# Perceptual Characteristics of Voice Identification in Noisy Environments
## 2 Perceptual Characteristics in Different Noisy Environments  
### Experiment 1: Impact of Noise Type  
To investigate the influence of noise on the perception of voice identity, the ideal method is for the listener to listen to various auditory stimuli under various noise transmission conditions. However, the actual conditions are difficult to achieve. So, we recorded clear voices in the anechoic chamber and then added noise in the post-processing stage. The participants engaged in the listening experiment in the listening room.  
The pre-recorded voice was drawn from a pool of 10 clips of 5 female speakers. Each speaker read two sentences. All the voices were recorded in the anechoic room with a background noise level of below 20 dB and a reverberation time of below 0.1 s. The duration of each sentence was controlled to around 5 s. The microphone was located a fixed distance from the speaker's mouth. The pre-recorded voices were digitized at a sampling rate of 44.1 kHz.  
During the post-processing stage, the pre-recorded voices were combined with various noises and SNRs to simulate voices masked by different noise environments. The experimental signals were replayed to the participants using headphones in a quiet room. The sound pressure level (SPL) was 70 dB near the headphones. Figure 1 shows the experimental process of voice identity perception.  
(a) Noise Type and SNR  
White noise, pink noise, and speech noise were the three noise types used in the listening experiments. White noise is a kind of broadband noise that exists widely in communication systems, where the energy is uniformly distributed in linear coordinates. Pink noise is a typical occurrence in nature, and its energy decays by 3 dB each octave in logarithmic coordinates from low frequency to high frequency. The energy of speech noise is primarily concentrated in the low-frequency and medium-frequency bands. It is a background noise commonly present in public spaces. The spectrograms of the three types of noise are shown in Figure 2.  
According to prior research results [20], the SNRs of the listening experiment were selected from \(-8\) dB to \(16\) dB with a 2 dB or 4 dB increase. There were nine noise interference environments. Table 1 summarizes the SNRs used in the experiments. The selection of SNRs was the same in three types of noise environments to compare the results regarding voice identity perception. In total, ten pre-recorded sentences from five speakers were mixed with twenty-seven noise interference conditions. The voice signals masked by different noises were obtained.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline Serial number & \(1\) & \(2\) & \(3\) & \(4\) & \(5\) & \(6\) & \(7\) & \(8\) & \(9\) \\ \hline SNR (dB) & \(-8\) & \(-6\) & \(-4\) & \(-2\) & \(0\) & \(4\) & \(8\) & \(12\) & \(16\) \\ \hline \end{tabular}
\end{table}
Table 1: SNR selection in listening experiments.  
Figure 1: Experimental process of voice identity perception.  
Figure 2: Spectrograms of three types of noise. (**a**) White noise; (**b**) pink noise; (**c**) speech noise.  
Procedure  
Participants  
Twenty-six Mandarin speakers (age: 20.54 \(\pm\) 0.81 years) were recruited. All the participants reported no known hearing problems. During the hearing test, the barely noticeable difference (JND) of the loudness at 80 dB SPL is less than 2.5 dB. The JND of 1 kHz frequency is less than 10 Hz. Before the formal experiment, the participants took part in a simple pre-experiment to understand the experimental setup. A total of 10530 (26 participants \(\times\) 405 voice pairs = 10530) stimulus-response events occurred. To guarantee the reliability of the experiment, the Cronbach alpha values were calculated for all the data. The result shows that the experiment has good internal reliability (Cronbach's Alpha = 0.903, N = 26).