Finger snaps

To understand how stereo's phantom third channel is produced there is a simple experiment you can perform. In a quiet room close your eyes, put your hand at arm's length - centered with your nose - and snap your fingers. Note how the sound is localized perfectly. Continue snapping and move to the extreme left, then right. Again, proper localization occurs. This is the ear/brain localization mechanism we share with many higher order creatures, developed over millions of years of evolutionary growth. This localization skill coupled with peripheral vision, and superior pattern recognition (lower order animals can't recognize stationary patterns as well as we can) helped humans from becoming dinner. Today this localization skill can be leveraged to produce the illusion of a three dimensional soundstage without a physical third speaker. When you listen to your system and hear a singer, dead center and behind the loudspeakers, there are two things you know without further study. First, you know the singer's voice has been recorded at equal levels between left and right speakers. This is known as monaural (one sound), though it is really two sounds, of equal value, in a stereo setup. Secondly, you know the singer's voice is not without reflections. Reflections of voice can come from the room the singer is in, or from artificially delayed copies of the voice, electronically added. Both conditions are called reverberation (persistence of sound after the original sound stops), or reverb for short, and it is this reverb that helps the voice have depth, or space. A great example of this can be found on one of Stereophile's test discs. I believe it was disc number two where track 10 had soundstage mapping. If memory serves correctly two microphones were used to convey a single person walking forward and backwards, left and right, closer and further from the microphone and it was excellent for depth recreation and localization. As the speaker moves away from the microphone and to the back of the room, he appears far behind and unattached to either loudspeaker. This is on a properly setup system and the subject of where we're going over the next few days. To understand this better, we will focus first on the monaural aspects, second the reverb.