How long should cassettes actually play for?

[Nickthedentist]

Hi everyone,

I've been messing around with a few old cassette decks recently, in part to digitise some old tapes which I'd like to listen to on my phone while out and about.

I've set the speed using a home-made, A = 440Hz test tape which I made many years ago using a brand new Tascam 122 deck which the school I attended had just purchased.

But every cassette I've transcribed to Audacity seems to last about 1 minute per side longer than claimed, e.g. 46 mins for one side of a C90.

Is this normal? Or was the brand new Tascam (and hence my decks) running slow?

[knobtwiddler]

I'll start this with the caveat that my brain just gave out a cloud of dust, considering it's such a long time since I made cassettes, but I remember that they always gave you an extra minute or so's grace period. Even if your deck is quartz-locked and uber-accurate, I think you'll find 46 minutes is typical.

[paulsherwin]

This is normal. Blanks are usually a bit longer than the nominal length, perhaps to stop owners of fast-running equipment complaining.

[Nickthedentist]

Thanks, both, that's reassuring.

I had a feeling that was the case, but I couldn't find anything to back it up online.

Nick.

[paulsherwin]

It may derive from the original Philips decision to market cassettes defined in 'minutes' rather than by physical length in metres or feet.

[ricard]

Anyone remember those "C90+6" cassettes that Agfa or BASF marketed once, I think in attempt to make it possible (or at least more likely) fit two LPs on a single side of the tape?

[wireman]

I'm sure TDK did an SA100.

I found this quite amusing: from the Q&A on an Amazon Maxell tape listing I just looked at:

Question: What colour is the tape, black or brown? The tapes that are black sound better.
Answer: I have always black tape smells better but brown tape tastes better.
By Saki on 12 April 2020

[Lucien Nunes]

It's a long time since I paid any attention but I recall C60 as 88m in length and C90 as 131m. At 4.75cm/sec these give 30'53" and 45'58" playing time per side respectively.

[TIMTAPE]

The slightly extra length may also relate to production tolerances. Perhaps the cassette winding/loading machines couldnt wind exactly 45 minutes of tape per side so they dialled in say 46 minutes, guaranteeing a worst case minimum length of 45 minutes, but an average of 46 minutes.

We recorded Talking Book masters for eventual duplication onto C90 cassettes, but even though we knew the average cassette ran to about 46 minutes per side we still recorded no more than a 44 minute programme per side, again because the tapes and machines werent perfectly accurate, and multiple inaccuracies could be additive.

Sometimes we had to duplicate material which, against our guidelines, had narration recorded onto every spare second of the tape. No blank run in or run out. With a slave running slightly faster than the master, words could be missed at the end of side 1 and the start of side 2. I standardised all the duplicator slaves to run at nominal cassette speed, but to build in a little extra safety margin for these "rogue" tapes, I set the master deck to run very slightly faster than standard speed to avoid missing words on the copies. The duplicator operators got used to the sound of the master tape coming to its end a little earlier than the multiple slave tapes, a reassuring sound. But of course some "C90" master cassettes ran even longer than say 46 minutes per side so the system wasnt foolproof.

[Takapuna]

One of the many variations of the last few Maxell UR90 knocking around at present states "Recording time 90min (2x45min) 135m/443ft on the outside of the index sheet. At 1.75ips I make this 47min 15sec. The five seconds of leader tape at each end might or might not be included! Makes a good speed check end-to-end if it can be trusted and you have the patience!

[ben]

Originally Posted by TIMTAPE

With a slave running slightly faster than the master, words could be missed at the end of side 1 and the start of side 2. .

This is of course the problem when duplicating A + B in one pass. If the copy is of different length than the master, you either get lost programme material or - also annoying - a long pause at the start of the second side (if a long enough delay is present after pushing Play, listener may erroneously assume the tape is blank!)

[TIMTAPE]

True. Our workaround for the blind listeners was a spoken message: "That is the end of side 1. After this message, please stop the tape and (without rewinding or fast forwarding) turn over the cassette to side 2. Please do this now." If they did this, and we'd recorded our masters properly, there was no delay.

This also applied to Library of Congress 4 track cassettes. Each side didnt have to be of exactly the same length but the beginning of a new side had to be level with the end of the previous side.

Recording the LOC format to 4 track to reel to reel master tapes was a little tricky. At the end of a "side" we had to "turn over" the two reels a total of three times mid tape, without displacing the tape in time, and trying not to touch or damage the exposed tape in the process. We did it by placing the one reel on top of the other, flipping them together, then separating them and replacing them on the spindles.

Speaking of tape length, the open reel tapes seemed always to be more generous with spare tape than the cassettes. A nominally 45 minute tape (1800 ft at 3/75ips) seemed to run in minutes to the high 40's if not into the low 50's.

[Craig Sawyers]

Lou Ottens, who invented the cassette during his long career at Philips died at the weekend at the ripe old age of 94.

https://www.bbc.co.uk/news/world-europe-56355444

[knobtwiddler]

This weekend, on a Sony Quartz deck, I am seeing 32.05 for a Maxell XLII C60 (92 date) - and 46.35 for a TDK SA90 (97-98 date).

Not quite Nobel-level research, I admit.

[cmjones01]

I remembered that 1970s BASF cassettes have the length marked on them. Here's the inlay card from a 60-minute one which clearly states 88m length. I seem to remember that 90-minute cassettes were 135m long but can't immediately find one to check.

Chris

[Refugee]

That is the length in metres surely.

[Richard_FM]

I remember some 1980s Children's talking books used to have the same material recorded on both sides of the tape, so listeners just needed to turn the tape over when they wanted to listen again.

I have one album of TV themes where the B side runs for a fair amount shorter than the A side, so I always had to remember to fast forward it to the end.

[broadgage]

Some cheaper cassette decks were locked to the mains frequency, another reason to allow a slight safety margin WRT to running time.

A "45 minute per side" tape if recorded with the mains at 50.5 cycles would only run for about 44.5 minutes which could result in complaints.
If on the other hand the tape had an actual running time of 46 minutes, then with high mains frequency it would still run for about 45.5 minutes.

A slightly greater margin would allow for overseas grid supplies, or generators that might vary from 49 cycles up to 51 cycles.

[ben]

The only cassette units I've seen with AC mains motors were Tandberg and Akai models, and they weren't cheap!

[Andrew2]

Originally Posted by ben

The only cassette units I've seen with AC mains motors were Tandberg and Akai models, and they weren't cheap!

My Sharp cassette deck of the mid 70's had a AC mains motor, and quite a big one at that. I'll see if I can find the model number.

Ah, here it is, it was an RT-2500, built like the mythical concrete out-house.