Pre recorded cassette tape degradation

[stevehertz]

I have obtained an original, pre recorded cassette of Steely Dan's Pretzel Logic. I have reason to believe that the sound is 'dull' compared to when it was new. There's no problem with my cassette deck which is azimuth checked and set and well maintained. Machine set to ferro and Dolby B selected as is appropriate. I have the album on CD so I could easily make a copy onto a better type II tape and no doubt it would be better. Saying that, it would be nice for nostalgia reasons to retain the original cassette with its original labels etc.

My question is, is the degradation due to the tape itself degrading, or the recording degrading? Obviously I have no knowledge how it has been stored in the past (heat etc). What factors cause degradation of the tape and what factors result in the actual recording being damaged? And are there any factors that affect both eg heat? I presume an AC field affects the recording but not the tape itself.

I'm thinking about re recording from CD on to the original ferro tape. But if the tape itself has degraded there's little point. Like I say if all else fails I can make a new type II copy, at least it will be housed in the original case.

[cmjones01]

In my experience, it's very likely that even if your cassette deck is set to the 'correct' azimuth, it still doesn't match the tape. To get the best results from cassette playback it's generally necessary to set the azimuth on playback for every tape, if it wasn't recorded on the same machine. Playback with Dolby B generally makes this problem worse: both the frequency response and absolute level are critical to get Dolby to work properly. Anything that doesn't quite match the recorder ('correct' adjustment of the player doesn't help, since every recording has some error) will result in a muddy, dull sound, or treble that pumps obviously in and out.

I haven't found old cassette recordings to deteriorate, in general, though print-through can be a problem. I've recovered good, crisp audio from some communist-era pre-recorded cassettes here in Poland simply by adjusting the playback deck to suit them. The tapes themselves are of terrible quality (the oxide tends to fall off, leaving awful dropouts, and the background noise level is high) but the underlying recording is good, and still sounds good after 35 years of storage.

Chris

[jez_145]

Another possibility is that, especially if the tape has been played a lot, the top end performance may be affected by the playback head being partially magnetized. In professional tape recording situations, tape heads were regularly demagnetized for this very reason. I doubt that many pre-recorded compact cassette owners followed this procedure.

Jerry

[stevehertz]

Good points guys, thanks.

Chris, adjusting the azimuth for playing back each different pre-recorded cassette is clearly not a practical solution - unless you have a deck with user azimuth control. I set up my decks using a lissajous figure at 8 or 10khz. So you can't get much better than that. But as you alude to, that's assuming the test cassette was made at 100% accuracy. No, the world of cassette player azimuth accuracy is not an easy one to get right.

[paulsherwin]

I agree with Chris. While cassettes don't generally degrade, the quality of commercial releases varied a huge amount, particularly before the arrival of HX-Pro equipped duplicators in the 90s. Dolby tracking problems were very, very common and this tends to make the recordings sound dull unless Dolby processing is switched off.

Of course, old tapes can degrade because of poor handling and storage - playing on lousy or faulty players, being left in the sun on car dashboards, stored for years in damp garages etc. There can also be print through problems.

[wd40addict]

You need one of these

https://en.wikipedia.org/wiki/Nakamichi_Dragon

[TIMTAPE]

I've transferred (digitised) tapes and discs for many years as part of my work. I wouldnt be without a front panel Azimuth Adjuster control. Very few stock cassette decks had them so if it looks like it's possible on a particular deck, I custom modify the deck to accept the adjuster. The photo is of one I made for a Nakamichi 480 deck.

For the very best treble response, tape to head gap contact needs to be intimate. On a head so worn that it has a tape shaped slot worn in it, adjusting azimuth may not be a good idea. Rotating the head rotates the slot which forces the tape to travel in a zig zag path which it normally doesnt appreciate. Sometimes the tape lifts out of the head gap and the sound becomes even worse than before adjustment. Ideally the adjustment is only performed on a head with no wear and so no slot or ridges.

As mentioned, getting Dolby B to track accurately can be difficult if not impossible. Many factors can conspire to alter the signal level especially in the highs. Azimuth error, poor tape to head contact, mild demagnetisation as Paul mentioned, especially with the Type I (normal formulations), and even a cassette recording that was never calibrated in the first place, such as from a high speed tape duplicator whose record head was overbiased.

Dolby B encoding and decoding was designed to respond to the high frequencies right up to 20 kHz. That's very ambitious for cassettes. If the programme material carried frequencies out to 20 kHz, and they triggered the encoder, then those same frequencies need to be available in playback, and at exactly the same level relationship, in order to be "decoded". That's a tough assignment.

Interestingly years later when Ray Dolby brought out Dolby C, he revised the settings so that the encoding and decoding process now only extended up to 10 kHz. Above 10 kHz there was no noise reduction at all. A smart move as the process was now less sensitive to small errors. Also human hearing is less sensitive to frequencies above 10 kHz including tape hiss.
In the 90's we recorded talking book tape masters with Dolby B encoding but limited the recorded highs to a max of 10 kHz for less decoding errors.

I've tried to restore Dolby tracking on cassette recordings which were the only remaining copy of a valued recording. Sometimes it's been a reasonable success, other times not. When the tape has diminished highs I selectively boost them to try and restore the flat response which Dolby decoding relies upon. But the boosting must be done pre the decoder and it requires some educated guesswork and an ear to "hear" the particular Dolby artefacts and just as important to "hear" when they have been removed or removed as well as possible.

Many later pre recorded cassettes especially from the big record companies were quite well recorded. Many used Chrome or Pseudo Chrome tape (it's often stated on the case) which had the advantage of being less vulnerable to partial erasure of the highs due to repeated playing with magnetised heads. They also often carried a very brief test signal on all four tracks (stereo sides A and B). It can be used to check the frequency response of the playback. Usually the tone set extends to 20 kHz but in my experience, achieving flat response to 16 kHz is more realistic. But the signals are so brief that the only way to make use of them is to digitise the recording and then inspect the tones visually on a computer screen.

[TIMTAPE]

Originally Posted by wd40addict

You need one of these

https://en.wikipedia.org/wiki/Nakamichi_Dragon

The Dragon's auto azimuth system did the best it could with the limited information. It only used the right channel so if there were poor highs there but good highs on the left channel it was lost. It also had to be very damped in its response as it was trying to do the equivalent of tuning into an AM radio station not knowing what was the broadcast frequency. It had to constantly hunt, but slowly and couldnt respond to abrupt azimuth changes such as when two recordings made on machines with different recorded azimuths butted up against one another.

A useful feature for decoding Dolby tapes is the "play trim" control on some Yamaha and NAD cassette decks. It allows you to boost the playback highs pre the Dolby decoder. On some tapes it's enough to restore Dolby tracking but of course everything else in the chain has to be pretty much optimised as well.

Ah, Dolby and cassettes. Mostly not a happy marriage.

[Ted Kendall]

Several points here. Firstly, cassettes were duplicated at anything up to 64x play speed, and getting consistently good results on such plant was akin to balancing a cone on its point. I have an edtion of Sounds Good from around 1976 in which Angus McKenzie demonstrates some of the samples of pre-recorded cassettes used in a Hi Fi News group test, and the spread of quality has to be heard to be believed. The records companies tended to use the cheapest tape stock they could find, saving something like 3p per unit on cost. A similar policy applied to shells - frequently the pressure pad was a simple block of foam, similar to that used on 8-track cartridges, instead of the usual sprung felt pad.

Dolby B does require fairly close alignment to avoid top loss on replay, and azimuth is pretty critical here. Unfortunately, it is quite possible, even on decent machines, to get a substantial shift in azimuth simply by ejecting and replacing the cassette. Dual capstan transports reduce this problem considerably, as the tape path across the head is isolated from the vagaries of the cassette shell. Lifting the pressure pad, as Nakamichi did on dual-capstan transports, removes another random variable.

Close control of bias is also critical to correct top response, and the spread in practice was wider than desirable. It was probably this which led NAD to put a variable HF control (play trim) on some decks, in oreder to improve Dolby tracking.

The master from which the cassette was duplicated would be to some extent doctored to get the best results from the copies - perhaps some peak limiting and top lift to offset losses in the duplication process.

The question of whether cassette tapes fade at the top end has been discussed among archivists for twenty years at least, and the best answer we can up with as yet is "definitely maybe". Magnetised playbaclk heads are a sure way of wiping top off, as is coating deterioration, but simple loss as a result of age is less certain. I recently dug out some casettes I made in the
early 1980s, to test a machine I had overhauled, and they sounded pretty much as I remember. but these were TDK stock recorded on a decent machine from a good source.

In short, although a real-time copy of a CD can sound remarkably close to the original, it is very much a matter of luck whether a commercial pre-recorded cassette will stand up to even half-critical listening.

[paulsherwin]

I also have some recordings made in mid to late 70s which don't appear to have deteriorated at all, at least subjectively. These were made on TDK and Maxell stock using mid market hifi equipment of the day. They used Dolby B, and the tracking appears to still be correct.

My own recordings always sounded better than all but the very best commercial cassettes.

[TIMTAPE]

Originally Posted by Ted Kendall

...In short, although a real-time copy of a CD can sound remarkably close to the original, it is very much a matter of luck whether a commercial pre-recorded cassette will stand up to even half-critical listening.

I made some tests with a couple of pre recorded cassettes from a large record company, Polydor ( Chrome formulation and probably high speed duplicated) and with proper playback alignment on a good deck they played back pretty well, Dolby B decoded. The facility's own brief alignment tone set allowed a more objective correction of top errors. But in the end it was just a technical exercise to see what was possible. For why would anybody use a cassette copy when you have the original pro studio master tapes from which to remaster?

I dont think high speed duplicating in itself (recording ultrasonic frequencies) was the problem for if it had been, quality video recording would never have been possible. I suspect the problem was more with facilities which did not or could not maintain their duplicating gear to a high standard, not least replacement of worn record heads or at least as you say, care in calibrating record characteristics, which admittedly could be very tedious.

I should know. Our talking book duplicating room had a bank of about 20 cassette slave decks, each with 4 tracks to align. Record bias alone was 80 separate adjustments! And no playback head in the decks. Only the record head. I had to make separate recordings, play each recording back on a calibrated cassette deck, and eventually by trial and error arrive at the best bias levels, four for each slave unit. Very time consuming.
Fortunately the heads were all quality Ferrite types which generally lasted well, which they needed to, but eventually with such brutal high speed treatment 5 days a week they all needed replacement, with all the recalibration that involved.

I havent seen a proper high speed cassette duplicator now for many years. Some of the duplicator companies such as Graff (UK) modified their smaller high speed cassette duplicators into high speed cassette digitisers with only a playback deck fitted, feeding an AD converter. Good for fast digitising of many cassettes but not quite pro standard.

[Ted Kendall]

Originally Posted by TIMTAPE

I dont think high speed duplicating in itself (recording ultrasonic frequencies) was the problem for if it had been, quality video recording would never have been possible.

The crucial point here is that video recording is FM, so noise, distortion, uneven frequency response and mechanical deficiencies have less effect on quality than with AM recording.
Flutter at x64 speed can resolve into distressing wow at baseband, but for my money the inherent bugbear was modulation noise, which gives a "papery" quality to reproduction and is present to a greater or lesser degree on every high speed duplicated issue I have heard, be it cassette or open reel. It was with some surprise that I learned that even the EMI Stereosonic tapes were mostly duplicated at x2, and bias analysis confirms this/

[stevehertz]

I re-recorded on to the original ferro tape from CD using Dolby B. The audible results were still rather poor. Not to mention the poor mechanical aspects of the cheap Ferro cassette. I then made the same recording on to a Maxell UDXL II and the difference was light and day, better highs and no audible wow as was occasionally apparent on the old tape. I don't think I'll bother trying to get good quality recordings on to any pre-recorded tapes as both their mechanical quality and tape tape quality just don't warrant it. It was just a nice thought in order to keep the original format, labels, vibe etc; nostalgia.

Thanks for the informative and interesting input guys.

So, I'm assuming that Dolby C is the best choice to record with if the machine has it?

[emeritus]

The very worst example of cassette tape shedding I have experienced is a commercial cassette of "The Shadows Greatest Hits". Shedding is so bad that the sound gets unacceptably muffled after the third or fourth track and would mask any high frequency loss. Fortunately I have the same album on vinyl. I have had negligible shedding on blank cassettes, even cheap ones.

[Ted Kendall]

Originally Posted by stevehertz

So, I'm assuming that Dolby C is the best choice to record with if the machine has it?

I was never that impressed with Dolby C - whenever I tried it I could hear odd level changes even when playing back on the same machne which made the recording. Dolby B was far less fussy.

[paulsherwin]

I agree with Ted. If you use C there will be lots of kit that can't decode it properly anyway. I routinely used B back in the day, but there's a lot to be said for not using noise reduction at all with good quality high output tape stock. You get a bit more background hiss, but there are no companding artefacts or tracking problems.

When Dolby B was being designed in the early 70s, most cassette tape stock was pretty grim. TDK and Maxell revolutionised the market.

[stacman]

Agree with Paul an Ted here, Paul on the recording’s made by myself were superior to most bought pre recorded cassettes, if made on decent tapes,
Also with Ted re the Dolby issue, never impressed with dolby recording, too much mis-tracking,
Youtube has Tony of ‘Cassette Comeback’, who does great videos on the cassette media,

Emeritus.....was that The Sheddows greatest hits’.....
Regards, Alan

[Nickthedentist]

Same story with VHS.

Own recordings, assuming the machine is in good condition and not an absolute cheapie, were always good, and in many cases, barely distinguishable from an off-air broadcast.

Pre-recorded tapes varied from excellent, to barely watchable. Most were somewhere in between.

Nick

[Ted Kendall]

The problems of mass video duplication were more those of machine maintenance and quality control, as copying was done at baseband. As ever, economic pressures frequently caused less care to be taken than should have been. The problem that caused me most annoyance seemed to be misalignment of head switching points on the hi fi soundtrack, causing that maddening subdued clatter.

[TIMTAPE]

Originally Posted by Ted Kendall

The crucial point here is that video recording is FM, so noise, distortion, uneven frequency response and mechanical deficiencies have less effect on quality than with AM recording.
Flutter at x64 speed can resolve into distressing wow at baseband, but for my money the inherent bugbear was modulation noise, which gives a "papery" quality to reproduction and is present to a greater or lesser degree on every high speed duplicated issue I have heard, be it cassette or open reel. It was with some surprise that I learned that even the EMI Stereosonic tapes were mostly duplicated at x2, and bias analysis confirms this/

Earlier pre recorded cassettes often seemed of indifferent quality but the ones I mean were later ones made when CDs were starting to compete with pre recorded cassettes for market share. The larger duplication facilities upped their game with better shells and Type II tape. Often these cassettes were distinguishable by clear shells and white text printed directly onto the cassette itself. No paper label. Another reason a home cassette recording may have sounded more HiFi could be if it was recorded and played back on the same deck. No azimuth error! But was the same cassette deck aligned to the pre recorded cassette's azimuth pattern? These later PR cassettes were also recorded not "in cassette" but on open reels of cassette width on often Studer pro machines specially modified for the task. These were also true 3 head machines so easy to align on all 4 tracks although the frequencies reached well into the RF band of course. Being recorded as open reels, no pressure pad and very stable tape tracking, more so than in a shell. These later pre recorded tapes therefore often were a good stable reference tape for azimuth. I have a feeling even quality cassette alignment tapes were also made at high speed. Re modulation noise on these later cassettes high speed duplicated by the big companies I can't say I've ever noticed it. Pro duplicators, even our more humble Otari " in cassette" types tended to have no erase heads, further reducing noise. I must check to see if I kept a digitised example of such a later pre recorded cassette.