Spatial Audio Processing: MPEG Surround and Other Applications

9.4 Using spatial audio decoders as mixers

Mixing is preferably applied to the transmitted sum signal (Equation 9.1) without explicit computation of ŝ_i(n). In this approach, the sum signal s(n) is directly transformed to a stereo or multi-channel output signal with the correct spatial attributes. A BCC synthesis stage or MPEG Surround decoder can be used for this purpose. In the following, a stereo reproduction case is considered, but all principles described can be applied for generation of multi-channel audio signals as well.

A stereo BCC synthesis scheme, applied for processing the sum signal (Equation 9.1), is shown in Figure 9.6. The scheme comprises a filterbank (FB), gains (g₁, g₂), delays (D₁, D₂), a decorrelation stage and inverse filterbanks (IFB). The purpose of this scheme is to generate a signal that is perceived similarly as the output signal of a mixer as shown in Figure 9.3. This requires correct synthesis of ICTD, ICLD, ICC and output levels of the BCC output as those obtained when the original source signals were directly fed in to the mixer (see Equation 9.2).

Figure 9.6 A mixer for generating stereo signals directly given the sum of a number of source signals without explicit computation of the source signals. Gain factors, delays, and decorrelation are applied independently in sub-bands.

The same side information as for the previously described more general ...