Stereo upmixing began with sum-and-difference signal processing decades ago

Evidence

Such processing converts the phase or time delays between the loudspeakers at low frequencies to a perception of level differences between the ears, and at high frequencies the perception remains as a time difference in the signal between the ears. This effect makes the virtual source direction depend on the signal itself (Cooper, 1987; Lipshitz, 1986). The produced binaural cues vary with frequency, and different cues suggest different directions for virtual sources (Pulkki, 2001b). The cue may thus generate a ‘spread’ perception of the direction of sound, which is desirable in some cases. The effect is also dependent on listening position. For example, if the sound signal is delayed by 1 ms in one loudspeaker, the listener can compensate for the delay by moving a bit towards the delayed loudspeaker. Time delay panning thus resembles spaced microphone techniques, since the spacing between the microphones causes time delays between microphone signals and since the resulting spatial image is similar. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1911 (#expands, via linked claim)

Categorization

• XREF: connects to: Stereo principles were understood decades before they were commercialized, and cinema drove their adoption; Stereo loudspeakers create directional illusion through summed phase shifts mimicking time delays — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1911

Broader Connections

• Stereo loudspeakers create directional illusion through summed phase shifts mimicking time delays #expands (0.75) — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1911