Delay time for speaker channels? [Archive]

jrobbo

27-02-2004, 10:05 PM

On Fri, 27 Feb 2004 20:34:25 +1100, John Gift <whatgift@hotmail.com>
wrote:

>I have this function on my Surround amplifier that allows me to adjust
>the delay time for the centre and rear speaker channels while using
>Dolby Digital.
>
>What I want to know is, exactly what does this do?
>
>Any help would be appreciated.

From the Dolby Pro Logic White Paper, at
http://www.dolby.com/tech/whtppr.html

"Time delay ensures that any front channel sounds that happen to leak
from the surround speakers will arrive at the listener just after the
front channel sounds. This will help prevent the leakage from pulling
the sound image away from the screen. Such leakage may be caused by
phase or amplitude differences present in the input signals caused by
azimuth misalignment or frequency response errors, or simple balance
errors in the stereo program."

and

"Time delay is often used to create an echo effect, which can help
give music reproduction a feeling of greater spaciousness. However,
that is not why it is used in Dolby Surround decoders. The real reason
is to improve the sense of clarity and directionality of front channel
sounds. This is done by taking advantage of the "Haas" or precedence
effect, which enables the main frontal sound to arrive at your ears
before the surround sounds. The time delay stage compensates for the
travel time of sound through the air, which takes about 1 millisecond
per foot distance. By knowing how far the listening position is from
the front and the surround speakers, it is possible to adjust the time
delay for optimal results.

There are generally two kinds of time delay available in Dolby
Surround products: adjustable, or unadjustable (fixed delay). As would
be expected, the adjustable delay allows a wider range of distances to
be used than the fixed delay."

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