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[jlapointe]

Setting up  a tape today I came across an azimuth issue that stumped me.  Tape was 1/4" 30ips stereo.

My usual procedure is to get a rough azimuth setting with the 1k tone while setting level, then move to the HF tones to fine tune. I use a software scope to check azimuth.

When I put this tape up the 1k tone was not in phase (not uncommon), but could not be put in phase with any amount of azimuth tweaking.  However, the 10k tone was easily tweaked into phase, at which point the 100Hz tone was in phase as well.  If I was aligning the 10k tone to a "false peak" I would think that the 100Hz tone would be out too then (along with the 1k).

The only thing I can think of is that the two channels of 1k tone on the tape were not recorded at the same time or from the same source, ie are out of phase / time alignment completely.

I checked the tape on two machines just to make sure.  Same results on both.

Am I missing anything obvious here?

Best,

- J.

[CWHumphrey]

Your problem is that you're beyond 360 degrees out.

That's why better MRL alignment tapes contained 4kHz in addition to 50Hz, 100Hz, 1kHz, 10kHz and 15kHz(16kHz).

The reason that 100Hz show in phase on the scope is because 100Hz is a much longer wavelength than 1kHz.

If the record machine was beyond 360 out of phase, then you'll just have to live with it.

Cheers,

[Greg Reierson]

You can find your way back by adjusting the azimuth screw for max output at the highest frequency. Then you can fine tune the phase alignment. Remember that the two don't always agree.


GR

[jlapointe]

CWHumphrey wrote on Tue, 28 April 2009 21:00

Your problem is that you're beyond 360 degrees out.

Do you mean beyond 360 degrees out for the 10k tone?

Greg Reierson wrote on Wed, 29 April 2009 00:06

You can find your way back by adjusting the azimuth screw for max output at the highest frequency.

Listening to the mix in mono I tuned for most high end.  That got me back to the same situation, with 10k and 100 in phase and 1k out.  Here's a picture of the best case:



Thanks for your help.

- J.

[TotalSonic]

J -
I'm wondering what happens when you try to adjust the wrap and/or the zenith.

Best regards,
Steve Berson

[Greg Reierson]

Is this a second generation tape like a safety copy of a master?

You haven't mentioned how it all sounds?


GR

[jlapointe]

TotalSonic wrote on Wed, 29 April 2009 23:20

J - I'm wondering what happens when you try to adjust the wrap and/or the zenith.

Wrap and zenith are absolutes related to proper tape to head contact, independent of what is on the tape.  

[jlapointe]

Greg Reierson wrote on Wed, 29 April 2009 23:22

Is this a second generation tape like a safety copy of a master? You haven't mentioned how it all sounds?

First generation mix master.  Once I tuned for max high end it sounds ok.  I'm trying to track down a digital backup from the mix studio to compare.  I'm discovering I'm beyond obsessive when it comes to reproducing a tape properly.  Personality flaws of the mastering engineer ...

[TotalSonic]

JLaPointe wrote on Wed, 29 April 2009 22:29

TotalSonic wrote on Wed, 29 April 2009 23:20 J - I'm wondering what happens when you try to adjust the wrap and/or the zenith. Wrap and zenith are absolutes related to proper tape to head contact, independent of what is on the tape.

Understood - however I've experienced seeing some really out of whack readings "fixed" by moving these to compensate for recordings made on decks that were well out of spec in their alignments.  I have no idea whether it would help in this case - but a small turn of a screw to check might be worth a minute if all else fails.

Best regards,
Steve Berson

[CWHumphrey]

Yes, 10kHz is beyond 360 degrees, but really the whole azimuth is beyond 360 degrees out.

First, make sure your machine's azimuth is correct.  Hopefully your MRL (or equivalent) has several freq. on it.  The Lisajous pattern on the scope should be in phase for all freq.

Then on the record side, you should be able to record any freq. while monitoring on the repro head and all freq. should be in phase on the scope.  Hopefully, your oscillator can do more than just 100Hz, 1kHz, and 10kHz.  Any freq. you send should be in phase on the scope.  If even one is out, you have a problem.

Now if all that is good, and the clients tones come up with a problem, it means the record machine the tones were created on had a problem with azimuth and there's not a whole lot you can do.

Cheers,

[Adam Dempsey]

JLaPointe wrote on Thu, 30 April 2009 12:34

First generation mix master.  Once I tuned for max high end it sounds ok.  I'm trying to track down a digital backup from the mix studio to compare.  I'm discovering I'm beyond obsessive when it comes to reproducing a tape properly.  Personality flaws of the mastering engineer ...

We're paid to be obsessive about such things. In this case I'd now run with it.

Clean tape path.
Set up L/R repro with 1k.
Azimuth adjust for max HF in mono (ignore the 1k).
Re-check L/R repro with 1k.
Check playback EQ LF & HF tones. Tweak to ref if necessary.
Listen to the program & check mono.
If sounds good, you're good to go.
(ignoring NR cal and assuming the tones actually relate to the music progrm).

[jlapointe]

TotalSonic wrote on Thu, 30 April 2009 00:12

Understood - however I've experienced seeing some really out of whack readings "fixed" by moving these to compensate for recordings made on decks that were well out of spec in their alignments.

Can you cite a specific example, and what sort of problem was fixed?  Just trying to wrap my head around (ha, sorry) what mechanism may be at work there other than just skewing the frequency response with poor tape to head contact.

This raises another more general question about handling tapes originating on less than well maintained machines  - say you get a tape on which the 10k tone is 6db up on the left relative to the right.  You bring it back to 0vu on your repro, and now the left channel is noticeably dull with program material. You know they weren't hearing it like that in the mix room. (ie. their repro was probably off and they compensated with the record eq)  

Do you:

A) adjust the repro eq by ear until it sounds somewhat normal?

B) still align to the tones and fix it with outboard.

How would you (anyone here) handle this situation?

Best,

- J.