Hall Research AD-340 - Manual (Page 17)

Universal Audio Delay Processor
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External (Acoustic) Delay: The need to adjust for external delay becomes an
issue when the listener gets the same sound from different sources (speaker
sets) that are placed at different distances to the listener. The bigger the relative
distance between the speaker sets the more annoying. External delay is caused
by the speed of sound; because the sound from speaker systems located at
different distances arrive at different times. Speed of sound is a function of air
temperature. At the standard air temperature of 72 °F (23°C) the speed of sound
is 1130 feet/second (345 meters/second), or 1.13 feet/msec (0.345
meters/msec). The speed of sound increases with a rise in temperature and
decreases with a fall in temperature.
The AD-340 Audio Delay Processor is designed to provide a flexible way to
adjust for these types of delay by adding a digital delay function based on 5
different delay types.
Delay Type Delay Function
Millisecond The audio will be delayed by the number of milliseconds
Frames – 50 Hz The audio will be delayed by the number of Video Frames
Frames – 60Hz The audio will be delayed by the number of Video Frames
Feet Find the distance between the direct sound source (main
speaker set near the stage) and the delayed sound
source (speaker set closest to the listener) in feet.
The audio will be delayed by the calculated number of
milliseconds corresponding to the distance in feet and the
speed of sound (at the given temperature).
Meter Find the distance between the direct sound source (main
speaker set near the stage) and the delayed sound
source (speaker set closest to the listener) in meters.
The audio will be delayed by the calculated number of
milliseconds corresponding to the distance in feet and the
speed of sound (at the given temperature).
(50 FPS = 20 ms per video frame, 60 FPS = 16.67 ms per video frame)