[ProAudio] FeralA - Recordings released encoded with Dolby A

[John Chester]

On 2/11/20 1:52 PM, Bob Katz wrote:

> Dear John:
>
> In other words, in Plangent, first you adjust the angle of the repro 
> head to get the best bias recovery --- which should match the angle of 
> the record head. BUT, due to several factors, including possible gap 
> scatter (non-colinear gaps), this might not fix the time delay between 
> the two channels.
>
> If I was doing an analog tape transfer of this recording, if I had 
> access to the bias signal like you that's what I'd use to adjust the 
> angle of the repro head. In the absence of that I listen and do my best.
>

If there are tones, and we trust them, time difference can be determined 
from the tones.  I can of course get a pretty good idea about whether 
the tones match the music by looking at the bias frequency and flutter 
profile.  On an album master, where some cuts were mixed at different 
times or maybe even in different studios, it's common to find that the 
tones match some cuts but not others.  As others have pointed out, 
sometimes the tones don't match any of the music.

If there are no tones, or we don't trust them, sometimes an accurate 
measurement can be obtained by an "azimuth" measurement tool like the 
one in Izotope RX.  It does show a "stability" number, which indicates 
how sure it is of its result.  It works quite well on material that has 
a strong center channel, and listening tests confirm that using its 
recommended time adjustment sounds better.  On other material it is not 
to be trusted.  If the "stability" number is low or the recommended 
adjustment is complete nonsense, the best answer for us is to leave well 
enough alone.  As you point out, the mastering engineer can and should 
check for problems, and adjust if needed.

Time adjustment is done in integral sample steps, so no additional 
processing of the audio is required.

We have found that when listening to material with a well-defined stereo 
sound stage, correct time adjustment is much more obvious on the 
defluttered audio.  When inter-channel time adjustment of a stereo 
recording is correct, the sound stage will suddenly snap into focus.  
When listening to the audio which has flutter, the same adjustment 
produces only a slight improvement, and I'd have a hard time choosing 
the correct adjustment just by listening.

-- John Chester