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Odd-Even Numbered Tracks Phase Pattern: Multitrack Reel to Reels
Old 18th June 2017
  #1
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Question Odd-Even Numbered Tracks Phase Pattern: Multitrack Reel to Reels

Hey y'all,

Quick question: is there some sort of 0, 180 phase pattern relationship between odd and even tracks as a standard on multitrack machines? I have an Otari 5050-8 where all of the odd tracks (except 1) are + forward and all of the even tracks are - forward. This is not a pin 3 hot issue. I am guessing this is either a wiring error or some way for the machine to achieve better crosstalk spec / higher levels of side-by-side bouncing without feedback, but I'd like to know for sure. Am I better off reversing the machine's inputs, outputs, at the heads, or some other solution to achieve phase coherency for stereo pairs?

Thanks!
Old 18th June 2017
  #2
Lives for gear
In all the years I dealt with analog multitrack, I never heard of this kind of a standard. And it would have to be a standard, or else tapes wouldn't be compatible between different machines.

Certainly this was never a standard for 2-track machines.

I also can't see how it would buy you better crosstalk specs, unless pairs of tracks carried absolutely identical material (and why bother?). Whether polarity is reversed or not, there'll be random phase relationships between any two non-identical complex waves.

I could be missing something. I suspect somebody just miswired the heads.

(FWIW, the one case of intentional polarity reversal occurs in pilottone sync: Nagras and similar machines recorded the production audio as full track mono across the 1/4" width; they recorded the 60Hz pilot using essentially a two-track head with one winding reverse polarity. That way you could get the full benefits of full-track s/n where it counts, with no interference from the sync signal... and get the sync signal without pollution from low frequencies in the production track.

(I could always tell when someone at a music studio helpfully 'dubbed' a location track for a client: they'd take a single output from 2-track machine. Meaning there was a 60 Hz hum you couldn't get rid of.)
Old 19th June 2017
  #3
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Ended up being on the rear panel xlr outputs, thanks.
Old 25th June 2017
  #4
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It's a good idea - whether standard or not. Because it reduces cross talk ... anything that leaks into the adjacent track is inverted in polarity and therefore summ negatively - reducing the leakage.

Edit: in reply to Jay Rose .. it's not about the signal that is intended to be on the track. It's about the signal that is *not* intended to be there - the leakage from the adjacent track. With *is* the same between the two. So flipping the polarity is a good idea if you want this to sum negatively rather than summing positively.

Seems like the last user of this machine understood this and used this trick.

I learned this trick for reduces crosstalk between hexaphonic pickups on guitars.
Old 25th June 2017
  #5
Lives for gear
Thank you, Kiwi... yes, I now see what you mean. And it would reduce crosstalk during sync mode.

The downside, of course, is compatibility for playback at other studios. Easily fixed if the other studio knows about it and has balanced wiring with phase switches on their console.

Funny, though... back in multitrack days, I never saw a tape box or track sheet labeled for inverted tracks.
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