Model 737 Soundtrack Loudness Meter - Leq(m) Operation and Features
2-8
Notes:
The null circuit has two points of transition (at 82 and 85), so the + and - LEDs
should be used in conjunction with the numerical display to set the correct levels
for that input.
Since the null points are only at 82 and 85, to align to 88, reduce the test tone
level to exactly 3 dB below Dolby Level and align to a null point at 85.
The window of equal illumination is designed to be extremely narrow, which
yields an accurate level setting when both LEDs are on, albeit dimly (the gain
error is less than 0.1 dB).
4. Unplug the calibrated input and repeat the calibration procedure for all other
input channels, one at a time.
5. As a final check, plug in all inputs and send the appropriate tone to all applicable
channels. The meter should register an Leq(m) value of:
88 - Dolby (Lt/Rt)
91 - Dolby Digital, Dolby SR (Lt/Rt), and Dolby (LCRS) soundtracks
94 - Dolby SR (LCRS)
6. Repeat the calibration if there is a significant discrepancy.
Note: The 3 dB difference between L, C, R and the surround channels matches the
transfer levels for Dolby Digital movie soundtracks.
2.3.7 Automated Input Adapter Board (Cat. No. 448B)An additional input adapter board is available for UK-type installations that provides
channel switching and level calibration specific to the format under measurement.
The card follows a logic source from either a Dolby Cinema processor (i.e., CP65),
the DS4-E mkII (UK), or a custom control to switch between formats. Re-calibration
and re-plugging is then avoided except for normal periodic alignment checks
(see Chapter 3 – Cat. No. 448B Input Adapter Board).
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