8.1 DIGITAL DELAY APPLICATIONS AND USE.
This section goes beyond the typical operating guide that
only explains the front and back panel adjustments of a piece of equipment. Instead, we discuss
the basic acoustical concepts needed to get the most out of the use of digital delay in sound
systems. If you are familiar with these principles, feel free to skip ahead. Some principles may
require additional delay channels and options available with the Sabine DQX-206.
Why Digital Delays? The most intelligible sound occurs when two people speak face to face.
The sound is loud and dry, and the direction of the sound aligns with the speaker. The most
intelligible sound systems are the ones that come closest to emulating face to face communica-
tion. If this is your goal, a digital delay is essential to your sound system.
There are three distinct applications for digital delays. The first and most important is synchroni-
zation of the loudspeakers to control excess reverberation and echo. Second, digital delays
help control comb filter distortion, and finally, digital delays are useful for aligning the acous-
tic image so the direction of the sound seems to be coming from the performer rather than from
the loudspeaker.
Loudspeaker Synchronization
Sound travels at about 1,130 feet per second in air, or about 1 foot per millisecond. On the other
hand, electronic signals travel almost one million times faster through your sound system to the
loudspeakers. The main task for digital delays is to synchronize multiple loudspeakers so the
sound traveling different distances arrives at the listener’s ears at about the same time. Synchro-
nizing the loudspeakers reduces reverberation and echoes for improved intelligibility.
How to Synchronize Your Signals
There are several powerful tools available for precisely measuring the time a loudspeaker signal
takes to arrive at a certain point in the audience. Most of these tools are very sophisticated and
tend to be quite expensive. Fortunately, simpler tools are sufficient for most applications.
In the 1930’s, engineers synchronized the low and high frequency speakers in movie theaters by
feeding a sharp click through the system. They moved the speakers until they could only hear a
single sharp click coming from both speakers. You can use this same method with a common
child’s toy called a clicker. Pressing the thin metal strip makes a loud sharp click. A clicker is
especially useful when synchronizing the direct sound from the performer with the sound from the
loudspeakers.
Alternatively, you can use a phase checker especially for synchronizing the signals of two loud-
speakers (either LF and HF or two full range systems) since most of the phase checkers include a
click generator and receiver. Phase checkers are quite affordable and have other uses besides
synchronization.
Processing (or Group) Delays
Converting signals back and forth from the analog to digital domain always delays the signal a
little. These conversion delays are often called processing (or group) delays, and usually range
between 0.9 and 5 milliseconds. You will notice that Sabine delays always display the processing
delay as the smallest possible delay value. For the POWER-Q, the processing delay is 1.38
milliseconds. You can bypass the unit for 0 seconds delay.
Not all manufacturers acknowledge processing delays in their specifications, but you
must take
them into account when synchronizing your system. Make sure all digital equipment is on and not
bypassed when synchronizing. Also, be careful to make an appropriate adjustment in your delay
lines if you later add any type of digital equipment to the system.
Section 8: Using the POWER-Q Digital Delay
Section 8: Digital Delay
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