Optimisation of Bandwidth Allocation Strategy
Besides a psychoacoustically hierarchical transform, the choice of an appropriate strategy for bandwidth allocation across eigenchannels is also essential from the point of view of the resultant audio quality in KLT-based HBL. Aa listening test was conducted to find the optimal bandwidth allocation strategy for KLT-based HBL for 3/2 stereo format: an optimal combination of bandwidths for individual eigenchannels that achieve the best audio quality when the sum of these bandwidths is fixed. The optimisation of BAS was identified via three steps. Firstly, the data describing audio quality degradations caused by HBL using different bandwidth allocation strategies were collected thorough a listening test, see Figure 1.
Figure 1: Basic Audio Quality for different Bandwidth Allocation Strategies (40 kHz)
Based on these data, the mathematical relationship between audio quality and the bandwidth allocation strategies was established by means of regression modelling, see Figure 2.
Figure 2: Scatter plot of the basic audio quality predicted scores as a function of the actual scores obtained from the listening test (40 kHz)
Then, the optimal BAS that resulted in best audio quality was identified using a standard optimization technique, see Figure 3.
Figure 3: Response surface plot(40 kHz)
As a result, when the overall bandwidth was limited to 40 kHz, the predicted optimum bandwidth limitation strategy in the KLT domain was [18.0, 14.0, 4.0, 4.0, 0] kHz; while when the available overall bandwidth was restricted to 60 kHz, the predicted optimum bandwidth limitation strategy was [19.0, 16.5, 16.5, 4.0, 4.0] kHz.
This work is reported in detail in [P5].