Subframe Delay; About Transmission Levels And Metering; Meters - Orban OPTIMOD 6300 Operating Manual

OPTIMOD 6300 DIGITAL
or 96 kHz. These rates can be synchronized to the 6300's internal clock, its AES3 digi-
tal input, its AES11id input, or its wordclock input.
We expect that transmitters that transmit sample rates below 32 kHz will provide
internal sample rate conversion, and that most will probably accept audio at 48 kHz
sample rate regardless of the final sample rate of the transmission. Any sample rate
conversion may cause the transmitted sample to become asynchronous to the peak-
controlled samples emerging from OPTIMOD 6300 and may therefore introduce
overshoot. Fortunately, as the audio bandwidth becomes lower, this becomes less of
the problem because the 48 kHz sample rate within OPTIMOD 6300 oversamples the
audio. It is therefore less likely that peaks will "slip between the samples."

Subframe Delay

OPTIMOD 6300 provides an adjustable time delay of up to 96 milliseconds. This al-
lows the installer to force the total delay through the processing to equal one frame
(in sound-for-picture applications). The definition of "frame" depends on the system
in which OPTIMOD 6300 is installed.
The selections are
monochrome video), 29.97 fps (NTSC color video), 25 fps (most PAL
video), and 24 fps (film). You can also adjust the delay in one-millisecond
increments from 15 to 96 ms.

About Transmission Levels and Metering

Meters

Studio engineers and transmission engineers consider audio levels and their meas-
urements differently, so they typically use different methods of metering to monitor
these levels. The VU meter is an average-responding meter (measuring the approxi-
mate RMS level) with a 300ms rise time and decay time; the VU indication usually
under-indicates the true peak level by 8 to 14dB. The Peak Program Meter (PPM) in-
dicates a level between RMS and the actual peak. The PPM has an attack time of
10ms, slow enough to cause the meter to ignore narrow peaks and under-indicate
the true peak level by 5 dB or more. The absolute peak-sensing meter or LED indica-
tor shows the true peak level. It has an instantaneous attack time, and a release
time slow enough to allow the engineer to read the peak level easily. Figure 1-1
shows the relative difference between the absolute peak level, and the indications
of a VU meter and a PPM for a few seconds of music program.
M (approximately 24 ms delay), 30 fps (NTSC
INIMUM
1-17
INTRODUCTION