Spatial Audio Processing: MPEG Surround and Other Applications

7.3 Sound source position dependencies

7.3.1 Experimental procedure

In a first experiment, the aim was to determine the minimum number of parameter band basis functions required to represent the left and right HRTFs for a specified position to obtain a fully transparent representation of an HRTF pair.

As outlined in Section 7.2, Equation (7.1), the warp factor w directly influences the number of parameter bands used for describing the parameterized HRTF spectra. With an increase of w, the number of parameter bands decreases and hence the error or difference between original HRTF spectra and parameterized HRTF spectra will increase. In this subjective evaluation, the parameterized HRTF pair was compared with the original HRTF pair for the same location. During the experiment, the value of w was changed adaptively to determine a threshold value. This experiment was performed for both overlapping as well as nonoverlapping parameter bands.

Figure 7.3 Reconstructed (solid line) HRTF magnitude spectra (left-ear only) using overlapping parameter bands (top panel) or nonoverlapping bands (lower panel). The dotted lines indicate the original HRTF magnitude spectra.

Table 7.1 Elevation and azimuth (in degrees) for the nine positions under test.

A set of nine different spatial positions were ...