Spatial Audio Processing: MPEG Surround and Other Applications

4.5 Subjective performance

Although the subjective quality of a BCC scheme may depend on several design choices in the analysis and synthesis stages, as well as the choice of the mono coder, the fact that a parametric model for spatial properties is employed results in two generic, typical observations.

• The subjective quality at low bitrates (typically 12–48 kbps for stereo audio content) for BCC-enabled coders is typically significantly higher than conventional stereo or multi-channel coders.
• With increasing parameter bitrate, the subjective quality saturates at a high, but not fully transparent level due to the limitations of the underlying parametric model.

Figure 4.10 Typical performance of a BCC-enhanced coder (solid line) in comparison with a conventional stereo coder (dashed line).

The typical performance characteristic for stereo content and a comparison with a conventional stereo coder is shown in Fig. 4.10. At bitrates below a certain point (in this example about 48 kbit/s) the BCC-enhanced coder outperforms the conventional stereo coder in terms of quality. For higher bitrates, however, the quality for the BCC-enhanced coder tends to saturate. The saturation results from the fact that BCC only restores statistical properties of the signals, and does not guarantee a full decoder-side waveform reconstruction. This quality limitation can be resolved by employing the concept ...