The demo examples of plangent are very impressive. Although extracting the bias frequency from a 40 year old tape would initially make one consider them bonkers!
Scrape flutter is real. Some tape playback systems have less, depending on the addition of precision rollers added to the tape path.
Plangent was part of the 2008 Grammy Award for Best Historical Album, where is it suggested here [pdf] that they used residual 60hz hum on the recording to do the correction.
Yes, it is! Even my homebrew tape deck has such a roller:
Edit: Actually, there are two of them: one more between the recording and playback head, though much smaller.
Cheers, E.
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Ah, looks like they have multiple strategies. I'd only noticed their magic tape head technology.
You would need to differentiate between hum in the recording and that reintroduced by the playback pre-amp and then there's 50/60Hz. I can't see an LP playback setup devoid of any new hum. Speaking here of home not laboratory conditions.
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60 (or 50) Hz mains hum is (@ least) a very stable and accurate standard.
For some reason grossly underutilized.
We used it for decades in the film industry. Nagra recorders would often have a 60Hz control tone.
Tape binder was often responsible for tape scrape noise. It was an FM modulation (very physical) created mechanically. As a side note, Agfa could make almost any machine squeal, Studers included. The residue was not visible under normal viewing, but Methyl Hydrate would clean this off. Probably Ampex head cleaner would as well, nasty stuff!
Those rollers you are referring to were called impedance rollers by Studer and by some at Tascam. I worked with the studio tech at The Metalworks for a bit. Incidentally, Dave built a tape baker that would reset the binder allowing you to get at least one play out of old masters. The idea was that you dubbed the old master onto fresh stock in a one shot deal. I do know they rented that oven out to other studios. Apparently it really worked.
-Chris
Those rollers you are referring to were called impedance rollers by Studer and by some at Tascam. I worked with the studio tech at The Metalworks for a bit. Incidentally, Dave built a tape baker that would reset the binder allowing you to get at least one play out of old masters. The idea was that you dubbed the old master onto fresh stock in a one shot deal. I do know they rented that oven out to other studios. Apparently it really worked.
-Chris
Same reason, I suppose, that AD makes IC amps with extreamly low distortion.
BTW -- now after tuning up the notch filters, the instruments THD+N is -127dBV now.
[working to be verified a.t.t.]
THx-RNMarsh
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The 60Hz freq stability is +/- 0.1% from the massive generators at hover dam. I think that is short term. Long term average freq stability with constant correction should be much better.
Our ac powered wall clocks depended on the 60Hz accuracy.
THx-RNMarsh
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Yes...looking a bit more into it, it seems the use of 60hz-hum may have been one of several backup techniques used when the bias signal was unrecoverable. But I'm not sure. It's hard to extract the technical details from the popularized accounts that resulted from Kevin Short's grammy win victory-lap/PR-tour. Short only seems to talk about using the power-line noise for reconstruction [page][mp3 2:15-3:05] , but maybe that's because he worked on that part.
The detailed answer is supposedly in the 72-page book that comes with the album. I don't have the album or book. I've only found these comments which summarize:
If it started with a wire recorder there would be no RF bias. RF bias was not introduced until later. There may have been a DC bias which would raise the noise floor.
Film recording used a 60 Hz sync track which was then used to drive the syncro motors in the dubbers to transfer to mag film. Given the difficulty in getting a stable precise motion for film and tape in the 50". 60" and 70's it worked quite well but was big and clumsy and mostly passed with digital recording and widespread use of small crystal oscillators. The Nagra used a second stereo head to record the track over the full track mono in a way that would cancel on playback except with the matching head.
Film recording used a 60 Hz sync track which was then used to drive the syncro motors in the dubbers to transfer to mag film. Given the difficulty in getting a stable precise motion for film and tape in the 50". 60" and 70's it worked quite well but was big and clumsy and mostly passed with digital recording and widespread use of small crystal oscillators. The Nagra used a second stereo head to record the track over the full track mono in a way that would cancel on playback except with the matching head.
20th century ..
I'm starting with PPM source , amplifying with PPM silicon.
Then I end up with the mess that my physical drivers (loudspeaker) make of this
perfection.What am I missing ?
Subjectively , I'm listening to 200W aggressive rock now , the amplification
is absolutely stellar. What could the guru add to this ?
Could he give me a source that would make my -200w more stellar ?
PS - I'm PC- DAC - 200W amp - straight shot !!)
OS
I'm starting with PPM source , amplifying with PPM silicon.
Then I end up with the mess that my physical drivers (loudspeaker) make of this
perfection.What am I missing ?
Subjectively , I'm listening to 200W aggressive rock now , the amplification
is absolutely stellar. What could the guru add to this ?
Could he give me a source that would make my -200w more stellar ?
PS - I'm PC- DAC - 200W amp - straight shot !!)
OS
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