Dolby circuit is preferable.

Be careful of listening too critically - it will remind you what an abomination cassettes are!

Cheers,
David.
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Specy
post Jan 8 2013, 14:46
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The Dolby B implementation in Tape Restore Live does use a sliding scale, I've actually tested it on a lot of different recordings at very different levels and I haven't found a single instance where it sounded different from what it should sound like. You can actually see the scale slide in the GUI (see this image: http://www.hansvanzutphen.com/tape_restore...estore_live.gif ). It's displayed as pinkish stuff on top of the large squares, and in dark blue you can see what gets removed - the whole shape shifts to the right when more highs are present. If your cassette deck still works, a bunch of test tones are included in the download that you can use to precisely calibrate the signal.

In my case, my original cassette deck does still work, but in many cases there were not only constant AZIMUTH errors that you can fix by aligning the tape head, but also 'moving' AZIMUTH issues especially at the start and end of the cassette (probably because the tape gets stretched when you rewind it). Which means that repairing it first really sounded better than using the Dolby B on my cassette deck.

About 'abomination': I was actually VERY surprised with how great my recordings sounded after restoration. Before they sounded crappy, dull, and I heard annoying phasing effects due to those moving AZIMUTH issues. After correction - except for the presence of some hiss - they actually sound surprisingly good - I definitely prefer the sound of my 25-year-old cassettes (after restoration!) over that of most downloaded MP3s and many 'remastered' (and horribly clipped) CD's.


Dolby S is not possible with Tape Restore Live; I also have a bunch of Dolby S recordings, but so far I haven't digitized them.

By the way: Some more hints:
- If you have a cassette deck with Dolby S be careful: I have one too and at the time I was really happy with how much low frequency noise Dolby S removed. But, when I started to digitize my cassettes and played the Dolby B recordings on my old cassette deck on which I originally recorded them, I noticed that my Dolby S cassette deck had far more low frequency noise than the other one. So the big advantage of Dolby S in this case was that it removed noise that wasn't even there on my old deck. So, when you start digitizing tapes, check for this type of issues first!
- The first tapes I restored with Tape Restore Live didn't sound too good. In fact in some respects they sounded clearly worse than the original. After checking several things I eventually discovered that my built-in sound card (!) was so bad it couldn't reproduce the low frequencies on the tape. So CAREFULLY compare the sound of the original tape against what you get in your pc before you start digitizing lots of tapes. Especially watch the bass.
- Also, ALWAYS record to .WAV or a lossy format such as .FLAC. AZIMUTH issues cause havoc in MP3 encoding; you can safely encode to MP3 *after* running Tape Restore Live over it (if you really have to - you still get a considerable quality loss due to how MP3s work). But NEVER do it BEFORE AZIMUTH correction.
- Make sure to correct AZIMUTH on the cassette deck before recording, if needed. If you listen to the output in mono you can clearly hear even very small discrepancies. Tape Restore Live will repair AZIMUTH and - as far as possible - will also restore lost highs due to AZIMUTH alignment issues, but it's intended for small adjustments, and of course raising the highs also increases the hiss from the cassette deck that you use.

This post has been edited by Specy: Jan 8 2013, 14:50
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2Bdecided
post Jan 8 2013, 15:28
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QUOTE (Specy @ Jan 8 2013, 13:46) *
About 'abomination': I was actually VERY surprised with how great my recordings sounded after restoration.
Fair point - it's pre-recorded tapes I've often found to be abominably bad (compared with decent CDs).

The difference between Tape Record Live and one of my deck's built-in Dolby B (IME, YMMV) was that on speech recordings, the hiss level would audibly pump more with TRL than with the real Dolby B circuit. It was quite subtle, and it may have been user error - but I did managed to get results that were near-identical apart from this artefact, so I think I had it aligned correctly (if you can't align the level in TRL properly the results will be hopeless). However, overall I could get better results with EQ+denoise+TRL, so I still used it.

For slightly dodgy tapes with drifting azimuth, it is magic.

Cheers,
David.
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