Spatial Audio Processing: MPEG Surround and Other Applications

4.2 Related techniques

4.2.1 Pseudostereophonic processes

BCC relies on a synthesis technique which can generate stereo and multi-channel signals given a mono signal. There is a long history of techniques attempting to ‘enhance’ mono signals to create a spatial impression, i.e. to generate a signal pair or more channels evoking some kind of spatial impression. Such techniques are often called ‘pseudostereophonic’ processes. Janovsky [151] proposed a scheme where a lowpass filtered version of the mono signal is given to one loudspeaker and a highpass filtered version to the other loudspeaker. Another technique uses complementary comb filters for generating left and right signals [179]. Schroeder [232] proposed the use of allpass filters instead of comb filters resulting in a stereo effect with less coloration artifacts. The use of a reverberation chamber with one loudspeaker emitting the mono signal and two microphones generating left and right signals was described by Schroeder [231] and Lochner and Keet [184]. Another scheme gives the mono signal to both loudspeakers and adds an attenuated and delayed version of the mono signal to one loudspeaker and the same phase-inverted attenuated and delayed signal to the other loudspeaker [179, 180]. Enkl [80] proposed the use of time-variant controllable filters controlled by properties of the mono signal. A more thorough review on these pseudosterephonic processes is given in [26].

In all these techniques, the spatial distribution of the ...