Is it possible to compensate for incorrect bias? (to use cheap tape and not rebias?)

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Blue Jinn

Blue Jinn

Rider of the ARPocalypse
OK, this sounds silly, but I have an A-8 that is calibrated for 456 type tapes. I don't want to run 456 on it (1 mil is recommended) and I have exactly one reel of 457. (and one of 041 of unknown vintage, and some 407 of SSS vintage.)

I have 642 and Maxell UD, while not back coated are good tapes, and appropriate O/L. I also have a stack of 641, that I would like to use for knocking about. AFAIK, the bias requirement for 641 is lower, based on the spec sheet I have for it (which could be wrong) 260 Oe vs about 310-320 for the other tapes. I've seen specs for 641 from 260 to 290, but given my previous experience with it, I'd suspect the lower figure.

I did some recording on my Teac deck (and have another thread on that) and the 641 was "muddy" and "dull" which I'd expect from the incorrect bias. I'm not about to adjust the bias, can I compensate somehow (kinda like DAT "Pre-emphasis" ) by boosting the highs before going to tape? The Dolby C does a great job of eliminating hiss.

Yes, I'm trying to squeeze all I can out of the tape stock I have.... Although I also have a ton of 632, which while technically 1.5mil, is thin enough that I think it's safe to use on the Fostex transport. Opinions welcome on that as well.
 
In my experience, I would say that you normally can swap tapes within certain limits ... but I'd say 641 and 632 are too far off from 456 to use without re-calibrating, unless you're going for a specific effect. There are things other than EQ going on (distortion, etc) that may be undesirable.

basically, if your ears are telling you it's pretty far off, it's probably a bad idea.

I do like changing around tapes, and using the 'wrong' tape ... it can give you interesting colors, sometimes even better than the 'correct' one. I've heard that some people liked to setup their deck for Ampex 456 and use Agfa 468 on there (I've done it and it sounds a little brighter/punchier). But those tapes are pretty close anyway. I've used Scotch 111 on a machine setup for 203, and it sounded reasonably close. I've also used 203 on a deck set up for 206, and while it was a little more murky, it sounded cool and still retained the character of the tape. but i've also placed a reel of (I think) Ampex 434(?) on a deck set up for 203, and it just sounded bad. And using 111 on a deck setup for 206 sounded bad as well.

so, basically, I'd say you can play around and see what you get ... but it you're hearing something that sounds unpleasant, it's not likely something you can 'correct' with EQ.

that said, I love those old '0' level tapes ... in some ways, better than the high output, backcoated tapes. So I'd say it's worth re-calibrating your deck to use them.
 
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Blue Jinn said:
I did some recording on my Teac deck (and have another thread on that) and the 641 was "muddy" and "dull" which I'd expect from the incorrect bias. I'm not about to adjust the bias, can I compensate somehow (kinda like DAT "Pre-emphasis" ) by boosting the highs before going to tape? The Dolby C does a great job of eliminating hiss.

Yes, I'm trying to squeeze all I can out of the tape stock I have.... Although I also have a ton of 632, which while technically 1.5mil, is thin enough that I think it's safe to use on the Fostex transport. Opinions welcome on that as well.
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Yes you can try and compensate for an overbiased tape by boosting the treble but you dont get anything for nothing. Overbiasing actually erases the signal as it's being recorded. If you boost treble or level in general on the way in, you will run into saturation and distort earlier than normal. You lose headroom.

On Dolby C on your A8. Dolby C is very sensitive to bias level. It has to be right to avoid Dolby mistracking. Not as bad on a reel to reel machine running fast speeds as a cassette but still pretty touchy. If you try and use Dolby C with older low energy tapes like 632, it will sound like shit.

Unfortunately, even for a tech, aligning and rebiasing a 2 head machine like an A8 is a PITA. If you must use old low energy tapes without a proper alignment and rebias , if it's possible, disable the Dolby C. I cant remember if there is a switch for it on an A8. Might be worth having a look.
 
Beck said:
The problem with high frequency pre-emphasis is that high frequencies add to the bias, so if you already have a situation where you’ve got your tape over biased you’ll just add even more bias by cranking the high frequencies going in.
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Exactly. It becomes a runaway situation.
 
Tim Gillett said:
Unfortunately, even for a tech, aligning and rebiasing a 2 head machine like an A8 is a PITA. If you must use old low energy tapes without a proper alignment and rebias , if it's possible, disable the Dolby C. I cant remember if there is a switch for it on an A8. Might be worth having a look.
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You can switch off the Dolby. I think the off position is something like "External", I don't want to have to dig out the A8 just to look. I tried it once, but only once - the results were appalling.

Out of interest, no-one has mentioned LPR35 yet - while I appreciate he wants to use his existing tape stock if possible, that's the closest match currently in production, is it not? Given that most his existing stock is pretty much incompatible, I'd think that would be the most sensible approach which didn't include re-calibrating the 2-head machine.
 
Thanks everybody. LPR-35 is an option if I want a 457 substitute, and I have plenty of 6x2 and Maxell UD. I just happen to have "acquired" a fair amount of 641, and I don't like to see it go to waste

(Another option is to calibrate the second setting on the Teac deck for it . . .)

I didn't realize "pre-emphasis" would actually make things worse, and I hadn't thought of running a mix or individual tracks through an exciter. I have a few of those, (and a Tascam line mixer (MM200) that has "BBE Process" as a feature.) I'll give it a try. Also as 'fly indicated above, I might get a particularly interesting sound using the "wrong" tape approach! As an aside, the Dolby works well on this machine. I've used 632 and kept the levels appropriate, and haven't had a problem with hiss.
 
also, for what it's worth, when i use the 'wrong' tape, it's usually just for demo mixes, messing around, tape delay effects, etc ... for important recordings, I generally use a tape that sounds pretty close on output to what's going in.
 
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I'm pretty sure the A8 is a 3 head machine unlike the rest of the 8-tracks from Fostex, the A4 we used was.

The two-head thing is the only thing I don't love about Fostex - and the silly plastic transport of the R8.
 
Mine also is only two heads. I wonder if the LR is three. (Perhaps Dave can chime in here?)
 
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