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Author Topic: help me! please! (analog tape alignment)  (Read 2115 times)

zywot66

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help me! please! (analog tape alignment)
« on: June 11, 2009, 11:49:36 am »

here go's...we had some songs tracked in a studio in S.F. it was then mixed down to a stereo 2track ATR. fast forward 4 months and im trying to align the test tones, 1kHz/10kHz/100Hz. the problem is when i do the azimuth adjustment on say 1k the azimuth on 10k is even worse. then when i make the 10k good 1k and 100hz are way out.  
all fequency bands seem to be in different places in time. i tweeked it so far out of whack that i thought i broke my machine. thank goodness i have an MRL with pink noise on it and a spectrum analyzer to see and then correct the comb filter affect. i cant make heads or tails of it. can i fix this?

also can anyone lead me in a direction for info on decoding an M-S signal from a 2 track stereo mix.

thanks bros!

mike
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TotalSonic

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Re: help me! please!
« Reply #1 on: June 11, 2009, 12:14:12 pm »

zywot66 wrote on Thu, 11 June 2009 11:49


also can anyone lead me in a direction for info on decoding an M-S signal from a 2 track stereo mix.



to decode M/S to L/R:

Keep Mid channel panned straight up center.
Mult Side channel to 2 channels -
pan 1st instance hard left
pan 2nd instance hard right and phase reverse this one.

From there you can adjust balance and width of panning to taste.

to encode L/R to M/S
sum L/R channels to mono - this gives you the Mid
combine L/R channels to mono with R channel phase inverted - this gives you the Side

There are a number of plugins (i.e. Voxengo MSED) and hardware matrixes (i.e. Dangerous Music S/M) that will do this for you as well.

Best regards,
Steve Berson


archtop

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Re: help me! please!
« Reply #2 on: June 11, 2009, 12:15:08 pm »

Sound like you are adjusting the azimuth when you should be
calibrating the electronics.
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Richard Williams

zywot66

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Re: help me! please!
« Reply #3 on: June 11, 2009, 10:54:43 pm »

totalsonic thanks dude! just so im straight here...the method you suggest seems an awful lot like dematrixing an m-s mic signal. what i would like to do is effect(EQ, De-S) the width verse the center signal on a stereo mix down of a finished song. is this what you speak of. dematrixing a stereo mix(complete song) the same as dematrixing an ms mic signal?
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CWHumphrey

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Re: help me! please! (analog tape alignment)
« Reply #4 on: June 12, 2009, 03:13:02 pm »

The azimuth may have been off on the record machine.

Start by putting up you MRL alignment tape and make sure that your machine starts on. The Lissajous pattern should be the right phase relationship for all freq.

If say, 100Hz and 10kHz are right, but 1kHz is out, just put up the 10 kHz tone and adjust the azimuth watching the pattern shift in and out of phase while the meters on the machine climb in level.  

When the meters peak, go back to the 1kHz tone and adjust looking at the scope so that the Lissajous pattern is in phase, then do the same for the 10kHz tone.  100Hz should also look in phase.

After you're sure the azimuth is correct on your machine, then put up the client's tones.  If it's still out at 1khz, but fine at 100Hz and 10kHz, you might be able to adjust 1khz so that it's in, but most likely the record machine's azimuth was out when the tones were printed and there isn't anything that can be done to rectify that.

Cheers,

Cheers,
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Carter William Humphrey

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CWHumphrey

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Re: help me! please! (analog tape alignment)
« Reply #5 on: June 12, 2009, 03:16:39 pm »

I just re-read your post. Since 1k and 10k are in, but 100 Hz is it means that the record machine's azimuth was way beyond 360 degrees out.  There's nothing you can do other than to put up your MRL and playback all available freq. to make sure your machine's azimuth is correct.

Cheers,
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Carter William Humphrey

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Greg Youngman

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Re: help me! please! (analog tape alignment)
« Reply #6 on: June 14, 2009, 08:22:03 am »

Just a thought.  Are you able to play the tape and adjust azimuth by ear?  You know you're there (or close) when you collapse the stereo into mono and don't loose any highs.  If you're unable to get close by ear... it sounds like your playback head could be suffering from gap scatter.  Or, the the tape could have been recorded on a machine who's record head was suffering from gap scatter.  There's nothing you can do about that except to try playing the tape on another machine.
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JJ Golden

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Re: help me! please! (analog tape alignment)
« Reply #7 on: June 15, 2009, 04:49:00 pm »

Hi Mike,
I think you should start by calling the studio in SF and let them know the issues you're having. They should be able to confirm that their machine is set up properly, and help you find out what's going on on your end. If they are unable or unwilling....keep posting here.

JJG
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slothus

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Re: help me! please! (analog tape alignment)
« Reply #8 on: June 16, 2009, 11:14:32 am »

zywot66 wrote on Fri, 12 June 2009 01:49

 the problem is when i do the azimuth adjustment on say 1k the azimuth on 10k is even worse. then when i make the 10k good 1k and 100hz are way out.


Howdy, just wandering through and noticed this.  Maybe I'm missing something (it is late here) but assuming nothing is totally wacked with the physical alignment of your repro head, physical alignment of the recording machines record head (or even some wild inter-channel bias craziness, electronics or eq circuitry weirdness) on the surface this reads symptomatic of being on the wrong peak (pretty wildly on the wrong peak mind you). Are the tones stable? Does your zenith look ok? Any extreme wear pattern? I guess it could be gap scatter as mentioned already but seems more likely to be a split gap if it was related to gap condition.  

Assuming for a second everything is as it should be on both machines i'd eyeball the repro head  and tweak azimuth so the head looks as perpendicular as possible to the tape path. Then i'd turn off the CRO and forget inter-channel timing for a bit and stick one channel's output into a digital peak meter and shoot for the peak short wavelength output. See how that sits versus the other channel. This would tell a lot in itself.
 
For the inter-channel phase relationship part of it I'd sum both channels in mono and again shoot for maximum output on a meter starting at the longest wavelength working upwards. If you shoot for peak output starting down low and working up you'll end up on the right peak (again assuming nothing crazy is going on - If this isn't the case something crazy IS going on). If your machine does 15 and 30 you get 5 or 6 usable tones to play with from what you have printed.  

Apologies if I'm telling you how to suck eggs, just thought it might be of some use.  Pretty much a variation on themes already stated. I'm keen to know what it turns out to be.

BTW, are you sure you aren't having a seniors moment? That eq definately isn't patched in right? Smile

Brent Punshon
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zywot66

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Re: help me! please! (analog tape alignment)
« Reply #9 on: June 18, 2009, 02:04:46 pm »

thank you so much everybody. the wealth of ideas that came up is awesome! this web site rules. i didn't call the studio or anything cause we ended up having digital files as a back up. so i was freaking out for a moment here before i new this. his machine had to be way out of whack. my machine is good. i put up my MRL and aligned my machine. i am kind of bummed that he let it go like this but at least i have some good digital files to use.

thanks again folks.
mg
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