Setting The System Reference; Time Code Chase Operation - Alesis AI-2 Reference Manual

The AI-2 determines a sample rate ratio from the frame rate and
sample rate options selected in the reference menu. The actual
time code position is then calculated by subtracting the AI-2 offset
from the ADAT tape position determined using this sample rate
ratio.
From this it can be seen that when either the sample rate or frame
rate is changed, the sample rate ratio and therefore the tape time
code position will change. As an example, if the AI-2 sample rate is
altered to 44.100 KHz at 30 fps then the sample rate ratio becomes
1470, and the ADAT time code position would now advance one
frame for every 1470 samples instead of one frame for every 1600
samples as above.
The AI-2 provides a number of different sample rate frequency
options, including 0.1% pull up and pull down rates to allow the user
to correct, transfer or synchronization problems. An inadvertent
sample rate change from 48 K to 44.1 K is drastic and extremely
noticeable and could not be made by mistake, however the 0.1%
sample rate options are not nearly as noticeable and should be
used with caution.
When operating in a 30 or 29.97 frame based system the AI-2 time
code type can be either DF or NDF as required to suit a particular
application. Consideration need only be given to normal tape
synchronization issues, such as operating with mixed code types.

4.3 SETTING THE SYSTEM REFERENCE

Before using the system, decide what system speed reference the
ADATs will be locked to. The AI-2 should be referenced to the
same source that the other transports in the system are referenced
to. The AI-2 default reference is automatically determined by the
control mode. Under normal circumstances it should not be
necessary to change this. If a different reference source is
required, press SETUP and then the MENU key until the reference
menu is displayed. Use the DOWN and UP keys to select the
required reference.

4.4 TIME CODE CHASE OPERATION

Time code chase operation can be used as a quick test check that
the AI-2 is operating correctly. When there is no controller
connected the AI-2 will automatically switch to time code chase
mode.
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