Locking To External Word Sync Inputs; Locking To External Aes Sync Inputs - Apogee AD-1000 Operating Manual

AD-1000 Operating Manual
Pull-Up and Pull-Down Sync
Two other positions of the SAMPLE RATE Selector provide the unique ability to increase or decrease the input
sampling rate by a 1.001 ratio. Utilizing the above settings, any WC (Word Clock/Sync) input will be multiplied
or divided by 1.001. For example a 44.056 kHz WC input will deliver 44.1 kHz locked to the input. Illumination
of the 44 LED indicates lock. Users tell us this feature has saved the day in situations where the wrong sample
rate was used.
The x1.001 and ÷1.001 positions are marked with a square ( ) which corresponds to the square on the WC,
AES, OPT AND S/P DIF sync source positions.
1.001 is the ratio between the frequency of a NTSC color signal and the original monochrome standard. When
engineers in the USA first developed the NTSC color television system, they found interference problems using
the same frequencies as the monochrome system they were replacing. The solution was to slightly shift the
color video frequency by 0.1% – thus the 1.001 ratio.
When Compact Discs (CDs) were developed, a reliable method to store the digital audio data in preparation for
making the CD was necessary. The solution was to use a video cassette recorder to store the wide bandwidth
information. A sampling rate of 44.1 kHz was chosen to pack the digital audio data conveniently on a U-matic
video cassette in the form of a video signal. The video signal chosen was the NTSC monochrome standard of
525 lines/60 frames per second (525/60). This CD 44.1 kHz sampling rate is not compatible with a NTSC color
video signal (525/59.94 Hz). In fact, 44.1kHz is 1.001 times higher than the 44.056 sampling rate that would be
compatible with NTSC video. Therefore to lock a 44.1kHz sampling rate to NTSC video requires multiplying the
NTSC reference by 1.001.
Digital video machines (D-1, D-2) use 48 kHz sampling locked to NTSC video or PAL video. F-1 type systems
use 44.056 Hz sampling in NTSC versions and 44.1 kHz sampling in PAL versions. As an example where you
would need to use ÷1.001: in a music video application, a picture running at 59.94 FPS has to sync with a CD
sound track running at 60 FPS (44.1 kHz sampling rate).
AES Sync Inputs
Selecting the AES sync source positions enables the AD-1000 to lock to any AES/EBU digital audio source. The
AES/EBU Sync Source is input via the BNC connector. No audio information is transferred unless a digital
input is selected. The sync information is extracted from the AES/EBU data stream. Two AES positions are avail-
able. The position labeled 110 AES terminates the input with a 110 impedance. You would use the
Terminated position if the AD-1000 was the last or the only device in the AES chain. The position with the ( )
above it signifies a bridged input of 5k for the AES. This position would be used if the AD-1000 was not the
last device in the chain.
Depending on the input sampling rate, the appropriate LED will illuminate to indicate lock. The SAMPLE RATE
Selector should be in the 6 o'clock position. In this sync source mode, the AD-1000 normally outputs the same
frequency as the AES Signal connected to the Sync Input. Two other positions of the SAMPLE RATE Selector
provide the unique ability to increase the input sampling rate by a 1.001 ratio. See the earlier section on Pull-
Up and Pull-Down for details.
S/PDIF Sync Input
Selecting the S/PDIF sync source position enables the AD-1000 to lock to S/PDIF digital audio sources. No
audio information is transferred unless the input selector is set to Digital. The sync information is extracted from
the S/PDIF data stream. Apply the S/PDIF input signal to the BNC. If you are not looping signal through to
another unit, terminate the signal by selecting the correct switch setting on the 8 position DIP switch located
on the top of the AD-1000. Additional details are on page 31. If looping the signal to other devices, the last
unit in the chain should be terminated with 75 .
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