Theory and Design
Lexicon
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
Imagine a click in the left speaker...
Sound from speaker L travels to the left ear and also to the right ear, a time Δ t later.
If we supply a negative delayed sig- nal to the right speaker, this crosstalk can be canceled.
Speaker | Input | Speaker | First order |
Level | Sound | Level | Correction |
L | | R | |
| to | t | t + Δ t |
| | o | o |
| L | R | |
| L | R | |
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-