SOUND ON SOUND

[ef37a]

However, even today there is still no other convenient way to record an audio source such as a radio programme or TV sound.

Except for those of us who still have our minidisc recorders! :D

Oh! I 've got two of those and one is a Grundig FCS! One of those is being integrated into the digitizing "suite" I am building with the cassette machine and a DVD player. I also have a VHS machine but have not fired it up in yonks so have to see if it still works.

Dave.

[nathanscribe]

Wait, people still have radios and TVs? I thought teh kids just used their phones for everything now!

I prefer cassettes to CDs (and I dislike streaming as well).

[James Perrett]

Nakamichi thought it was wrong too - which is why they came up with this...

https://www.youtube.com/watch?v=VrFU9kQrvNk

I cannot see that helps the supposed problem much? Cassette tape can "pack" against one side of the case and cause wow and probably weaving over the heads and poor sound. Just flipping the cassette round won't fix that AFAICS.

Well it may have been a bit of a gimmick (I never noticed a problem with the auto reverse in the car) but I've just got hold of one of those decks and it works very well as a player - it just seems to sound more stable than the other decks I have here. I do have a Hitachi 3 head dual capstan machine that needs new belts but I think the Nakamichi, despite being only a single capastan machine, sounds better.

[ConcertinaChap]

Moreover, the self-erasure issue with cassettes tends to appear worse than it really is because of the almost ubiquitous use of Dolby B, such that a slight loss of HF from the tape is further reduced by the mistracking action of the Dolby B decoder.

There is a plus side here, in that cassettes I recorded in the late 70s and 80s with Dolby encoding sound quite reasonable now with the Dolby switched off. In other words the Dolby encoding is compensating for the HF loss. It's all very rough and ready and of course you lose your hiss reduction but what the heck. If it sounds OK after all this time you're not doing too badly.

CC

[ef37a]

Nakamichi thought it was wrong too - which is why they came up with this...

https://www.youtube.com/watch?v=VrFU9kQrvNk

I cannot see that helps the supposed problem much? Cassette tape can "pack" against one side of the case and cause wow and probably weaving over the heads and poor sound. Just flipping the cassette round won't fix that AFAICS.

Well it may have been a bit of a gimmick (I never noticed a problem with the auto reverse in the car) but I've just got hold of one of those decks and it works very well as a player - it just seems to sound more stable than the other decks I have here. I do have a Hitachi 3 head dual capstan machine that needs new belts but I think the Nakamichi, despite being only a single capastan machine, sounds better.

Aha! They HAD to flip the cassette because you need two capstans for auto-reverse!

But I doubt there would ever be a tape handling problem with a Nakamichi? REALLY well engineered.

Dave.

[Tim Gillett]

I really don't see why any tape format should lose HF over time unless exposed to a magnetic field?

It's entropy innit? The signal recorded onto the tape via the orientation of magnetic particles degrades as those particles gradually attempt to revert back to their non-oriented state.

This happens on all tape formats, but is generally worse for thinner, slower tapes, and higher magnetic flux levels. So use standard-play tapes rather than long play, higher tape speeds where possible (open-reel, not cassette, obviously), and don't thrash the record meters to force heavy saturation!

Although gradual self-erasure affects all frequencies, it is the higher frequencies that are affected most quickly and most obviously, although keeping the tape cool helps to minimise the problem for long-term archives. The magnetic field embedded within adjacent layers of tape can also advance the self-erasure process (as well as leading to pre/post echos in some cases).

Moreover, the self-erasure issue with cassettes tends to appear worse than it really is because of the almost ubiquitous use of Dolby B, such that a slight loss of HF from the tape is further reduced by the mistracking action of the Dolby B decoder.

I also reiterate my point? Unless the tape had reference tones recorded on it (as studio Dolby A tapes always should) how could you know the HF was down on 5 years ago?

The obvious answer is to compare the (cassette) tape with the source. I have often done exactly that in my previous career, and can state that self-erasure really isn't a myth... although it might not be quite the huge problem some would claim!

H

I'm not sure either way on tape self erasure. I understood that higher energy tapes were harder to erase just as they're harder to magnetise. So a Type II or Type IV tape would be less subject to accidental erasure than a Type I.

I also thought that multiple plays in a machine tended to gradually erase tapes hence the qualifier with calibration tapes to check them after a certain number of plays, not necessarily after a certain time. Also the need to properly demagnetise a tape machine to minimise the tendency to gradually erase tapes after multiple plays.

It's wavelength related too, only indirectly to frequency. So a loss of 3 db at 10kHz on a cassette would be equivalent on a pro reel to reel tape to a loss of 3 db at 80kHz which of course no one would notice.

I agree any serious test needs to be done with careful measurements. The thing with tape is that there are multiple causes for loss of the highs, not just self erasure. So , a tiny speck of dirt on a repro head, a worn or misaligned head, in various planes, can be enough to compromise the highs. It's often not appreciated that just playing a tape back at its optimum is not always easy.

Here's an example of a cassette recording (Maxell UDR Type I) I made off the TV in 1976. It's been played many times over the years but it seems to have survived reasonably well. Of course this cassette recording off TV cant hope to compete with the original BBC videotape's audio quality. The vision isn't my recording, only the audio.

https://youtu.be/KYFVx4gpe9c

[Rich Hanson]

With respect to auto-reverse sound quality, I found it depended on the system (albeit only two data points from me) - the system I had where there was a stereo head that was rotated when the tape was reversed was very much prone to mis-tracking. The other system was a four track head which was electronically switched when reversing direction. The latter was much more reliable.

I found this an interesting watch, too: https://www.youtube.com/watch?v=jVoSQP2yUYA

[ManFromGlass]

[ken long]

However, even today there is still no other convenient way to record an audio source such as a radio programme or TV sound.

Except for those of us who still have our minidisc recorders! :D

Aaaahh... but that's compressed audio, like MP3.

[Hugh Robjohns]

Aaaahh... but that's compressed audio, like MP3.

I much prefer the term 'data-reduced' as it allows far less room for misunderstandings. :D

But while MiniDisc does indeed use data-reduction, (called ATRAC) it's worth noting that it is actually a far more sophisticated and advanced form than MP3.

H

[ef37a]

However, even today there is still no other convenient way to record an audio source such as a radio programme or TV sound.

Except for those of us who still have our minidisc recorders! :D

Aaaahh... but that's compressed audio, like MP3.

Better than MP3 though I would aver? I have done (unscientific and v limited) test copying CD to MD and I could not tell a difference but I understand some music genres are more demanding than others? Choral work e.g? But as I said earlier, I would be quite happy for a MD to have the same playing time as LP but 16 bit linear. I understand the CD was originally going to be smaller and with less time? The "wives tale" is that the size was insisted upon to get the playing time and the odd sampling rate for much the same reason (the disc HAD to fit a Euro car slot?) I mean, why are they not 48kHz?

Butty but..Tape is NOT compressed?!! I have an AES journal article about a tape pre-distortion unit and it is said listening to what tape actually does to sound is horrendous!

Sorry Hugh, did not see your reply. I did not get the warning this time, have they scrapped the idea? Never stopped me making a (***) of meself anyway!

Dave.

[Wonks]

But while MiniDisc does indeed use data-reduction, (called ATRAC) it's worth noting that it is actually a far more sophisticated and advanced form than MP3.

It had the ability to block out all bagpipe, accordion and banjo sounds? Brilliant! :D

[Hugh Robjohns]

The "wives tale" is that the size was insisted upon to get the playing time and the odd sampling rate for much the same reason (the disc HAD to fit a Euro car slot?) I mean, why are they not 48kHz?

Last question first, The reasons CDs (and the standard for other commercial music) use a 44.1kHz sample rate is entirely due to Mr Sony having a warehouse full of NTSC U-matic recorders. Prior to Sony's development of the CD format early digital audio experimenters were generally working with bespoke hardware recorders of various types and sample rates of 50 or 60kHz.

Of course, it was clear that the sample rate had to be sufficient to allow a 20kHz bandwidth, which meant a rate of greater than 40kHz, but higher sample rates were increasingly difficult to generate so Mr Sony wanted to keep it as close to 40kHz as he could. It was also clear that 14 bit wordlength was the minimum for an acceptable dynamic range in a consumer product, with 16 bit as the target for professional applications (at that time that was the absolute state of the art).

Mr Sony could build A-D and D-A converters well enough (for the time), but the question was what to store all this audio data on for the CD mastering houses and production plants? The answer was those Umatic video recorders, and consequently the Sony PCM1600 (and later the 1610 and 1630) digital audio boxes digitised audio and made it look like a black and white video signal to be recorded and replayed on/off Umatic machines. (They also did the same with the F1 and later PCM701/601/501 consumer digital encoders using betamax.)



Being in Japan, the Umatic video recorders worked with a 30 frame, 525 line (B&W) video format. Not all of the video lines are available in a rotary-head video recorder because of the head-switching, and they settled on using 490 lines for the digital audio. It was also essential that whole audio samples are stored per line (rather than splitting them over adjacent lines), and with 16-bits per sample the video resolution allowed three samples per line plus some basic error protection coding.

So, do the maths: 3 samples per line x 490 usable lines per picture frame x 30 frames per second = 44100 samples per second!

And that's why we're stuck with 44.1kHz as the basic audio sample rate.

Amusingly, when Mr Sony went on to develop a European PAL (635 line/25 frame) version of the hardware, the ended up using the same 3 sample per line structure, but 588 active lines, so the sums are 3 x 588 x 25... which also equals 44.1 samples per second!

Later, when it came to sound on digital video recorders it became necessary to ensure a whole number of audio samples per video frame (to allow easy editing). Although 44.1 obviously works with 25 fps PAL and 30fps B&W NTSC, it doesn't work with 29.97 fps colour NTSC or 24fps film.

The next lowest available number that does work is 48kHz, which works perfectly with PAL, B&W NTSC and film. It still doesn't work with 29.97 colour NTSC but nothing practical will anyway... but there is an easy bodge where five frames of 29.97 hold a whole number of audio samples. So 48kHz became the standard sample rate for all things video.

It would have been so much better had the original CD audio sample rate been selected as 60kHz (which would work for all video formats in the same way as 48k does), as then we would have had no need for double (96k) rates etc.. but such is life!

As for the physical size of the CD, the limiting factor was a disc that would fit in a standard ISO-sized car hi-fi unit. The alleged requirement to accommodate sufficient play time for a Beethoven symphony was obvious, but probably secondary, and there was some wriggle room anyway in the choice of the linear rotational speed and data coding format!

H

[ef37a]

Thank you Hugh and I bet that all came out of your head!

I would love to know what politking went on to keep the MDisc out of car audio? The format is so obviously better suited having intrinsic protection. The vulnerability of the cassette has been touched upon and of course, despite great claims for it at the time, the CD will not put up with very much abuse.

MD sound quality is, as you say, very good if not quite 16bit linear but in a car?! The MD can also record double time and again the quality loss for ICE would not be an issue for the majority of people.

I recall the Great Four Channel Fiasco and I believe Philips would not relax the patent to allow 4 tracks one way? Had they done so maybe 4CH would have taken off and all those silly disc coding systems swept aside?

Dave.