Model 737 Soundtrack Loudness Meter - Leq(m)
2-1
Chapter 2Operation and Features
The Model 737 Soundtrack Loudness Meter – Leq(m) is a simple 1U, rack-mountable
device that measures the equivalent loudness of one-, two-, four-, or six-channel inputs,
typically from the non-equalized outputs of a cinema processor or mixing console.
Since the time available for averaging is several hours, a soundtrack can be evaluated
in small sections or in its entirety. The current Leq(m) value is displayed in the LED
window. The circuit consists of a set of six input stages, five CCIR (2K) filters, five
square law detectors, and a display driver that takes the average of the squared signal
voltage and then extracts the square root/log of the resultant DC signal. A separately
processed average DC circuit outputs a signal that is buffered for use with a chart recorder/
moving coil meter for trend analysis.
The Trip Set adjustment sets the level that lights the Tr ip LE D and triggers a signal
to the Trip Output. The Trip Output can activate a more noticeable device (such as
a light or sound) to alert the user that a preset level has been exceeded at the end of
the measurement.

2.1 Front Panel Controls

The front panel has three pushbuttons (Cal, Start, Stop), a two-digit LED that displays
the current Leq(m) value, a screwdriver-accessible hex switch to set the trip level, trim-
pots for the six analog inputs, and a 6/4 – 2 channel switch.
Figure 2-1 Model 737 front panel
The right side of the front panel is shown in detail below.
Figure 2-2 Detail of front panel controls
C
4
5
6
7
8
9
A
B
C
D
E
F
0
1
2
3
26/4-
85
Leq(m)
Trip
Trip
Set
-
+
Cal Start Stop
LCRLsRs Sw Mon
Model737
SoundtrackLoudness Meter -- Leq (m)
C
4
5
6
7
8
9
A
B
C
D
E
F
0
1
2
3
26/4-
Trip
Trip
Set
-
+
Cal Start Stop
LCRLs Rs Sw Mon
Set
Cal Start Stop

Cal

Start Trip Set

Stop Audio Input Trimpots

6/4 - 2 channel switch

Mon Out Trimpot

Calibration LEDs

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