deterioration of cassettes

The only problem with the Hitachi was that it didn't reject Radio Data signals very well - so I added a birdie filter before the decoder, which improved things considerably.

But if the general consesus is that most tuners have the 19kHz pilot tone present to a significant degree in the output, then most tuners are poorly designed from this POV - as Alofoz is suggesting. It really shouldn't be there.

Couldn't agree more. When I made my tuner, FM was new in this country (c. 1978). I knew there would be a problem with Dolby recordings from FM. IMO the problem existed in the FM system & that's where it should have been solved. Later, when I was shopping for a new tuner I put considerable effort into finding a tuner that did solve the problem. Naturally, salesmen had no idea what I was talking about when I asked about pilot tone rejection, even less idea that it could affect dolby recordings. In the end I gave up & added my own notch filters.

Thanks everyone for the interest.   A couple of specific responses.

Another possibility is that there is no deterioration, but you are hearing the bass-buildup that is endemic to cassettes.

At least on some cassettes, I thought I'd heard a boominess but wasn't sure if it was in the original broadcast.  I can't imagine how this could occur -- is there a physical explanation?   I had dimissed it as being the result of the fact that I used various types of tape ("normal" "chrome" etc) and usually remembered to select the right bias setting  and turn the Dolby on, but not every time.  (I never imagined I'd hang onto these tapes for so long).

Thanks, AV_guy, for the suggestions.  

Also, FWIW, I see the spike at 19 kHz when recording from FM to AA, but does not appear in when recording from the tape deck.

Andy

Andy,

You're welcome! Anytime! I too have an aging cassette library and it is hard to believe that I have had them for so long and they are still in fairly decent shape. The oldest one I have dates to 1976 when I got my first tape recorder.

At least on some cassettes, I thought I'd heard a boominess but wasn't sure if it was in the original broadcast.  I can't imagine how this could occur -- is there a physical explanation?   I had dimissed it as being the result of the fact that I used various types of tape ("normal" "chrome" etc) and usually remembered to select the right bias setting  and turn the Dolby on, but not every time.  (I never imagined I'd hang onto these tapes for so long).

I think that Jester700 gave you the clues here - the HF fall-off effect gets worse gradually, the higher the frequency. This would generally have the effect of leaving progressively less treble. The other thing is that your ears are notoriously fickle devices - we are accustomed to hearing a rather clearer sound in general these days, and a lot of cassettes that we thought were fine years ago suddenly don't sound relatively as good...

Another problem related to this is self-erasure. Because tapes store magnetised particles that are in intimate contact with each other between layers, it's quite natural for these layers to demagnetise each other. This is why, in general, you will get better results from shorter tapes, rather than C120s, because the tape backing layer is thicker, increasing the distance between the layers. We are talking about a sensitive surface layer, and a very long time for this to happen - and this will also gradually reduce the HF content.

Another thing to note is that if they are really old recordings and haven't been played for a while, then it's an excellent idea to spool right through them and back again before playing them at all. This frees up the pancake lubrication, and also reduces print-through effects, so that when you actually play them, you generally have less trouble.

"Bass buildup" is a fact of life with cassettes, particularly with those that have been used in multitrack portastudios. With each generation of track bouncing the bass frequencies are magnified, due to the inherent nonlinearities of the medium. You will find this happens with cassette dubs of CDs or (even worse) other cassettes. Back in the day I had a less-than-state-of-the-art playback system (and this was before subwoofers, I might add) and my stepson HATED the tapes I sent him because they were all boomy sounding on his system, while I blithely ignored the whole problem out of the inability to distinguish the lower notes on my playback setup. Now that I have a sub (and a much better stereo in every way) those old tapes are unlistenable due to the low frequency content. Naturally, now I burn CDs, and that problem has gone away.

it's an excellent idea to spool right through them and back again before playing them at all. This frees up the pancake lubrication, and also reduces print-through effects, so that when you actually play them, you generally have less trouble.

my ignorance:

How would spooling (you mean FF/rewind, right?) reduce print-through effects?  

Somewhere I picked up the idea that you shouldn't store a tape after doing so, as it winds the tape more tightly and increases print-through during the subsequent storage; and that rather, you should play it through at normal playback tension before putting it away.  This makes some sense to me, although dragging a precious tape once more across the tapeheads seems to be a drawback.  

But are you saying that spooling can somehow partly undo accumulated  print-through?

"Bass buildup" is a fact of life with cassettes, particularly with those that have been used in multitrack portastudios. With each generation of track bouncing the bass frequencies are magnified, due to the inherent nonlinearities of the medium.

I think that you are looking at this from the wrong end, even though the effects are the same as you describe, obviously. The medium's nonlinearity doesn't affect its bass frequency response like this at all. In relative terms, its the loss of HF which causes the problem - all that's left is the bass. The buildup in multitrack cassettes that were bounced was simply down to a sloping response at HF that rapidly built up on multiple passes. The absolute level of the bass doesn't increase - it's the level of everything else that decreases - this has been well documented for years! You think you've got more boom, and you have - but this is because you had to crank up the overall volume level to hear the HF parts of the track. The other factor in this, which inevitably exacerbates the situation, is that it really doesn't take too much over-bias to cause the recorded response to tip down at HF - and auto-erasure and tape compression takes place - but not to the bass, which is recorded much deeper into the oxide layer. So inevitably, even the first replay of cassettes made on over-biassed machines sounds bass-heavy anyway. The only advantage of this is that the distortion level reduces - so you get a nice high quality boom!

Another factor which also makes the situation worse is that most cassette recorders use their record heads for playback, and this is the one thing that they're not optimised to do. The relatively wide gap in the record head means that the extinction frequency (the wavelength which corresponds to the lowest frequency that will entirely fill the gap with an entire cycle of itself, therefore cancelling out) is much lower than it would be on a properly designed playback head, and therefore the frequency at which the head output falls significantly is much lower. That's why 3-head machines were always better - they had heads optimised for the functions that they were carrying out.

How would spooling (you mean FF/rewind, right?) reduce print-through effects?  

Somewhere I picked up the idea that you shouldn't store a tape after doing so, as it winds the tape more tightly and increases print-through during the subsequent storage; and that rather, you should play it through at normal playback tension before putting it away.  This makes some sense to me, although dragging a precious tape once more across the tapeheads seems to be a drawback.  

But are you saying that spooling can somehow partly undo accumulated  print-through?

Yes - there are a number of commonly held misconceptions about this. But don't take my word for it - read what 3M, endorsed by the AES have to say about it at the bottom of page 1 in this pdf document. They haven't told the whole story though. Print through is also temperature dependant, and once its reached its peak value, it won't increase beyond this.

The tape winding thing is dubious - there are plusses and minuses to the whole thing. Generally the method that's used for archive storage is to leave the tape tails-out. Contrary to what you are saying, this leaves the tape much more tightly pressed together than a wind or rewind ever will - but the speed at which the layers are pulled apart when rewinding appears to be the key to the reduction in print-through level in practical terms, although exactly why this works so well is a bit of a mystery, and hasn't been fully researched. A site that actually tells you what you can achieve by multiple wind passes has a reference to this  here - you have to scroll down to the 'questions and answers' part of the page for the information. I will tell you for nothing that the whole effect is actually counter-intuitive - which is why it seems to confuse so many people!

What seems more interesting to me is similar signals on LPs. I don't find them on most LPs, but see them every once in awhile. I spend most of the time in Spectral View, so it is obvious when it is there.

What I see is a horizontal line, not very bright but impossible to miss. It is generally about the same width as the 19kHz signal in the FM recordings (looks about 50Hz to me), but occurs at different frequencies from about 16kHz to 21kHz.

 

I used to hear these tones on some records from the 80's - especially when using an old Decca cartridge which probably had excessive high frequency resonances. I put this down to the use of early computer monitors in the studio which weren't adequately shielded. I would guess that most of the engineers involved couldn't hear low level tones at 15 or 16 kHz so they got through unnoticed. Most cartridges wouldn't reproduce these frequencies very well so very few people noticed.

I seem to remember some of Trevor Horn's work had these tones - possibly Art of Noise or something like that.

Cheers.

James.

Thanks for the links, Steve.  Fascinating phenomenon.

Generally the method that's used for archive storage is to leave the tape tails-out.

Once again I must ask for clarification.   This refers to open reels, I presume, with which I have no experience.  Is "tails out" the state after the tape has been played through, without being rewound?  

In the world of cassettes, where you flip the tape to access side B, can I translate this to ?
"In order to try to reduce any accumulated print-through:
a) whichever side of the cassette you are about to play, rewind it first;
b) play (don't rewind) the tape to the end of a side before storing it"

Andy

Once again I must ask for clarification.   This refers to open reels, I presume, with which I have no experience.  Is "tails out" the state after the tape has been played through, without being rewound?

Yes - but with a cassette you are stuffed if you've got things on both sides - usually the best result comes from spooling backwards and forwards a couple of times, so:

In the world of cassettes, where you flip the tape to access side B, can I translate this to ?
"In order to try to reduce any accumulated print-through:
a) whichever side of the cassette you are about to play, rewind it first;
b) play (don't rewind) the tape to the end of a side before storing it"

Andy

Pretty much, yes. But you might want to wind it more than once before playing it. Oh, and a silly little thing; make sure that the pressure pad is still glued on to the rear of the head channel on your cassettes. It causes very poor replay when it comes off!

"..make sure that the pressure pad is still glued on to the rear of the head channel on your cassettes. It causes very poor replay when it comes off!"

ABSOLUTELY! I ran into this problem many a time with my aged cassette library. Also if you can still find them Radio Shack used to sell a casette repair kit. This was an empty shell with leader tape and all the other parts to make a tape playable. I think they discontinued making these, but you might get lucky as I did and find a store that hsa some old stock. These kits were a valuable thing to have especially when the pressure pad was totally missing!

Oh, and a silly little thing; make sure that the pressure pad is still glued on to the rear of the head channel on your cassettes. It causes very poor replay when it comes off!

...and if you ever get into the murky world of transferring 8-track cartridges I defy you to find one where the backing pads haven't turned to sludge and need to be replaced. Fortunately those foam strips you can buy in rolls as sticky draft excluders are just the right width and thickness and serve as perfect substitutes!

(I sometimes worry about the largely useless information that's floating around inside my skull... )

I sometimes worry about the largely useless information that's floating around inside my skull...  )

It's that bit between largely and completely that makes the difference and is called experience.

I have a few 8 Tracks lying around that I need to transfer. I'll keep that in mind, but I think they are in good playing shape. Now the only thing is to dig out my old stereo to play them back on IF it still works...