[78-L] shifting phases

[Mark Durnberger]

This approach...what I'd loosely call the "Differential Method"...is also 
one of the radio broadcaster's underrated tools.  Stereo stations can set up 
their audio by transmitting a clean L-R signal while adjusting their audio 
transmission equipment for a NULL as heard on a MONO receiver.  The 
simplistic assumption is that when both audio channels are balanced, their 
combined output will be maximized with an L+R signal, and minimized when the 
signal is L-R.

I posit this thought with full respect for my friends and fellow-listers Bob 
Orban and Bill Ruck, who will tell you it isn't always that simple :-))  But 
this is a terrific starting point and a simple tool.

And why wouldn't one use this method to adjust the RECORD side of a tape 
deck...assuming the playback side is solidly calibrated?


Regards,

Mark Durenberger


----- Original Message ----- 
From: "Eric Jacobs" <Eric at NoopMedia.com>

> On Sunday, March 22, 2009 11:23 PM, William A. Brent wrote:
>>  but I was wondering - is there some reason to have recorded these 
>> "out-of-phase" in preparation for restoration?
>
> Absolutely.  If the transfer set-up allowed for adjusting the balance 
> control ahead of a mono mixer, the L-R channels could be nulled (cancelled 
> out perfectly) using the balance control in order to get the optimal mono 
> mix later after restoration.

> Naturally, after nulling the mono mix would have to be removed before 
> making the transfer, but at this point you know you have the L-R channel 
> balance set optimally for restoration work.
> At least this is the process I follow, and perhaps your person was doing 
> the same thing:
>
>   - reverse phase of one channel
>   - insert a mono mixer after a balance control or L-R trim
>   - mix to mono
>   - adjust/trim the L-R balance until L-R channels cancel each other out
>   - turn off the mono mix
>   - set the phase of the channels correctly (ie. undo phase reversal)
>   - playback and digitize
>
> If you do mix to mono (without correcting the phase) and you have near 
> silence, then your transfers were done correctly with the L-R channels 
> nicely balanced and nulled.
>
> Eric Jacobs
>