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Topic: Decoding Dolby on master cassettes for transfer (Read 8881 times) previous topic - next topic
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Decoding Dolby on master cassettes for transfer

20 years ago, I had a recording setup and recorded live music.  Lineage:  Shure SM81 mics>Peavy phantom power>Sony D6 cassette recorder.  Some of the shows I recorded were encoded in Dolby B and C.

I just purchased an ADC (TC Electronics Impact Twin with firewire connection) and am digitizing the cassettes onto my computer.  I am transfering them with a Nakamichi DR-2 cassette deck using Kimber Silver Streak cables at 16/44.1 with Audacity.

Question:  decoding the tapes with Dolby on the cassette deck is producing recordings that are a little dull and seem to be phasing in and out some.  I am new to transfering, are there any rules of thumb in this case?  Should I leave Dolby off?  Are there plugins for Audacity that would decode Dloby better than the cassette deck?  Should I be using a different program than Audacity? 

I understand that sound is subjective, and I should just try different combinations to reveal the best results.  But I am new to transfering analog into digital, and would really appreciate some rules of thumb in doing this.  I don't want to reinvent the wheel.

Thank you for any and all comments.

(I did clean the cassette heads multiple times with 99% alcohol, and the deck does play well.  Maybe the phasing is because I didn't encode the cassettes originally though the cassette is marked Dolby?)

Decoding Dolby on master cassettes for transfer

Reply #1 –
You could be having an issue with head azimuth adjustment. It is also possible that after 20 years the recordings have degraded.

Decoding Dolby on master cassettes for transfer

Reply #2 –
PDQ´s statement is very valid: due to old age of the cassettes they have probably degraded by now. The phasing may be one of the indices for this (the band itself possibly was exposed to heat / never used for several years and therefore "twisted"). We can rule out the Nakamichi since it reduces the stress for the band by using a Tape pad lifter. The dull sound could result in deteriorating magnetic information on the cassette band or because (more probable) of wrong azimuth alignment. If the tapes did degrad there may be the possibility of "baking" them - this is at least what is done to older mastering tapes. They are, I admit, technically different but I´ve read about companies that can restore them but it is costly.

What types of Cassettes did you use with your portable Sony? I still have some very old cassettes which still play fine (Sony Metal Master).

And if you plan to transfer them without using Dolby during playback... I have read somewhere that Dolby B can be reproduced quite easily with certain EQ adjustments but that it´s more difficult with Dolby C. The noise reduction you used should be very easy to find out - a recording done with Dolby C has a "distortion" that sounds like dynamically altered reverb when played back with Dolby B and sounds kind of harsh. A recording done with Dolby B and played back with Dolby C has a "pumping" sound.

P.S.: the Kimber cable won´t gain any benefit at all if you use it with a Cassette deck.
marlene-d.blogspot.com

Decoding Dolby on master cassettes for transfer

Reply #3 –
Quote from: Cavaille on
P.S.: the Kimber cable won´t gain any benefit at all if you use it with a Cassette deck.

...or probably any other piece of audio equipment beyond placebo effect.

Decoding Dolby on master cassettes for transfer

Reply #4 –
An old thread about azimuth and Nak DR-2: http://www.hydrogenaudio.org/forums/index....showtopic=31742

In addition, it might be a good idea to demagnetize the tape heads. Some threads elsewhere on the web:
http://homerecording.com/bbs/showthread.php?t=16230
http://www.diyaudio.com/forums/analogue-so...tape-heads.html
http://www.gearslutz.com/board/geekslutz-f...ng-mishaps.html

Decoding Dolby on master cassettes for transfer

Reply #5 –
For the specific tape I am writing about, it was a TDK SA90.  Not the best medium for a master, nor was the choice for using Dolby.  Otherwise, I used good metal tapes for recording.

I demagnetize the heads prior to the transfer. 

Tape head azimuth was a thought.  I wish I had a tape deck that did this, maybe ebay has a good deal, but I doubt I'll go this far.

Tape degredation - probably.  Although I have only played back my masters a handfull of times, they have been stored in an area that at times probably gets too warm.  I have a radiant floor in my basement where my tapes are stored.  In the winter, the floor can get quite hot.  I realized this a few months ago, and that's why I am transfering my music.  I was hoping it wasn't too late.  I have heard that old tapes can shed a lot of oxide, and am watching the heads and rollers to see if they get excessively dirty.  Nothing out of the ordinary, I don't think I'm at a time where the tapes need to be baked.

Thanks!

Decoding Dolby on master cassettes for transfer

Reply #6 –
Quote from: Alex B on
An old thread about azimuth and Nak DR-2: http://www.hydrogenaudio.org/forums/index....showtopic=31742

In addition, it might be a good idea to demagnetize the tape heads. Some threads elsewhere on the web:
http://homerecording.com/bbs/showthread.php?t=16230
http://www.diyaudio.com/forums/analogue-so...tape-heads.html
http://www.gearslutz.com/board/geekslutz-f...ng-mishaps.html



Interesting Nak link.  I've heard that before: "you should only play tapes back on a NAK that were recorded on a NAK" in regards to their tape head gaps.  I have never tested that theory, but have owned this particular deck for about 17 years.  It hasn't had much use in the last 8 years though.

The demagnetizer I use is a Diskwasher cassette type with rotating magnets in it.  Back when I bought it, it was supposed to be pretty good.  Most important though, other cassettes sound good when played back.

Thanks,

Decoding Dolby on master cassettes for transfer

Reply #7 –
Dolby B is a lightweight and usually foolproof process. Just take the treble down a bit would get you most of the way there. Dolby C is a bit tweaky. I remember having problems if you recorded on one deck and tried to play back on a different one. If you're having problems mostly with Dolby C, it could be a calibration issue. You can calibrate Dolby A but as far as I know, you can't adjust Dolby C.

If you're having periodic (rhythmic) phasing problems with the Dolby B tapes, it may be because the tapes were exposed to a magnetic field - check to see if the phasing rhythm  approximately matches the spinning of the reels.

Decoding Dolby on master cassettes for transfer

Reply #8 –
Quote from: eg68 on
20 years ago, I had a recording setup and recorded live music.  Lineage:  Shure SM81 mics>Peavy phantom power>Sony D6 cassette recorder.  Some of the shows I recorded were encoded in Dolby B and C.

I just purchased an ADC (TC Electronics Impact Twin with firewire connection) and am digitizing the cassettes onto my computer.  I am transfering them with a Nakamichi DR-2 cassette deck using Kimber Silver Streak cables at 16/44.1 with Audacity.


I'm pretty sure that the Kimber cables aren't causing any of the problems that you are observing. Commodity cables are simple things and have no choice but to accurately pass signals. With high end cables you never know.

Quote
Question:  decoding the tapes with Dolby on the cassette deck is producing recordings that are a little dull and seem to be phasing in and out some.


The phasing in or out may be related to the dull sound. I'd focus on the phasing in and out, because if you fix that you can at least fix the dull sound with equalization.

A phasey sound from a tape is due to the tape either being physically deformed, or the playback deck skewing the tape back and forth across the playback head. You should be able to see any actual deformation or excess cupping of the tape if you manually wind the tape down past the leader and see the actual brown or black recorded tape. Of the tape has remained straight, flat and supple, and if it is not depositing oxide onto the tape heads than it is probably OK.

Both tape transports and tape can go bad on the shelf. They can both wear out. How long has it been since you played the tape and on what machine did you last play it, and was it OK?

What happens if you play the tape on a different machine?

If the tape seems fine, and plays well on other machines, then either use the other player, or get the one you have repaired.

Once you have a stable platform for playing tapes, you can correct the dull highs with equalization using either the facilities built into Audacity, or the more sophisticated plug-ins both freebie and commercial that can be easily added to Audacity.

Quote
I am new to transfering, are there any rules of thumb in this case?


People who are really into high quality transfers realign their deck for every tape. Azimuth is almost guaranteed to be suboptimal.

Quote
Should I leave Dolby off?


Probably not.

Quote
Are there plugins for Audacity that would decode Dloby better than the cassette deck?


Probably not. I know of only one program that even pretends to implement Dolby B decoding, and it is a plugin for Winamp:

Winamp Plug In That simulates Dolby B

I've done some technical tests and it seems to to a pretty fair job. The authors reverse-engineered the Dolby-B specs.  I would hope that top cassette deck developers like Nakamichi, using licensed technology could do as well if not better with analog circuits provided those analog circuits were in a good state of repair.

Quote
I understand that sound is subjective, and I should just try different combinations to reveal the best results.  But I am new to transfering analog into digital, and would really appreciate some rules of thumb in doing this.  I don't want to reinvent the wheel.


I don't think you should "try different combinations" as audiophiles seem to be prone to do. I think you should obtain the right tools, learn how to use them, and intelligently adjust them for the best possible audible performance. That is the professional approach. This "trying different combinations" stuff is something that frustrates audiophiles and enriches dealers. Its like shooting in the dark.

You did well when you obtained Audacity, because it can be a powerful tool for what you want to do. If its built-in equalization doesn't do the job, there are a jillion "VSR plug ins" that you can easily and inexpensively add that can be very effective if you learn how to use them.  The first plug in I added to my copy of Audacity was a freeware parmetric equalizer. You might want to do the same.

Quote
(I did clean the cassette heads multiple times with 99% alcohol, and the deck does play well.  Maybe the phasing is because I didn't encode the cassettes originally though the cassette is marked Dolby?)


If you say the deck plays well, then I presume that you mean that it plays other tapes well. That's a good sign that suggests that your problem may be with the problematical tape itself.

Playing Dolby-encoded tapes with Dolby turned off is a cheap and fairly crass way to get more highs.  Dolby is a high frequency equalizer-based system, but unlike a standard equalizer it is dynamic, and boosts the highs on soft sounds more, and may actually back off a shade on loud passages to compensate for the fact that the cassette tape medium has poorer dynamic range at high frequencies. So, the best way to deal with a Dolby encoded tape is usually to decode it as accurately as you can, and then address any remaining issues with missing highs with an equalizer.




Decoding Dolby on master cassettes for transfer

Reply #9 –
Arnold, thanks for a great reply!  I'll answer some of your questions, in order, then look into my issue some more.

- I don't have the tape with me as I write this, but I'm fairly certain it's in good shape.  I know what you mean by the cupping, again I'm fairly certain it's ok.
- I probably last did a transfer of the tape 15 years ago.  I don't have a copy of the cassette that was made from it for a comparison.  I didn't remember issues before.
- I don't have another tape deck at hand, but could try another Nak that a friend has.  Good point, try another machine.  I would like to think my deck is perfect, but machines do wear out.  But other tapes sound good in it....leading to the issue being on the tape.
- Since I don't use the deck on a regular basis, I really should look to see how to adjust the azimuth and then do it for every transfer.  I recorded the tape with a Sony D6, there must be difference in the azimuth.  There must.
- I seems that audio purest don't want people to mess around with equalization, turning Dolby off, etc.  It's probably best that I leave it as is (direct transfer) and then goof around with a "mastered" copy.
- I'll mess around with Audacity some more, I haven't used many of the plug-ins, except fade in/out.
- I find your comment interesting that Dolby doesn't encode in a linear fashion.  This may be exactly what I am hearing as "phasing"

Thank you very much!

Decoding Dolby on master cassettes for transfer

Reply #10 –
Quote from: eg68 on
- I find your comment interesting that Dolby doesn't encode in a linear fashion.  This may be exactly what I am hearing as "phasing"


Maybe, maybe not. Sometimes Dolby magnifies other faults, other times it helps hide them.  Your tests on another good quality tape machine should tell you much.

Decoding Dolby on master cassettes for transfer

Reply #11 –
Quote
- I seems that audio purest don't want people to mess around with equalization, turning Dolby off, etc. It's probably best that I leave it as is (direct transfer) and then goof around with a "mastered" copy.
There's no harm in that...  Occasionally, if I'm doing lots of processing, I'll keep an unaltered "original archive" copy. 

It's not because I'm a purist...  There's nothing wrong with correcting an obvious defect like reducing noise or correcting high-end roll-off.  But, with processes like noise reduction there can be artifacts that I don't notice right away, or sometimes I've just gotten "carried away" and over-done the EQ or something...    Or, if I'm doing something really impure like adding reverb or simulating stereo, then I'll keep an original archive!

Decoding Dolby on master cassettes for transfer

Reply #12 –
Quote from: Cavaille on
PDQ´s statement is very valid: due to old age of the cassettes they have probably degraded by now. The phasing may be one of the indices for this (the band itself possibly was exposed to heat / never used for several years and therefore "twisted"). We can rule out the Nakamichi since it reduces the stress for the band by using a Tape pad lifter. The dull sound could result in deteriorating magnetic information on the cassette band or because (more probable) of wrong azimuth alignment. If the tapes did degrad there may be the possibility of "baking" them - this is at least what is done to older mastering tapes. They are, I admit, technically different but I´ve read about companies that can restore them but it is costly.

What types of Cassettes did you use with your portable Sony? I still have some very old cassettes which still play fine (Sony Metal Master).

And if you plan to transfer them without using Dolby during playback... I have read somewhere that Dolby B can be reproduced quite easily with certain EQ adjustments but that it´s more difficult with Dolby C. The noise reduction you used should be very easy to find out - a recording done with Dolby C has a "distortion" that sounds like dynamically altered reverb when played back with Dolby B and sounds kind of harsh. A recording done with Dolby B and played back with Dolby C has a "pumping" sound.

P.S.: the Kimber cable won´t gain any benefit at all if you use it with a Cassette deck.


As for your 'Baking' idea, I worked at a Hollywood post house where we transferred old 2" videotape. We baked all the reels for 12 hours at 135F using a commercial food dehydrator. You DON'T want to try this with an oven like in your house. We had 100% success and more importantly, 0% failure/damage. Some of the tapes would roll less than 1 foot (at 15 IPS) before sticking to the guides but play perfectly after the bake. It also works on 1/4" audio tapes. For plastic tapes you might want to drop the temp to 120 and just cook longer.

G²

Decoding Dolby on master cassettes for transfer

Reply #13 –
You must set the azimuth to match the original recording when transferring a tape - you're completely wasting your time otherwise.

This step is not optional!


However, tape restore live will not only do Dolby B in software, it will also (try to) correct (small-ish) azimuth errors. It will also let you EQ the tape before the Dolby B processing - important, as any treble loss over the last 20 years will throw off the Dolby decoding - correcting for it before the Dolby circuit works wonders.

I'm sure the Dolby B processing in Tape Restore Live isn't identical to what's in a tape deck, but given the huge advantages of doing it in software (yet another one is that you can de-hiss before Dolby processing!), I think it's worth the slight compromise for the many tapes that will benefit.


Are there really any cassette tapes that need baking?! I don't know - it was mostly specific 1970s reel tapes that had the problem with moisture which baking (temporarily) cures - I don't have many cassettes that old.

Cheers,
David.

Decoding Dolby on master cassettes for transfer

Reply #14 –
Regarding baking, I have recently enjoyed reading many nice articles at wendycarlos.com. In one of the stories Wendy writes about her experiences in rescuing master tapes by baking: http://www.wendycarlos.com/newsold.html#baketape

There is also a "baking recipe" by Eddie Ciletti (edited & expanded by Wendy): http://www.wendycarlos.com/bake%20a%20tape/baketape.html

Decoding Dolby on master cassettes for transfer

Reply #15 –
You should definitely check out Stereotool, which is an update of Tape Restore Live! mentioned in post #9.

It somehow manages to process sound files to correct azimuth errors.  Seems impossible but it appears to work.  Has lots of other setting to fool with too.

I recently tried it on an old cassette and was very impressed.

I agree with the other recommendations here, but this is an easy one to try.

Decoding Dolby on master cassettes for transfer

Reply #16 –
Quote from: gottogo99 on
You should definitely check out Stereotool, which is an update of Tape Restore Live! mentioned in post #9.

It somehow manages to process sound files to correct azimuth errors.  Seems impossible but it appears to work.  Has lots of other setting to fool with too.

I recently tried it on an old cassette and was very impressed.

I agree with the other recommendations here, but this is an easy one to try.



I have only thought of Winamp as an audio player.  It can be used to process music prior to Audacity or actually record?

Decoding Dolby on master cassettes for transfer

Reply #17 –
Quote from: 2Bdecided on
You must set the azimuth to match the original recording when transferring a tape - you're completely wasting your time otherwise.

This step is not optional!


I think I need to agree with you.  I was hesitant to mess around with my deck head for fear that I would screw it up permantly.  But I just found a post that describes how to adjust the DR-2 head azimuth.  I'm going in!

Decoding Dolby on master cassettes for transfer

Reply #18 –
Assuming you don't record on the deck any more, and just use it for transfers, there's not much to "screw up".

True, without a pro alignment tape, you may never get the "correct" alignment back - but unless you're very lucky, that's not the alignment you need for playing most tapes anyway.

btw (and it's probably too late now  ) before you change the alignment, record some mono white noise to tape. That'll be a decent test tape to get the alignment back later if you want to.

Cheers,
David.

Decoding Dolby on master cassettes for transfer

Reply #19 –
Quote from: 2Bdecided on
Assuming you don't record on the deck any more, and just use it for transfers, there's not much to "screw up".

True, without a pro alignment tape, you may never get the "correct" alignment back - but unless you're very lucky, that's not the alignment you need for playing most tapes anyway.

btw (and it's probably too late now  ) before you change the alignment, record some mono white noise to tape. That'll be a decent test tape to get the alignment back later if you want to.

Cheers,
David.


Yeah, it's just turned into a transfer only deck.

In true form, I probably won't be using a calibration tape, but instead will just adjust by ear.  I assume I can do this realtime with my headphones on while playing a tape. 

I will mark the screws with "original placement" lines first so I can get back to normal should things get too outa whack.

Skol

Decoding Dolby on master cassettes for transfer

Reply #20 –
Quote from: eg68 on
I have only thought of Winamp as an audio player.  It can be used to process music prior to Audacity or actually record?

If you download the VST version of Stereotool, you can use it in certain audio editors.  It didn't seem to work in Audacity but it did in Adobe Audition.  Might work in Wavosaur.  You get a nag screen but the VST works.

I don't use Winamp but my understanding is that you can save the file after it's converted.  Not positive though.

Decoding Dolby on master cassettes for transfer

Reply #21 –
You use diskwriter output in Winamp - the output goes to disc, much faster than real time. Nothing is played to the sound card in this case.
 

Decoding Dolby on master cassettes for transfer

Reply #22 –
Quote from: eg68 on
In true form, I probably won't be using a calibration tape, but instead will just adjust by ear.  I assume I can do this realtime with my headphones on while playing a tape.
That's the right way to do it, but it's far easier to find the sweet spot if you convert the signal to mono on the way to your headphones. Makes the cancellation due to incorrect alignment far more drastic, so the correct setting sticks out more.

Cheers,
David.