pat@decwrl.dec.com (Pat Powers) (11/05/90)
Quite right, the choice is between stereo imaging with difference in loudness between the channels only, or both loudness and timing. The trouble with allowing timing difference between the channels is that there is phase cancelation. Superimposing the same signal on itself with a slight delay gives in peaks and valleys in the frequency response, resulting in a harsh, thin sound. You can get a feel of this effect by listening through a tube to get extreme phasing. Recording engineers spend quite a bit of their time avoiding phase cancellation owing to leakage between microphones, reflections off walls and other surfaces, etc. etc. Phase cancellation is particularly a problem when playing back over mono sources, still common in radio. Another problem with allowing phase difference between channels is that there is little control over the user's playback equipment. How far apart are the speakers, or maybe he is using headphones? And the size of the room and location of the walls is bound to be different. All this being as it may, if you can accept the disadvantages, music with phase differential between the channels can give superior depth of field and natural 3-D sound. Let me share a story with you. I was visiting a girl friend in Boston and we accidentally left her stereo JVC blaster on record as we walked about the place and talked. Eventually we noticed and played it back. It was amazing! it sounded so real, true 3-D motion, you could practically point to the spot each voice was coming from. The secret was that the microphones were very close to the speakers and we did not move the deck so the playback was in exactly the same room, exactly the same spot to give extremely realistic 3D imaging.