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Analog Tape Trivia


Jeff Wexler

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Which question?  The order shuffles around.

This one:

What's the purpose of bias when recording to analog tape?

x

Reduce print-through effects

Improve high-frequency reproduction

Compensate for the non-linear response of magnetic tape

I read it as setting the bias for a new brand/style of tape so I chose Improve HF repro. Semantics really.

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10/10.  But in the Department of So What.

 

philp

 

For me the "So What" is that it's cool to revisit analog passions and to reinvigorate dormant brain cells.

 

...I think I'll install bias adjustment pots in my Nomad and Deva.  I've been meaning to spring for the 15ips upgrade option, but I don't think post is equipped to handle 30ips Deva files.

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I think the tape speed question actually allowed either answer (better high frequency response / reduced tape hiss) to be correct. 

 

Also, another unlisted benefit of storing tapes "tails out" is that -- if it is accomplished via playback -- you typically have a more even tape pack (than that accomplished with high speed winding) which better maintains the evenness of the polyester for long term storage.

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The bias on a tape recorder was a strong (it heated the record heads) ultrasonic signal between 40 and 100 kHz that reduced distortion caused by the tape's nonlinear response to a magnetizing field. Basically, the iron oxide material would not magnetize for low magnetic fields and then would suddenly magnetize as the field got stronger. Oddly, the tape with bias applied, magnetized as the tape left the field of the record head. The bias was typically the same frequency as the signal applied to the erase head and and erased somewhat the desired audio signal except as the tape was leaving the record head field.

 

Since it erased high frequency (treble) audio signals more than low frequency (bass) signals, you could vary the high frequency response by changing the bias frequency level. This was a secondary effect because the real purpose of the bias was to reduce distortion at all frequencies. Different tapes had different "hardness" or resistance to magnetization. This gave them different treble response and resistance to the erasing effects of the bias. Hence, the bias had to be adjusted for each brand of tape. One of the reasons that faster tape speeds gave better high frequency response, is the tape left the record head's bias field at a faster rate and erased the high frequencies less.

Best Regards,

Larry Fisher

Lectrosonics

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I'll buy the first digital recorder that sounds like Nagramaster @ 15 ips full-track.

 

philp

Isn't there a plug in for that......?

Amongst the vast sub-culture of thousands of retro effects complete with old school graphic representations of the controls?

It's quite interesting how much of this there is, and I've found myself wondering if it's just a way to sell even more, have a modern version of an effect and tweaked retro version with a different name, or is that too cynical? :)

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Isn't there a plug in for that......?

Amongst the vast sub-culture of thousands of retro effects complete with old school graphic representations of the controls?

It's quite interesting how much of this there is, and I've found myself wondering if it's just a way to sell even more, have a modern version of an effect and tweaked retro version with a different name, or is that too cynical? :)

There are a number of such plugins. The better among them are well-crafted to recreate the sonic effects they're designed for.

Some artists (John Mellencamp comes to mind) will do an analog tape pass of their tracks to get the sound they like.

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"I read it as setting the bias for a new brand/style of tape so I chose Improve HF repro."

 

I got that one "wrong" also. 

Same hers. that's the only one I got wrong as well.

And Bias absolutely is related to hi frequency response, as I up have heard that some engineers would actually bias the tracks that had cymbals, hi hats etc not hem differently for enhanced High frequency response.

10/10 and I agree w/ eric about semantics. A lot of legend and myth about tape biasing. Some folks  would set bias for the instrument that was being recorded.

Exactly.

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One of the reasons that faster tape speeds gave better high frequency response, is the tape left the record head's bias field at a faster rate and erased the high frequencies less.

 

I know of rock music engineers who didn't like 30ips because of the infamous low-end head bump problem. 

 

http://www.endino.com/graphs/

 

Usually, the tape ops were so terrified of running out of tape in the middle of a song take, they hated 30ips. (Man, that's exercising a part of my brain I haven't used in about 25 years...)

 

 

5 of 10. Should of been 6/10 on the tape speed question IMO. Oh well, once a C student, always a C student.

CrewC

 
I bet you'd get 10 out of 10 on digital questions...  :mellow:
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I know of rock music engineers who didn't like 30ips because of the infamous low-end head bump problem. 

 

http://www.endino.com/graphs/

 

Usually, the tape ops were so terrified of running out of tape in the middle of a song take, they hated 30ips. (Man, that's exercising a part of my brain I haven't used in about 25 years...)

 

 

 
I bet you'd get 10 out of 10 on digital questions...  :mellow:

 

 

I once 'tape-opped' a take on (probably) an A80 at 7.5 instead of the 15 asked by the engineer. I noticed as soon as we rolled but didn't tell 'til after the take. Since we were recording a bass instrument I mumbled an excuse about bass response which at least made the engineer laugh at my efforts.

 

I've got a IV-S and a IV-SJ which although rarely used are part of my secret weapon arsenal for various SFX purposes: one less obvious one being extreme speed changes (obviously with matching pitch shift). The SJ having an additional 1.5ips setting allowing a 1/100 change with one generation re-record, but even a 1/10 shift betters anything software can manage.

 

I've a small handful of favourite books to remind myself of both theory and practical matters that inevitably fade away when you're no longer lining up the 24 track at the start of a day. One of these is 

 

MODERN INSTRUMENTATION TAPE RECORDING, an EMI handbook from 1978, which has concise, readable but thorough chapters on theory and practice of magnetic recording: intended for instrumentation recorder selection (with chapters on FM and pre-80s PCM etc) but an excellent reminder of theory and a nostalgic night alone at the pub once every year ...

 

The earlier 1970 'How to Choose and Use TAPE RECORDERS' by HW Hellyer, Fountain Press, for the 'home-enthusiast' rather than laboratory or studio, is even better in the nostalgia stakes but less so as a theory-crammer - but makes up for it with an excellent chapter on 'Equalisation, Bias and Noise reduction' which presents all the instances of freq response in the chain in a very clear and readable manner, particularly good for us Europeans who might need to know both the CCIR and NAB standards.

 

Haven't looked at the test yet but agree with Eric and co that that bias question is extremely poorly worded: if the bias isn't working at all, fair enough, 'no sound' - but surely our job is using the equipment (recorder, tape stock) to get best signal/response for type of sound ...

 

Jez Adamson

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