The magnitude of tape noise: Douglas Self

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A state-of-the-art tape recorder (let's say an Ampex ATR-100) has a quoted signal-to-noise ratio of 69db, unweighted, at 15ips using NAB equalization on Ampex 456 tape. This is referenced to a maximum recorded level (3% THD) of 9 db above (1040 nWb/m) operating level. Thus, the noise (30-18KHz) is about 60 db below the nominal operating level of the machine. Perhaps a little bit better than a vinyl record.
 
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Presumably that is why Dolby A was so widely used in the recording industry from the 1970s onwards?

I am not particularly aware of tape noise from my machines such as they are, but certainly am aware of it on some LPs I own where it is audible during quiet moments and between tracks.

I would be surprised if most vinyl exceeded 60dB unweighted, most inexpensive turntables had rumble levels that were far higher than the noise levels of typical recordings, that is what I remember most from my youth.. LOL
 
Presumably that is why Dolby A was so widely used in the recording industry from the 1970s onwards?
No doubt about that! But, some recoiled against its use even though it reduced the noise. Dolby 'A' kinda 'put a blanket' on the sound, although mildly---I never could put my finger on it because the frequency response always measured dead flat to 20KHz and beyond. Maybe it had to do with slew-limiting or some such. I have never noticed the effect when using Dolby SR, however. SR is the savior of analog tape, IMO.
 
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I'm only a dabbler, and playing mostly tapes I've recorded at 15ips or commercial reissues from AP, TP and others. I don't primarily notice noise as an issue, the sound quality of these tapes are a mixed bag, and I doubt any of the Otaris I own are really doing the good ones justice. I have heard that SR noise reduction is more subjectively satisfactory than A from other recordists, but I only know one person still actively recording to analog tape locally, and a few in my FB group.
 
Due to time constraints I have not read the various sources and links posted so this may be VERY "old hat" and irrelevant. (My apologies in advance.)
Back in the '70's JLH ran series of articles in WW about a diy cassette design. He made some interesting observations about noise. The one that stuck in my memory was that he found the S/N ratio of the bias signal was relevant. If not high enough he found that, in his words, "it was wiping the tape dirty".....
Cheers Jonathan
 
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I have a lot of Otari threads over there and run the only Otari specific group I am aware of on Facebook.. LOL

I love Tapeheads, but most of the members are not highly technical. I post regularly to repair threads on MX-5050 series B2 and MKIII as well as MX-50 and MX-50 II - decks I know a lot about.

We seem to have dragged this thread a bit off-topic.. Sorry!
 
Well, that's true---lots o' tape newbies there @ tapeheads! But a few really knowledgeable dudes that can be really helpful.
Back to tape noise, though, I have noticed that the price of Dolby SR units has dropped dramatically in the past years; so that it's now affordable to put 'em on home machines.
 
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Subjectively I haven't found noise to be a problem, I must be deaf.. LOL I do use SM900 tape and have calibrated all of my decks to use it. I record fairly hot.

I will have a look though, I assume these processors have balanced I/O as they aren't much use to me otherwise. (Outside of the strain gauge and RIAA pre-amps everything in my system runs in the balanced domain)
 
One reason SR sounds more transparent that A is that A has low level tracking problems. Some quite serious, some not. Depends actually on the specific card. My A cards don't track each other well, but track themselves OK. My SR cards are much, much better. The design of the Cat. 22 was challenging for the time, the necessary precision was simply not practical in an all-discrete system. Remember that Dolby A was introduced in 1965, the Cat. 22 in the early 1970s. SR had 20 years of electronic component development to work with. Hence, the sliding band idea was actually achievable by then.

Just a side note, Even though Dolby A was sometimes challenging, its transparency was largely due to the fact that at loud levels it did next to nothing.

Tape noise specs are difficult because they change with reference level, usually the 3% point, which changes with tape formulation and specific bias adjustment, which is also machine specific. As an example, in the old days I could hit 456 with much higher bias levels, maintain flat response, and lower distortion on an A80 than I ever could on a 5050. The result was two different 3% points, and thus two different S/N ratios using the same tape and speed.

Might as well mention bias "purity" and "symmetry" here too, since it plays a role in noise. Asymmetrical bias and erase current has a DC component that raises low frequency tape noise. It was an issue on some early pro machines.

Then people played around with reference levels, trading higher peak distortion for lower noise. With tape, you aren't clipping at 3%, you're mushing.

Then we get into measurement issues, weighting (A vs C), etc., which also relates to tape speed. The noise spectrum bumps up when the tape moves faster, logically. And track width changes it too, there's a small advantage to the wider butterfly heads over NAB for 2-track, but that's also why we flirted with 1/2" 2-track at 15 and 30 ips briefly, no NR required. Double the track width, pick up another 3dB of S/N. Double the speed....and so on. That was all happening during the inrush of digital, which ultimately ended up far less costly for far better performance. 1/2" tape at 30ips is expensive! And really only useful as a master, which then caused issues for the guy cutting the lacquer. Yeah, it was nice, but painful. 14" reels of 1/2" for 30 minutes at 30ips. Mostly we stayed at 15ips.

Anyway, Tape S/N? It was what it was, pick your number and means of getting it. But in pro machines, and most consumer too, moving tape at any speed produced higher noise than the electronics, pretty much always, so long as you had the head shield in place and got the A/C power mag field hum out of it. I can only think of a tiny handful of machines that had excessive noise in the electronics. I think the Telex/Magnecord machines were pretty bad. But fortunately, they're mostly gone.
 
Subjectively I haven't found noise to be a problem, I must be deaf.. LOL I will have a look though, I assume these processors have balanced I/O as they aren't much use to me otherwise.
You may want to take a look at this article that I copied from "Swiss Sound". An interesting take on the benefits of Dolby SR.
......EDIT......Well, it's too big to load. It's the July 1988 issue #23 of Swiss Sound.
 
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Hi dotneck335,
I am NOT a tape expert but it wasn't the frequency per se that he was discussing but the S/N of the bias waveform.....As I recall he was suggesting that unless the bias signal was sufficiently "quiet" it was adding noise to the tape as it was used.
I hope I've expressed his argument correctly. I'll try and chase up the article and explore it a bit more......

Got it: There were three original articles (May, June and July 1976) but the relevant information is contained in a postscript WW Feb' 1978 page 35ff.
Page 36 contains the material i was referring to. Interestingly he throws out some alternatives for the bias such as triangular wave forms.

The link: https://www.americanradiohistory.com/UK/Wireless-World/70s/Wireless-World-1978-02.pdf

Cheers Jonathan
 
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You may want to take a look at this article that I copied from "Swiss Sound". An interesting take on the benefits of Dolby SR.
......EDIT......Well, it's too big to load. It's the July 1988 issue #23 of Swiss Sound.
Found the link!!:
https://www.reeltoreel.nl/studer/Public/SwissSound/SwissSound23eJul88LR.pdf
"Dolby SR does not stop at noise reduction: it goes on to achieve very considerable reductions in distortion and improvements in transient response compared with conventional analogue recording. The modulation noise and high level saturation which have for many years been unavoidable byproducts of tape recording are also rendered inaudible. Whilst SR will dramatically improve any recorder, the better the machine, the truer the sound."
 
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