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Digitising Cassettes

Postby BA185 » Wed Apr 08, 2020 2:58 pm

Hello,

I need to digitise some cassette tapes (some are very old) and need the audio to be at the highest possible quality.

I don't appear to have a tape deck to play them from.

Any thoughts on the best (and cheapest) way to go about this would be greatly appreciated. I could send them to a recording studio I've worked with if it's not advisable to DIY it.

Many thanks
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Re: Digitising Cassettes

Postby MOF » Wed Apr 08, 2020 3:31 pm

If you get hold of a good quality cassette player it’s very easy to digitise them yourself.
When I archived my composition tapes I did switch off the Dolby button as it seemed to not accurately mirror the original machine’s Dolby encode circuit.
Make sure you clean the heads before playing each side of the tape(s).
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Re: Digitising Cassettes

Postby desmond » Wed Apr 08, 2020 3:35 pm

To do it best, a pro will align the cassette machine to the tape to get the best from it. So if you really want it done well, it might be worth getting it done professionally.

James Perrett might have some more advice, as he does this kind of thing...
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Re: Digitising Cassettes

Postby resistorman » Wed Apr 08, 2020 3:55 pm

I bought a new cassette deck for my archival project. The key is to adjust the head for each tape since there is no real calibration for decks, and the tracking varied enormously. Also, some spare blank cassettes to use as donor bodies.
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Re: Digitising Cassettes

Postby Tomás Mulcahy » Wed Apr 08, 2020 4:49 pm

What deck did you use resistorman?

Just to add to the already perfectly good advice- Yes, transplanting the reels from a cheap or worn out shell into something decent, makes a big difference. Less wobble, more stable azimuth (even though wobble might already be on the recording) Maxell XLII or better, XLIIS shells were the best ones I think. If you can get a deck that allows you to trim the level into the dolby decoder, the dolby will work better. Or you can leave it off and live with the slightly compressed high end. Which will likely be much less of a problem than the self-erasure. It'll actually compensate for the loss of HF.

To get the "tracking" or head azimuth right, pan the left and right outputs of the cassette to centre. Use a plugin to boost the HF monitoring level. There's a little screw hole at the front of the deck to adjust the angle of the head against the tape. Tweak that til you hear maximum HF. It might me ear-hurtingly bright, that's good. Means you're getting max from the tape. Means L and R are now perfectly in phase. Obvs don't use the HF boost for real.

Bear in mind that the azimuth can vary across the tape- if it was done on different decks, same deck different day, flaws in the cassette shell, flaws in the original deck etc etc. So check it occasionally if it's a long tape.

Make sure to record the leader and all of the "blank" bits of the the tape, so a noise reduction plugin can make a good profile. Save that profile. Then use that as little as possible. You'll probably eq the stuff to liven it up, so load that profile you made and apply NR after the eq (usually best I find). Because the eq is usually lots of HF boost, where the noise will be most obvious.

16 bit 44.1kHz WAV is vastly more dynamic range and bandwidth than any cassette can manage so don't waste time and space with 24/96 or whatever.

If you want to try removing wobble (aka wow and flutter) Celemony Capstan is worth hiring for a few days, after you've got all the other processing done and have decided what you want to clean up.

Tascam, Yamaha, Pioneer, Sansui and Sony all made good decks, there are plenty more, you'll easily find the good ones with a google search.
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Re: Digitising Cassettes

Postby James Perrett » Wed Apr 08, 2020 8:02 pm

There's plenty of good advice from Tomás. Getting things right at source is the most important thing which means checking the pressure pad (they have a habit of dropping off) and adjusting the azimuth. Instead of boosting the treble, I find it easier to switch to mono and adjust for maximum treble. Occasionally this doesn't work due to the head gaps in the recording machine not lining up but usually this works much better than listening in stereo. If the head gaps don't line up, I've created my own JS plug-in in Reaper to delay the channels slightly (or you could use Themeo's Stereotool to automatically adjust the channel delay).

One important thing is maintaining your cassette deck properly. The heads need to be scrupulously clean so you need a good supply of cotton buds and IPA. It also helps to demagnetise them from time to time using a wand type demagnetiser. Many decks that you buy will require the belts replacing otherwise you may find the speed goes slightly wayward. I have a queue of decks that I'm working on right now with this problem.

I'm now a convert to using a Nakamichi deck for transfers. I used to use Aiwas which were OK but the Nakamichi that I'm currently using seems to give a much better sound.

There are probably a few other things I've missed but it is time to join the party...
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Re: Digitising Cassettes

Postby James Perrett » Wed Apr 08, 2020 11:18 pm

Just coming back to this - on the subject of noise reduction...

There are two types of noise reduction usually involved in cassette transfers - noise reduction encoded on the tape and single ended digital noise reduction that can be applied to any tape. It is best to transfer the tape flat with no noise reduction on the playback machine. You can then use something like Izotope RX or Adobe Audition to reduce the tape hiss by selecting a short section with noise but no audio and using that as a noise print for the noise reduction software. These work best with a constant noise level which is why it should be the first process to be done. Don't try to do too much at once - if the noise level is high then it is usually better to do a couple of passes with 10dB reduction rather than a single pass with 20dB reduction.

You can then decode any double ended noise reduction afterwards if needed. This is because Dolby B (the most commonly used system) is fairly particular about levels and the high frequencies on the tapes often seem to self erase a little over time so Dolby B tends to reduce the high frequencies too much. However, undecoded Dolby B sounds too wispy to me so I usually use Uhe's Satin tape emulator which includes encoding and decoding for various noise reductions systems. I play around with the input level on Satin to obtain the best match while listening to things like ride cymbals.
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Re: Digitising Cassettes

Postby Tim Gillett » Thu Apr 09, 2020 12:00 am

James Perrett wrote:Just coming back to this - on the subject of noise reduction...

It is best to transfer the tape flat with no noise reduction on the playback machine. You can then use something like Izotope RX or Adobe Audition to reduce the tape hiss by selecting a short section with noise but no audio and using that as a noise print for the noise reduction software. These work best with a constant noise level which is why it should be the first process to be done. Don't try to do too much at once - if the noise level is high then it is usually better to do a couple of passes with 10dB reduction rather than a single pass with 20dB reduction. For it destroys the unity gain.

You can then decode any double ended noise reduction afterwards if needed...

Dolby B,C,S require "unity gain" from the output of the Dolby encoder to the input of the Dolby decoder.

Successful decoding of Dolby B let alone C cassette tapes can be difficult enough, if sometimes impossible, but applying digital noise reduction prior to attempting decoding all but rules out any hope of a successful Dolby decode.

If single ended denoising must be used, use it after having successfully decoded Dolby, not before.
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Re: Digitising Cassettes

Postby James Perrett » Thu Apr 09, 2020 12:31 am

Tim, when I do single ended noise reduction I take great care to not change the spectral balance of the wanted audio. If the spectral balance changes then I've gone too far with the noise reduction. I don't use Dolby decoding to reduce noise (that's just a by-product as far as I'm concerned) but I use it to restore low level high frequency signals back to their correct levels.

If you decode the Dolby first you end up with a varying level of tape hiss (aka noise modulation). You also cannot obtain a sensible noise print as the Dolby will reduce the level of the noise when everything is quiet but leave the noise when audio is loud. To do effective digital noise reduction you need a constant level of noise.

Of course, you may work in a different way - this is just what works for me.
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Re: Digitising Cassettes

Postby Tim Gillett » Thu Apr 09, 2020 2:06 am

James Perrett wrote:Tim, when I do single ended noise reduction I take great care to not change the spectral balance of the wanted audio. If the spectral balance changes then I've gone too far with the noise reduction. I don't use Dolby decoding to reduce noise (that's just a by-product as far as I'm concerned) but I use it to restore low level high frequency signals back to their correct levels.

Firstly, the tape noise was already "reduced" at the record stage when the encoder boosted the relevant programme up to 10 db above the anticipated tape noise. We get that noise reduction whether we like it or not. In spite of its problems, that is the beauty of "double ended noise reduction", and it will always put "after the fact" single ended NR in the shade. It's not single ended NR's fault. It simply doesn't have the information to work with. But that's perhaps another discussion.

So we cant disentangle the wanted and unwanted. We cant tell the decoder "I plan to do the denoising part later" or " I will help you by reducing the noise that you don't need anyway". It doesn't work like that. We must present all the data for the decoder to successfully decode. There must be "unity gain", including flat frequency response, between the encoder's output and the decoder's input. Admittedly often a tough call for a cassette.

James Perrett wrote:If you decode the Dolby first you end up with a varying level of tape hiss (aka noise modulation).

On a given programme after successful decoding, there's a whole load of modulation of the tape noise, usually moment by moment, except in steady, quiet moments of the original performance. But Ray Dolby designed it so the programme masks the changing tape noise. We don't hear it. And, perhaps neither does any Denoiser used post a successful decoding "hear" the tape noise modulating.

If we are hearing noise pumping or dynamic changes to the programme, it's not decoding properly.
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Re: Digitising Cassettes

Postby ef37a » Thu Apr 09, 2020 8:09 am

Re "mechanisms". Some months ago I scored 3 5 packs of TDK SA 90 from the Scope shop in town. Back home I settled down to copy some PC audio to cassette (for the jam jar). Machine is an excellent Sony Dolby S deck.

All seemed well on playback until about 20 minutes into the tape when the most appalling wow and flutter began and got steadily worse, like the music was under water. I examined the tape and it seemed be 'concave' and shiny not flat and matte.

Over the next few days I worked my way through all but one of the 15 tapes and all had the fault (on a second machine to boot)...SO! I have a batch of one of the best ferric cassettes ever made in my view that are bloody useless! The tapes run, wind and rewind as I would expect with minimal noise so I think the mechs' are in good order.

If anybody wants a few for transplants. pop me a PM and I shall jiffy them to you.
BTW the packs were marked at ONE POUND each! And no, I did NOT accept the change from my fiver! I would have been happy to pay a fiver a pack but now of course would be even more hissed off.

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Re: Digitising Cassettes

Postby ef37a » Thu Apr 09, 2020 8:19 am

Just to say, it seems OP has some sort of interface for the digitizing?

I would like to suggest to any absolute newb that maybe does not want to get too deeply into the matter and wants to keep costs low, buy a Behringer UCA 202 (222?) .

This little box will accept RCA phono plugs which virtually all tape decks and hi fi systems use and the audio quality is quite good enough for tape dubbing (ok, not master tapes of 'classicals' !) The noise floor will be around 80dBfs and the replay quality close to the best CD and way better than most internal PC cards.

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Re: Digitising Cassettes

Postby Mike Stranks » Thu Apr 09, 2020 8:42 am

Good stuff here...

... a cautionary note on head demagnetisers. If you don't know the correct way to use one you can end up doing more harm than good. If in doubt, ask the boffins here... people who REALLY know what they're talking about have already contributed excellent 'how to' advice.
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Re: Digitising Cassettes

Postby ef37a » Thu Apr 09, 2020 10:38 am

Mike Stranks wrote:Good stuff here...

... a cautionary note on head demagnetisers. If you don't know the correct way to use one you can end up doing more harm than good. If in doubt, ask the boffins here... people who REALLY know what they're talking about have already contributed excellent 'how to' advice.

Good point about de-maggers Mike. In all my years using and fixing cassette machines I have never known one suffer noise due to magged up heads and since the vast majority use a common rec/replay *head it has AC bias running though it from time to time. Even play only machines however, in cars an factory PA racks never seemed to have a problem.

Of course, if you are about to play a very high quality tape, especially of a rare and valuable recording, take all proper care but even then, if you don't use the wand properly as you say Mike, the deck will be in a worse state than before!

*Bit of advice. If you have a cassette deck that is only used for replay purposes it is a good idea to put it into record mode a few times a year. This is because the rec/play switch contacts can become tarnished and cause all kind of weird problems such as no sound to screaming instability. A few shunts back and forth and the switch self cleans. Some decks use relays and these suffer the same fate. The Hitachi VHS machines did as well.

Dave.
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Re: Digitising Cassettes

Postby Hugh Robjohns » Thu Apr 09, 2020 10:43 am

Tim, I'm not sure you're actually reading what James is explaining.... but his process sequencing seems entirely valid and appropriate to me. It's how I would do it too, and the necessity for unity-gain with the Dolby decoding is taken care of by adjusting the input level to the decoder, as James described -- something that is typically needed anyway when playing a tape back on a different machine to the one it was recorded on because of notoriously unreliable stock alignments.

The aim is to reduce tape noise further than the capabilities of Dolby on its own, while maintaining an accurate reproduction frequency response from the Dolby decoder.
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