Inovonics JUSTIN 808, Инструкция по установке и эксплуатации

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The JUSTIN 808 maintains a long-term delay history for an in-
definite period so that trends may be analyzed over days,
weeks and months. See the Data Logging discussion on Page
24.
Delay
Correction
Options
Under
Setup
and
AES Au-
dio Adjustments
you will
find a host of switches
and sliders. The top
switch,
Enable Delay:
, sim-
ply turns
On
or
Off
the
JUSTIN 808 primary func-
tion of time-aligning the
analog FM and digital HD1
programs. At the bottom
of this screen are the
Airchain:
‘radio buttons’ to
assign the JUSTIN 808 to
the proper signal path, as
instructed on Page 13,
Step 3. Other controls are
covered in appropriate discussions.
The Delay
Correction Rate
As discussed in the Quick-Start Setup section, the factory-
default delay correction rate is a leisurely 50 samples per se-
cond. This means that a one-second time offset would take the
JUSTIN 808 a full fourteen minute s (!) to correct.
Again, this molasses-like default value is in deference to Niel-
sen’s Portable People Meter (PPM), a widely-used system for au-
diting a listening audience to determine market share. The PPM
depends on a subliminal family of audio tones buried in, and
masked by, program content. Any change in the frequency of
these tones renders the system useless.
The JUSTIN 808 corrects for FM-to-HD1 misalignment by slowly
moving the audio in time. This creates a frequency shift, much
as a moving train whistle demonstrates a Doppler shift. Musi-
cally-trained individuals are said to be able to resolve a pitch
shift of 2Hz. At 440Hz (musical ‘A’), a delay correction rate of
200 samples per second (sps) might be audible to a select few
listeners. But the Nielsen PPM is even more sensitive than this
and requires a correction rate something under 100sps.
The factory-default value of 50sps can be considered uncondi-
tionally safe, but will take a good long while to correct signifi-
cant errors. In actual operation, once the FM and HD1 timing
error has been brought to zero, whatever mechanisms are re-
sponsible for causing the timing to wander are typically very-
long-term, and a correction rate of 50sps should keep the error
within the ±3 sample limit suggested by iBiquity Digital Corp.