Lexicon CP-1 User Manual download pdf (Page 42)

Lexicon

Page 38

the left speaker.

The main problem with a first-order device is that the subtracting signal is

also heard by the opposite ear. In our example, the canceling signal from the

right loudspeaker will diffract around the head to the left ear, interfering

with the left-speaker sound and producing a “comb filter” which colors the

sound in an obvious and unpleasant way. Furthermore, the listener’s head

is not well represented by a simple delay line. Both the delay and the

amplitude of the opposite-ear sound vary in complicated ways with fre-

Theory

and

Design

The Panorama

Program

Loudspeakers placed on either side of the listening position are the most

effective and foolproof way to produce added Spatial Impression. Since it

is not always possible to have side loudspeakers, the CP-1 uses crosstalk

elimination to simulate them when they can’t physically be there. In

Panorama the front speakers are driven entirely by the front digital outputs

of the CP-1. (Panorama disables any side speakers present, and simulates

them electronically.)

Versions of the Atal/Schroeder/Damaske/Mellert technique mentioned

earlier have appeared in several consumer signal processors under various

trade names, as well as in a line of loudspeakers that achieved a similar effect

acoustically. These have all been what we call “first-order” devices. To see

what this means, imagine there is a sound coming from the left channel only.

This sound will travel to the left ear of the listener, then diffract around the

listener’s head and be heard by the right ear. If we take the left-channel

sound, delay it just the right amount, invert it in phase and feed it to the right

speaker, it will arrive at the right ear just in time to cancel the crosstalk from

Sound from speaker L travels to the

left ear and also to the right ear, a

time ∆ t later.

If we supply a negative delayed sig-

nal to the right speaker, this crosstalk

can be canceled.

Imagine a click in the left speaker...

Input

Sound

Speaker

Level

First order

Correction

Speaker

Level

L R

+ ∆ t

1 2 ... 37 38 39 40 41 42 43 44 45 46 47 ... 57 58

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Lexicon CP-1 User Manual Page 42

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