# Dual-Mic Speech Enhancement Based on TF-GSC with Leakage Suppression and Signal Recovery
## 4 Experimental Results  
To evaluate the performance of the proposed method, the acoustic environments depicted in Figure 3 were simulated using the image method [35]. The dimension of the room was [6.7 m, 6.1 m, 2.9 m]. Two microphones were located at [3 m, 3 m, 1.5 m] and [3.14 m, 3 m, 1.5 m], respectively, 14 cm away from each other, which is typical for modern smartphones. The reverberation times (RT60s) were 300 ms and 500 ms. The distance between the desired source and the microphone array was 0.4 m, while that for the interfering source was 0.8 m. The DoA for the desired source was \(-90^{\circ}\), \(-60^{\circ}\), \(-30^{\circ}\), and \(0^{\circ}\) when \(0^{\circ}\) indicates the broadside direction, while the interfering source was located at [\(-90^{\circ}\), \(+90^{\circ}\)] with a \(30^{\circ}\) interval. Twenty utterances spoken by 13 male and 7 female speakers were selected randomly from the TIMIT database [36] as the desired speech signals. Babble, F16, and Factory1 noises from the NOISEX-92 database [37] and restaurant and street noises from the AURORA 2 database [38] were used as diffuse noise, which was constructed using the arbitrary noise field generator [39]. Five competing talker utterances were selected randomly from the TIMIT database as directional noises. The SNRs for diffuse or directional noise were 0, 5, 10, 15, and 20 dB. The sampling rate was 8 kHz and the 256 point STFT with a Tukey window was used with the frame shift of 160 samples. The empirically determined values of the parameters for the conventional TF-GSC with postfiltering [16] and the proposed one with two additional modules are summarized in Table 1. The ANC filter \(G\) and the noise reference power for ANC update \(P_{est}\) were converged before evaluating the performance. The parameters not included in the table were set to be the same as in [16], which produced the highest average performance. Perceptual evaluation of speech quality (PESQ) scores [40] were carried out to evaluate the performance. Figures 4 and 5 show the average PESQ scores and the 95% confidence intervals (CIs) for the input microphone signal, the output of the conventional TF-GSC with postfiltering, and the proposed scheme in diffuse noise environment according to the SNR, RT60, and the azimuth of the desired source averaged for five noise types. The conventional algorithm improved the PESQ scores in all conditions, but the improvement in performance reduced as the desired source moved from the broadside direction (\(0^{\circ}\)) to the end-fire direction (\(-90^{\circ}\)). The proposed leakage suppression and signal recovery were considered to be effective in maintaining the performance for all DoAs of the desired source. The improvement in performance over the conventional TF-GSC was statistically significant when the desired source was located near the end-fire direction (\(-90^{\circ}\) and \(-60^{\circ}\)) and the SNR  
Figure 2: Selected microphone signal to be used for signal recovery depending on the similarity differences between the microphone signals and the outputs of the FBF and BM. was higher than 0 dB, but was insignificant when the desired source was located at the broadside (0\({}^{\circ}\)). This may be because the steering error was smaller when the desired source was located in the broadside direction, and the signal recovery module essentially has no impact for the broadside as it just adds the scaled FBF output \((\mathbf{X_{1}}(n)+\mathbf{X_{2}}(n))/2\) to the FBF output. A similar tendency was observed for both RT60s. The PESQ score differences between the proposed and baseline beamformers for each noise type are shown in Figure 6. The proposed beamformer improved the PESQ scores in both stationary and nonstationary noise environments. The signal recovery module may work more effectively when the desired source is located in the end-fire direction by recovering the attenuated desired signal using the closer microphone signal.