The use of dolby when transferring tapes to digital format...

[Sosabba]

Hi all

I've got a bunch of audio cassettes (compact) that I want to record to wav (and maybe later put onto CD).

The tape player I have to do this with is a Technics RS-AZ6 and it offers Dolby B and C. Aside from lending itself to a good gaff in Spinal Tap, I know little to nothing about Dolby.

Can anyone tell me whether they think I should have Dolby on or off during playback when recording the tapes to my PC?

Many thanks

Max

PS - any other tips welcomed!

[Hugh Robjohns]

If the tapes were encoded with Dolby C then you have no choice but to use Dolby C on replay -- if you don't they will sound very strange indeed. However, if the Dolby C decoder replay alignment isn't accurate they'll sound pretty odd too. Some machines provide a user replay level trim control to optimise the Dolby tracking.

If the tapes were recorded with Dolby B, you have the choice of using or not on replay. Leaving Dolby B off will give a slightly brighter sound, but this is usually more than compensated for by the inherent self-erasure that afflicts old cassette tapes. Switching Dolby B on will reduce the hiss, but will also make the sound a little duller than it probably should have been...

Of course, the dullness and/or hiss can be dealt with after the transfer using the usual DAW processing tools, and I'd advise experimenting to see what combination works best.

I generally transfer Dolby B cassettes with the decoder switched off, and then de-hiss in the DAW using iZotope RX2.

H

[Sosabba]

Thanks Hugh for the lightning fast and very helpful response.

I think I will go for the Dolby B off approach and record them raw, so to speak. Then - like you say - I have the option to try my hand at restoration and clean up after the fact. At least then if I balls that up (or get better at it over time) I will still have the raw files to try the process again on.

As for Dolby C, when you say "strange" sounding on playback, what kind of strange do you mean? I can then listen out for it and if I think I'm hearing it I can see whether engaging Dolby C makes things sound better....

Thanks again

Max

[Exalted Wombat]

Can anyone tell me whether they think I should have Dolby on or off during playback when recording the tapes to my PC?

Clean the tape heads thoroughly - it's amazing how much crud can build up on a little-used cassette machine. Check, and adjust if necessary, the playback speed. (It's under that little hole in the motor housing.) Check that the rubber bits haven't deteriorated enough to add unacceptable wow and flutter. Align the heads for maximum top end. Then whichever sounds best.

[Sosabba]

Thanks EW, I'll look into how to do those things.

If anyone out there is a fan of tapes, tape players, etc., I'd be interested to hear which you would choose to use between:

Panasonic 618 -
Panasonic (Technics) 618 Vintage Cassette Deck/ Player/ Recorder. Audiophile. | eBay

Technics - RS-AZ6 -
Technics RS-AZ6 Stereo Cassette Deck

Not a biggie, just curious.

Cheers

[ken long]

I'd look at a Tascam 122Mk2 or 3 or a Nakamichi deck. The Tascam's head screws can be easily accessed and some Nakamichi's have automatic azimuth.

[ken long]

Tascams have Dolby B and Dolby C - can't remember if the Nakajima has NR.

[Tomás Mulcahy]

Thanks EW, I'll look into how to do those things.

If anyone out there is a fan of tapes, tape players, etc., I'd be interested to hear which you would choose to use between:

Panasonic 618 -
Panasonic (Technics) 618 Vintage Cassette Deck/ Player/ Recorder. Audiophile. | eBay

Technics - RS-AZ6 -
Technics RS-AZ6 Stereo Cassette Deck

Not a biggie, just curious.

Cheers

A three head offers better recording quality, otherwise I would guess there's not much to choose between them.

Clip of the cover of the cassette tray so you can access the azimuth screw for the head. With the heads cleaned, listen to the stereo output of the tape summed to mono, and adjust the screw for maximum treble. You have now matched the machine to the tape.

[ramthelinefeed]

I can't believe nobody's invented a Dubbly B/C decoding plugin

[Sosabba]

I can't believe nobody's invented a Dubbly B/C decoding plugin

"Dubbly B/C"??? How about Dubbly D to filter the hiss from the Marshall when it's on 11?

[Exalted Wombat]

If anyone out there is a fan of tapes, tape players, etc., I'd be interested to hear which you would choose to use between:

Panasonic 618 -
Panasonic (Technics) 618 Vintage Cassette Deck/ Player/ Recorder. Audiophile. | eBay

Technics - RS-AZ6 -
Technics RS-AZ6 Stereo Cassette Deck

Whichever was in better condition.

[Hugh Robjohns]

As for Dolby C, when you say "strange" sounding on playback, what kind of strange do you mean?

Dolby C is a far more aggressive noise reduction system, and if the decode threshold isn't set right the result is a muffled sound during quiet bits, which then suddenly gets brighter and more natural during loud sections and transient peaks. it is very obviously 'wrong'

You can read more on the theories and workings of Dolby's domestic noise reduction systems (Dolby B, S and S) HERE

H

[Smellthevalve]

I can't believe nobody's invented a Dubbly B/C decoding plugin

wouldn't they have to pay a huge license?
Anyway I had good results transferring off an old tape using a nakamichi a while back (dolby b)

[Tomás Mulcahy]

This topic comes up so often, maybe SOS could do an article with an archivist, with a boxout on their tricks for cassettes?

I can't believe nobody's invented a Dubbly B/C decoding plugin

I suspect the licensing would be expensive compared to the number of people prepared to buy the plugin. And I would imagine that a pro would already have Cedar or similar, wichi would sort it all out anyway.

Cassette tape is so crap anyway that 99% of the time it sounds better with Dolby B off- as Hugh often points out that's compensating for the self erasure. You will likely have to eq the material afterwards to make it sound "normal" but that treble boost is very very useful. Dolby C is a PITA, you have to find where the trimmers are to adjust the level into the decoder, and do that adjustment by ear (you should do that with B as well but I never bothered). I've never come across an S encoded tape. Finally, with most machines doing the NR on the deck, rather than on a plugin, helps reduce the noise in the electronics.

[James Perrett]

I can't believe nobody's invented a Dubbly B/C decoding plugin

I don't think any of the major noise reduction systems have decoding plugins. I certainly couldn't find one for DBX when I needed one.

As Tomas has already said, one of the most important things is to match the azimuth popping off the head cover and tweaking the exposed screw head. Usually the screw to adjust is obvious but don't go adjusting it too far. A quarter turn one way or the other is usually enough.

Most cassette decks also have a level preset before the Dolby decoder and turning this up slightly can help compensate for the lack of treble in the decoded output as it fools the decoder into letting more high frequencies through. I find the compressed washy cymbal sounds from a non decoded Dolby B tape to be annoying but that's probably just me.

James.

[Tomás Mulcahy]

Tascam seemed to use dbx to compensate for the noisy electronics in both their cassette and open reel machines. So always best to do that on the deck IMO. Which is odd, because the 122 is not particularly noisy but the 38 and most of their cassette four tracks were.

I find the compressed washy cymbal sounds from a non decoded Dolby B tape to be annoying but that's probably just me.

Yes, it is but judicious use of eq usually sorts out the washiness, and I am a big Beatles fan so the compression sounds normal to me.

[Pat Nghia Long]

You can read more on the theories and workings of Dolby's domestic noise reduction systems (Dolby B, S and S) HERE

H

Thank you so much for the link to that document.
Regards,

[vinyl_junkie]

Personally I wouldn't get a Panasonic/Technics tape deck, the latter ones (mid/late 90's) were cra*py from my experience with noisy playback amps. And the earlier good ones all probs could do with a service.
The RS-AZ6 though does have a Laser Amorphous head though whilst earlier Technics machines will all probs have worm (by now) permalloy heads.

As some one suggested above something like a Nak or even pro Tascam would be a better choice

I still have a Technics tape deck but it's electronics have been modified and also has different new old stock Cannon sendust heads...
I didn't pay a lot for it so I'm quite happy, and it sounds like.... http://www.youtube.com/watch?v=K5fYeEXWPp8

Also I'd take the stuff on ebay with a pinch of salt

[Tim Gillett]

This topic comes up so often, maybe SOS could do an article with an archivist, with a boxout on their tricks for cassettes?

Finally, with most machines doing the NR on the deck, rather than on a plugin, helps reduce the noise in the electronics. [/quote]

Not sure what you mean here. Within the frequency band in which the Dolby is designed to reduce noise, not decoding with the machine's decoder will put less demands on the S/N performance of all those stages post the machine's decoder. So an external processor would in this case perform better potentially.

The whole area of decoding NR encoded cassette tapes is fraught with potential difficulties, some of which have been mentioned. Before NR cassettes came along, Dolby was already successfully entrenched in pro recording facilities. Not only did they use wide track, high speed pro tape machines but at their best they aligned them, recording alignment tones to each tape recorded. Even if the tape had not been recorded quite to spec, it could be potentially realigned pre the decoder using the tape's alignment tones.
Decoding a professionally recorded reel to reel tape should therefore much easier than with a cassette. With cassettes, most consumers were using a noise reduction system that even many professional audio people would have struggled to make work properly.

I worked on a state government project digitizing 7000hours of cassettes. One of the problems was that even on some of the tapes that obviously had some sort of encoding, from a listening test, there was no indication of that, or which type was used, on the cassette or in accompanying notes. Even correctly identifying between no NR, Dolby B and Dolby C recordings, just using listening, is probably beyond most people's abilities, at least without some listening skills training.

It's already difficult enough trying to decode Dolby cassettes using just the machine's own decoder. I have personally modified machines so that I can adjust pre decoder gain and EQ. The advantage of this is that you have a reference point which is the properly calibrated playback machine. You always know from how far you are deviating away from that reference, and can return to it at any time. I've successfully Dolby B decoded many cassette tapes using this modification and with trained listening skills.
Once you digitise the cassette, unless you make an accurate note of the playback reference levels, which translate into your digital file's levels, trying to decode using a plugin, even if it were available, would be very difficult.

Contrary to many assertions otherwise, a Dolby B encoded original cassette recording can sound quite good, and a big improvement on no Dolby B. Using a software or hardware denoiser can never hope to approach the true linearity of the signal the machine was recording because both Dolby B and C were quite unusual in their encoding. As well, they were a calibrated system, where the frequency response and level of the playback system had to accurately mirror the recording, far more so with Dolby C, but even B had to be carefully set up too.

Im my experience proper decoding of Dolby B and C tapes, especially C, usually requires specialised gear and specialised listening and equipment operating skills. Not for the faint hearted!

Tim

[Tomás Mulcahy]

Well Tim, that is exactly the sort of thing we want to learn about, from an experienced archivist. Thank you!

[Tim Gillett]

My pleasure. Looks like a great audio forum. I'm already learning lots myself from it.

Tim