Operation 13
Operation 3
3.1. General
Outside of manually setting the peak hold function desired, operation of the
DLM is automatic. Because the AES/EBU standard requires format
information to be embedded within the data frame, the DLM contains
circuitry to automatically match its configuration to the format detected.
This means that consumer 16-bit or professional 24-bit digital audio formats
having sampling rates of 32 kHz, 44.1 kHz, or 48 kHz, are automatically
detected and correctly displayed on the DLM (patent pending).
3.2. Digital Headroom and The Crash Point
Overrange indication occurs when the input signal reaches a level just
slightly above the maximum allowed input level. When this happens, the top
three LEDs (0, -1, and -2) all change color to red while tracking the program
material peaks.
Overrange indication is set at the factory to occur at the point one count over
the maximum signal level (the maximum level is the point at which the
signal becomes all binary 1’s).
Note:
This point can alternately be set to 4 counts over the maximum signal level
by moving a jumper.
Practically, when you see the overrange indication occur, the offending
peak was .0008 dB below the maximum signal input level allowed by the
AES/EBU format (24-bit). Consult the documentation for the digital
equipment you are monitoring to determine the point at which the
manufacturer expects overrange indication to occur.
How a particular equipment deals with a level that hits the crash point may
be another consideration in determining the overrange trigger point, and
maximum operating peak level. Some equipment types are more tolerant of
input level “crashes” than others (i.e., one equipment may hold at all 1’s,
while another may rollover to all 0’s). In this example, the latter equipment
requires special monitoring attention.
3.3. The Peak Hold Switch
Both the model 280 and 380 provide three types of peak hold functions:
normal operation (3-second peak hold), indefinite peak hold, and peak hold
disabled. These function are selected through a three-position toggle switch
(supplied). Alternately, if operation of only one of these functions is desired,
the function can be selected by moving a jumper on the DLM main circuit
board.
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