## 2 Objective Evaluation Test
### Perception Test  
Criterion: The stereo-to-multichannel upmix should generate a high subjectively perceived spatial quality. This is accompanied with the result that the listening experience is improved compared to the initial stereo configuration, and that the listener feels projected in the middle of the sound events. The procedure of the perception test is shown in Figure 12. The test signal is identically equal to the test signal of the volume and phase test and is used as input signal for the tested upmix. The interaural cross-correlation coefficient (IACC) describes the subjectively perceived spatial quality of sound events, and is a measure for apparent source width (ASW). The lateral energy fraction (LF) describes the impression of spatial quality, and is also a measure for listener envelopment (LEV) [7; 19; 20]. For the determination of IACC, the generated upmix output signals \(x_{FL}\), \(x_{C}\), \(x_{FR}\), \(x_{SL}\) and \(x_{SR}\) are used to create a simulated sound field on the basis of head-related impulse responses (HRIR). The binaural signals:  
\[ \begin{array}{l}p_{L}(n)=\sum\limits_{i}x_{i}(n)*h_{i,L}(n)\\ p_{R}(n)=\sum\limits_{i}x_{i}(n)*h_{i,R}(n)\end{array}  \tag{13}\]  
result from the summed generated upmix output signals \(x_{i}\) across all channels \(i\) of the multichannel configuration convolved with the particular head-related impulse responses \(h_{i,L}\) and \(h_{i,R}\) for the left and right ear (with \(i\in I\) and \(I=\{FL,\ C,\ FR,\ SL,\ SR\}\)). IACC results from the normalized cross-correlation of the half-wave rectified and with a third-order Butterworth filter (\(f_{c}=1\) kHz) low-pass filtered binaural signals \(p_{L}\) and \(p_{R}\). The prefiltering ensures that the results correspond better to the subjectively perceived spatial quality [21; 22; 23]. For the determination of LF, the generated upmix output signals \(x_{FL}\), \(x_{C}\), \(x_{FR}\), \(x_{SL}\) and \(x_{SR}\) are used to create another simulated sound field. The signal \(p_{0}\), which is recorded from a virtual omnidirectional microphone, results from the summed generated upmix output signals \(x_{i}\) across all channels \(i\) of the multichannel configuration, and is given by  
\[p_{0}(n)=\sum\limits_{i}x_{i}(n) \tag{14}\]  
The signal \(p_{8}\), which is recorded by a virtual bidirectional microphone, results from the summed generated upmix output signals \(x_{i}\) across all channels \(i\) of the multichannel configuration weighted with the respective loudspeaker directions \(\varphi_{i}\), and can be written as  
\[p_{8}(n)=\sum\limits_{i}x_{i}(n)\cdot cos(\varphi_{i}) \tag{15}\]  
Figure 12: Block diagram: Perception test. IACC: interaural cross-correlation coefficient; LF; lateral energy fraction; LP: low-pass. LF results, with the signals \(p_{8}\) and \(p_{0}\), from the ratio of acoustic waves, which are arriving at the listening position laterally and from all directions [7; 23], given by  
\[LF=\frac{\sum_{n=1}^{N}p_{8}^{2}(n)}{\sum_{n=1}^{N}p_{0}^{2}(n)} \tag{16}\]  
Due to using a simulated sound field, the differentiation between early-and late-arriving signal components is omitted [7]. The evaluation score of the perception test based on IACC results in  
\[score_{WT1}=1-IACC \tag{17}\]  
and is a direct measure for ASW. The subjectively perceived spatial quality is the higher, the lower IACC is. The evaluation score \(score_{WT2}\) of the perception test based on LF results in  
\[score_{WT2}=LF \tag{18}\]  
and is a direct measure for LEV. The impression of spatial quality is the higher, the higher LF is.