Historical Development of Magnetic Recording

[DMcMahon]

Very interesting document.

[Ted Kendall]

A detail it doesn't mention is that before the serendipitous re-discovery of AC bias, there was an attempt to improve the dynamic range of DC bias by recording two parallel tracks on the tape, one modulated 10dB higher than the other. Suitable level-dependent switching would allow increased dynamic range to be reproduced. AC bias rendered such complication unnecessary, but the heads were of the configuration we would recognise as stacked stereo. RRG engineer Helmut Krueger used these around 1943 to construct a stereo Magnetophon, a few of whose recordings survive, and remarkably good they are, too.

3M re-developed the dual-track idea in the 1960s (their first use of the term "Dynarange"), but this time it was rendered incommercial by the advent of Dolby A.

[Outrun_uk]

Tim Hunkin’s Secret Life Of Machines - The Video Recorder episode is worth a watch, covers some of the history behind tape recording and a great practical demonstration of home made tape.

[TIMTAPE]

Originally Posted by Ted Kendall

...3M re-developed the dual-track idea in the 1960s (their first use of the term "Dynarange"), but this time it was rendered incommercial by the advent of Dolby A.

From memory 3M called it "Dynatrack".

[Ted Kendall]

Indeed, Dynatrack. The Isoloop transport remained 3M's standard kit thereafter, and a left-hand copy appeared in the Technics RS1500 series.

[barrymagrec]

Originally Posted by Ted Kendall

Indeed, Dynatrack. The Isoloop transport remained 3M's standard kit thereafter, and a left-hand copy appeared in the Technics RS1500 series.

Leevers Rich used the Isoloop principal on two machines in the early sixties. Not a great system for broadcast use though.

https://www.google.com/search?q=leev...jHknkiaNl5Qb8M

[raditechman]

The mention of Leevers Rich reminded me that many years agoI met the Norman Leevers at his home in Twickenham. He had a workshop there and good sounding HiFi system.

John

[barrymagrec]

Originally Posted by raditechman

The mention of Leevers Rich reminded me that many years agoI met the Norman Leevers at his home in Twickenham. He had a workshop there and good sounding HiFi system.

John

He also had 16 and 35mm optical sound recording equipment upon which he recorded the Leevers Rich Laboratories optical test films, I think the only range of optical tests recorded in the UK.

[rontech]

It has always seemed strange to me that optical sound recording was not developed for multichannel stereo music recording quite early on. The BBC could have used optical tracks to record radio programmes too.

I can't remember offhand what the width of the optical track was on 35mm film. It would seem relatively simple to put at least 6 separate tracks in the space usually occupied by the picture.

The technology was all there from the inception of sound films in about 1928. All the processing plants were available to make copies.

I wonder if Mr Blumlein considered this for early stereo?

Am I missing something? Please form an orderly queue

[TIMTAPE]

This may shed some light on what was done by Disney with multichannel optical sound around 1940.

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

[kalee20]

I believe Blumlein's first stereo recordings WERE optical - magnetic recording wasn't good enough, and disc recording was too difficult to implement.

Reading the OP's attachment (I'm halfway through), just impresses me with the achievement of Philips's Compact Cassette. So many technologies developed to make it possible - precision engineering in the drive mechanism; the pure an applied chemistry to make the tape; the plastic moulding processes for the cassette shells; the design and manufacture of the heads; and of course the electronics. And having made it work, then developing to hi-fi standards, and miniaturising it to Walkman-size players.

Coupled with the achievements of the development engineers in the various disciplines was Philips's business strategies and free licensing which made it take off. It's popular in UKVRR to run-down the bean counters, but they definitely got it right for this one.

[barrymagrec]

I`m going to generalise a bit here.

At any given time from the beginning of electrical recording on disc (1925) and the start of optical recording on film at about the same time right through to the widespread use of magnetic tape the quality available off disc was greatly superior, particularly in respect of noise and distortion.

I am sure Blumlein did consider optical recording but the practical difficulties as well as the reduction in quality for a product with an uncertain market would have made it a non preferred option.

I don`t have figures but I am sure that the cost of a 750 foot reel of film with processing would be much greater than a 12 inch disc.

The original soundtrack recording of Fantasia was in optical stereo made by syncing a number of standard optical recorders together. The resultant image shift from left to right and back again makes for hard listening.

Multi track optical recording on a single piece of film would require extremely compact galvos and lenses - probably not impossible but not trivial.

[Ted Kendall]

Originally Posted by rontech

The BBC could have used optical tracks to record radio programmes too.

They did! The Philips-Miller system used a mechanical cutter on a film coated with black mercuric oxide, with a conventional photocell for playback. Quality was very good for the time - roughly equivalent to 1950s 7 1/2 ips tape. Conventional optical recording did not fulfill the operational requirement for near-instant playback. Together with the Marconi-Stille steel tape machines and direct disc recording, it saw the BBC through the war.

Originally Posted by rontech

I wonder if Mr Blumlein considered this for early stereo?

Am I missing something? Please form an orderly queue

He did! Some of his experimental stereo film sound tracks still exist, and he explained stereo to his wife as a means by which a blind man could follow the action of a film. During the war, Philips experimented with stereo recording using a dual-cutter Philips-Miller machine, to good effect.

[kalee20]

Originally Posted by barrymagrec

I am sure Blumlein did consider optical recording but the practical difficulties as well as the reduction in quality for a product with an uncertain market would have made it a non preferred option.

I don`t have figures but I am sure that the cost of a 750 foot reel of film with processing would be much greater than a 12 inch disc.

My earlier post - I meant, his first recordings (for demonstration purposes) were optical, but not that he considered optical as a marketable technology.

Just thinking, if I'd been in his position and wanted to record twin tracks: magnetic tape with two heads (separated by a few inches) would do, if decent-quality tape recording was possible - but it wasn't. Disc recording, either with two separate grooves, twin-start spirals, or one groove running from edge to middle and another from middle to centre, and two standard pickups, would be possible as long as they were started correctly. Or optical, with twin off-the-shelf light-valves, with mirrors and lenses to get the beams side-by-side onto film (which needn't be 35mm of course).

Developing the twin-coil, 45degree/45degree cutter and pickup, as used now, would have taken weeks - for something which may not be particularly impressive at the end of it.

[Ted Kendall]

Blumlein did use a single-groove stereo cutter, but left modulation was lateral and right vertical. Simple matrixing allows the few sides which have been made available (Beecham conducting Mozart) to be played back, but the difference signal has to be pulled up a long way to get any image width. When I discovered this in 198-something, "Robbie" Robinson, who was one of Blumlein's assistants at the time, was still alive and told me they had concluded that the difference amp must have been faulty, as they couldn't ge much width out of those sides at the time, either.

[barretter]

Going back to the original article I find it most interesting for its history of the Japanese tape-recorder industry ; but it is odd that he doesn't mention IEC/CCIR equalisation and implies that NAB became the world standard.

[barretter]

If you want to judge the quality of the Philips-Miller method you can hear 11 tracks by Django Reinhardt and the Quintet of the Hot Club of France recorded by Radio France using it in 1947 on "Django Reinhardt - the electric years" (Avid Jazz AMSC 920). The sound is very acceptable.

[dave walsh]

That LP "sounds" interesting barretter-musically and technically.

Re optical recording [posts 9* and 13*]. When I was applying to get a job as a Trainee Sound Recordist for the Beeb 5 man Film Crews, it was 16mm stock for the images and sprocketed magnetic tape for the sound track, so both could be run through the editor and synchronised. It wasn't optical sound of course but what sort of reproduction would be achieved there Ted? Pretty good judging by some of the output I imagine, eg Jonathan Millers "Alice In Wonderland". What would it have been equivalent of in 1966 for example? I'm not sure that I ever knew the fr etc of that audio system

Dave W

[Ted Kendall]

16mm sepmag was equalised to CCIR curves for 7 1/2 ips, as the speed is similar. The track width helped with s/n ratio, making for quite a decent system, certainly usable to 15khz. 35mm film was used by some engineers in the States in the early 1960s for its better s/n ratio than contemporary tape.

[dave walsh]

Thanks, yes that does look pretty good Ted but maybe a bit too cumbersome for more widespread use? As indicated, Optical Sound could certainly provide good quality from very early on but perhaps that was a bit impracticable for other uses as well?

Dave W