Spatial Audio Processing: MPEG Surround and Other Applications

9.2 Motivation and details

As mentioned above, the scheme for joint-coding of audio source signals, shown in Figure 9.2, is based on transmission of the sum of the audio source signals,

where M is the number of source signals and s_i(n) are the individual source signals.

Similar to spatial audio coding techniques, this method relies on the assumption that the perceived auditory spatial image is largely determined by the inter-channel time difference (ICTD), inter-channel level difference (ICLD), and inter-channel coherence (ICC) between the rendered audio channels. Therefore, as opposed to requiring ‘clean’ source signals s_i(n) as mixer input in Figure 9.1, only signals ŝ_i(n) are required that result in similar ICTD, ICLD, and ICC at the mixer output as for the case of supplying the real source signals s_i(n) to the mixer. There are three goals for the generation of ŝ_i(n):

• If ŝ_i(n) are supplied to a mixer, the mixer output channels will have approximately the same spatial cues (ICLD, ICTD, ICC) as if s_i(n) were supplied to the mixer.
• ŝ_i(n) are to be generated with as little as possible information about the original source signals s_i(n) (because the goal is to have low bitrate side information).
• ŝ_i(n) are generated from the transmitted sum signal s(n) such that a minimum amount of signal distortion is introduced.

Figure 9.3 A mixer for generating stereo signals given a number of ...