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Owen Y

Ray Dolby

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aka Ray Dobly! ... RIP.

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Yes, this topic has provided some spirited debate on the Altec board - which seems to be down, as I was looking for some finer quotes to spice the mix!

 

But suffice it to say, Mr. Dolby, while credited with helping with the general success of the noise reduction sector and thus cassette tapes and the movie industry, was not looked on kindly as an innovator.

 

Indeed he was mentioned in the same breath as Bose, and Edison (as in the "inventor" of the light bulb and the electric chair - where one got "Westinghoused" by AC current).

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I'd often wondered about that. As a kid starting out with (very crappy) hifi, cassettes were all I had. Pre-recorded ones that stated Dolby NR, A or B just seemed to have all the highs knocked off when the Dolby switch was flicked.

Stuff recorded by myself from LP's on friends parents systems in Dolby seemed to have the same effect. I soon learned to avoid those switches in order to hear things properly and put up with a little hiss at low volumes.

 

Was I doing something wrong?

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No - I saw the same thing. I avoided Dolby after I bought a Nak (albeit a low end one) when I was in Uni and making good money as a tuxedo'd waitron unit, and used high quality tapes.

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He bought the CBS SQ quad patent for next to nothing and adapted it to Dolby Home theatre AC3, etc.

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Could never get Dolby to work for me even though it seemed to inhabit most cassette players of the era

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Guest

I found the better your system, the less you need bandaids like Dolby NR.

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"I'd often wondered about that. As a kid starting out with (very crappy) hifi, cassettes were all I had. Pre-recorded ones that stated Dolby NR, A or B just seemed to have all the highs knocked off when the Dolby switch was flicked.

Stuff recorded by myself from LP's on friends parents systems in Dolby seemed to have the same effect. I soon learned to avoid those switches in order to hear things properly and put up with a little hiss at low volumes.

 

Was I doing something wrong?"

 

No!!... just another example of a less than well set up cassette deck, usually azimuth and dolby level, and dodgy hi speed duplicated pre-recorded tapes. Dolby A was the studio job, B and C the domestic beasties, and later S, which was very good but the Cassette was all but dead by then.

 

 

With a bit of care, it is surprising what can be eeked out of a good quality cassette deck .

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Nak-Mad;189365 wrote:
"I'd often wondered about that. As a kid starting out with (very crappy) hifi, cassettes were all I had. Pre-recorded ones that stated Dolby NR, A or B just seemed to have all the highs knocked off when the Dolby switch was flicked.

 

Stuff recorded by myself from LP's on friends parents systems in Dolby seemed to have the same effect. I soon learned to avoid those switches in order to hear things properly and put up with a little hiss at low volumes.

 

 

Exactly my experience, and I did not even aspire to the heights of azimuth adjustment, the distinction was clear, Dolby sucked the tops out, and probably more.

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Sorry Declannz!

I have lifted your quote from Nak-Mad's

Apologies.

Jim

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Papa Hemi;189384 wrote:
Exactly my experience, and I did not even aspire to the heights of azimuth adjustment, the distinction was clear, Dolby sucked the tops out, and probably more.

 

Papa,

 

Unfortunately that is a common experience, and lead to the Dolby B system on your average domestic cassette deck being much maligned.

Most of us in our younger days would have been using a 2 header with fixed bias/eq/level....and Dolby B NR... I know I was, and my initial experiences were similar.

 

Dolby B is a level dependent system, so performance is wholly dependent upon how the deck is set up in terms of bias/eq/level, and what tape type it was calibrated for... generally not the low bias Lamphouse LN in common student use!

 

First off, if the music you recorded didn't playback within 1-2dB of the level you recorded it at, then you were going to have problems with Dolby 'tracking'. A quick test would have been to record a tone in the 300-1kHz range at 0dB and play back.. if the playback was more than 2dB down.. you are going to lose the highs. Some blank tapes can have a level mismatch of 8-10dB, so you are completely screwed. Not necessarily bad tapes, just doesn't suit your deck.

 

Hence the old adage, find the right tape and stick with it...

 

Generally, most Japanese decks were set up for either the TDK or Maxell mid range tapes...

 

Then add in the alignment problems that could be created by over vigorous cleaning, upsetting the original azimuth, ( & tilt ) the first to go are the highs....

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Pasted from a recent email to an acquaintance:- lazily!!

Perhaps a little drunk at the time ... as now, perchance even!

Party? No ... just a comment from a few days ago;-

_

 

- and it was one of the lost tangents of our conversation that I was going to mention re your cassette deck - everybody sort of knows about cleaning the heads (isopropyl alcohol) - but most forget or don't realise, even though it's usually in the manual, that the tape heads also need to be demagnetised periodically... (they used to suggest once a week cleaning, once a month demagnetising)

 

Teaching science - not sure what branches, but assuming a general knowledge! - you can imagine that, just as you stroke a screwdriver *in one direction only*, moving it away for the return stroke, to magnetise it (very handy for keeping screws & bolts on the end!) - so, too, the very permeable heads are being continuously stroked in one direction by the ever so slightly magnetised tape... the waveforms imprinted on it won't necessarily be symmetric - and thus the heads gradually become increasingly magnetised... and when their magnetism starts to become equal to the weakest (highest, finest frequencies recorded, high treble etc.) signals on the tape, it strips hem and replaces them with noise... so your cassette tapes gradually become duller & hissier... sound familiar?

 

Eventually (lots of cars had cassette players) you'd start listening to commercial Dolby B recorded cassettes without Dolby, which brought back a bit of treble for a while, but it would just get worse...

 

The taped music can never be restored, but demagnetising the heads will ensure that any new tapes recorded would be pristine and clear again; for those with a tape collection, best to re-record over them from CD, etc.

 

For cassette decks, you'd use a device like this: http://www.trademe.co.nz/Browse/Listing.aspx?id=641796182

 

To de-magnetise, you need a decaying alternating (AC) magnetic field.

 

In those, an audio oscillator with an amplitude decay function is built in, powering it's own head, in a cassette case - when you insert it & press play, the two heads engage and its field demagnetises your decks head. Turn up the volume slightly, you can hear it - maybe at 1kHz or a few hundred Hz, it's all over in a second or less.

 

For larger heads like on a RTR deck, usually a mains-powered wand is used (essentially a solenoid with an extended tip, covered with a soft plastic) at 50Hz, and waved around in circles at the head, starting close and pulling right away gradually, getting a decaying alternating magnetic field that way...

_

 

For what it's worth!

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E&OE, errors & omissions excepted... a few typos there! ;=})

 

But (another thread) I still own a tape deck, the first serious one a Sony TC-RX80ES, late 80's early 90's, the main one last in use, not that ultimately great perhaps but still something at the time;- since, a couple of real ES decks needing restoration arrived, but I found that with heads de-magnetized and TDK SA90 & other exotic chrome or metal tapes, it sounded pretty good, experimenting with Dolby B & C and off... fantastic to put on a dolby c at high volume with no noise and a few seconds start and walk away, you'd not think a tape was playing... very quiet!

And then very loud!

 

Yes you needed to set up bias correctly, and the RX80ES had facility for it.

 

So, I still think the heads de-magnetisation physics has been overlooked...

 

But yes, I also tried & experienced the differences recording without dolby b or c on equally good tape... depending on the music and state of mind perhaps;- I only have those recorded at the time, and in those cases whether it was recorded with dolby b or c or none is marked, and I have accepted it as it is (and set the deck accordingly).

 

Still have some TDK SA90 sealed actually, plus all the used & some metal, must look see & hear into it all again, some time! ... ;=})

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I still have a handheld demagnetiser & also a cassette-cased one, somewhere.

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Owen Young;189803 wrote:
I still have a handheld demagnetiser & also a cassette-cased one, somewhere.

 

Likewise,... magic wand for the RTR's, but prefer the TDK head demag cassette unit for the cassette decks.. more convenient and seems to do the job as well as the wand. Generally demag whenever I do a clean............

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I have one of those TDK cassette demagnetisers - not 100% sure how effective it was.

 

It seems tape users are still divided over the worth of demagging.

 

Heads seem to self demag to a degree, its capstans and other metal parts that need a manual wand type demag ?

 

Need to be careful with those things.

 

:D

 

Eg.

 

158678=7434-045 janfeb87 p173.jpg

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I have one of those TDK cassette demagnetisers - not 100% sure how effective it was.

 

It seems tape users are still divided over the worth of demagging.

 

Heads seem to self demag to a degree, its capstans and other metal parts that need a manual wand type demag ?

 

Need to be careful with those things.

 

:D

 

LOL... yep, almost as divided as over the use of IPA to clean heads, capstans and pinch rollers. I don't hold a banner in either direction and there seem to be some credible people in both camps, so just go with my own experience. The consensus on the it's much ado about nothing side is that the cassette tape 'field' is nowhere near strong enough to impart magnetism in anything, let alone any permanance, or is it remanance!?!, and the operating solenoids and motors are more likely to do harm... the other, well... it is all a lot of coercivity and physics 'stuff' way over my head :eek:

RTR's may be a different story...

 

I like the little TDK cassette demag unit for it's convenience. Though I have a good hand held unit for the RTR's, I've never been game to take it anywhere near a cassette deck, and in fact use it very seldom on the reels, for reasons your cartoon alludes.. can be a double edged sword!.

 

In most cases, I haven't been able to detect any significant difference before and after using the TDK demag on most decks I've played with, (and it's use doesn't appear to do any harm either) but on an old Technics RSM-63,(3H) it did seem to lower the hiss level on playback.

 

There seems to be some agreement at least in that is doesn't affect 2 head decks, as putting the deck into 'record' is as effective as any demag.. so if that theory is correct by the time the tape leader has passed the heads, it is effectively demagged. So, if you want to demag your 2 header, just whack it into record mode for a couple of seconds periodically.. problem solved!

3 headers are supposedly the problem decks and it is the separate playback head that needs demagging. I haven't read any treatises on the issue of demagging and siamese vs discreet heads.. seems to have been over looked?

 

I have conducted the HF magnetic erasure tests as promoted on some forums as a check, a long time ago using a Nak 582Z and a T-100, and don't recall any drop of in signal level of a -20db 15kHz tone after multiple plays (25+) of the same tape.. but then my methodolgy could have been flawed or equipment too basic.

 

Either way, I don't sweat over demagging or get paranoid about it, but do give my machines the occasional treatment !

 

When was the last time you demagged your ZX-7, and what differences did you notice?

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That's a similar result to when I carried out similar tests (on my old 480 and a friend's 582), back when TV & Sound had fancy test stuff like a T-100.

 

Last time I demagged the ZX7 would have been about a a year ago when I re-discovered my TDK demag thingy - minus user manual and packaging etc. - then i went on a demag marathon - ZX7, the Walkmen Pros.

 

No consistently audible improvements were noticed.

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Ray Dolbys patent filed in 1969, one would have to conclude borrowed heavily from much earlier patents such as those of Murray Crosby in 1953 describing a FM Modulation system and clearly explaining emphasis and de emphasis.

 

DBX and its found David Blackmer were well ahead of Dolby, providing a better invention -noise reduction in the form of Companding, that unlike Dolby has just as much relevance today. To compand is to compress when typically recording, and to expand on playback giving up to 20db of added dynamic range. The DBX Type 1 companders offer in company with products like Yamahas CDRHD1500 ability to improve conventional CD reproduction.

 

Chris

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Unfortunately those early dbx Type I and II were only single band companders (cf. 4 band Dolby A) and suffered from very audible side effects like pumping where background noise levels were modulated by the music.

 

But what really killed dbx on the consumer front was that while Dolby B encoded tapes could be played back OK on non-Dolby gear, dbx tapes were all but unlistenable on non-dbx gear. Ditto for dbx encoded LPs.

 

Dbx was given a respite from domestic obscurity with the advent of consumer VHS H-Fi recorders which used a proprietory version of dbx noise reduction.

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Hi Michael

There are none of the artifacts you describe with Type 1 DBX, I am happy to demonstrate if you want to call around.

 

 

Chris

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Hi Chris,

 

I don't know about that Yamaha CD recorder you refer to but IME with various consumer dbx cassettes decks (eg. Teac, Technics, Yamaha) they all had audible artifacts to varying degrees and basically just didn't sound very good.

 

Especially disappointing was a Yamaha K-1020 with a full suite of Dolby B/C NR, Dolby HX Pro and dbx type II.

 

In today's digital world dbx is just as irrelevant as Dolby.

 

Did you ever try High C ?

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