## 4 Construction of a Timbre Perception Feature Model
### Construction of the Objective Acoustic Parameter Set  
Timbre is a multidimensional perception attribute that is closely related to the time-domain waveform and spectral structure of sound [60]. In order to establish a timbre perception feature model, an objective acoustic parameter set was constructed using 54 parameters extracted from the timbre database. Objective acoustic parameters refer to any values acquired using a mathematical model representing a normal sound signal in the time and frequency domains. These 54 parameters can be divided into 6 categories [61]:  
1. _Temporal shape features_: calculated from the waveform or the signal energy envelope (e.g., attack-time, temporal increase or decrease, and effective duration).
2. _Temporal features_: auto-correlation coefficients with a zero-crossing rate.
3. _Energy features_: referring to various energy content in the signal (i.e., global energy, harmonic energy, or noise energy).
4. _Spectral shape features_: calculated from the short-time Fourier transform (STFT) of the signal (e.g., centroid, spread, skewness, kurtosis, slope, roll-off frequency, or Mel-frequency cepstral coefficients).
5. _Harmonic features_: calculated using sinusoidal harmonic modeling of the signal (e.g., harmonic/noise ratio, odd-to-even and tristimulus harmonic energy ratio, and harmonic deviation).
6. _Perceptual features_: calculated using a model of human hearing (i.e., relative specific loudness, sharpness, and spread).  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & **Bright** & **Dark** & **Sharp** & **Vigorous** & **Raspy** & **Coarse** & **Hoarse** & **Consonant** & **Mellow** & **Pure** \\ \hline Bright & 1.00 & \(-\)0.99 & 0.90 & \(-\)0.93 & 0.24 & \(-\)0.48 & \(-\)0.31 & 0.13 & \(-\)0.27 & 0.47 \\ Dark & \(-\)0.99 & 1.00 & \(-\)0.89 & 0.93 & \(-\)0.20 & 0.49 & 0.33 & \(-\)0.17 & 0.26 & \(-\)0.48 \\ Sharp & 0.90 & \(-\)0.89 & 1.00 & \(-\)0.93 & 0.58 & \(-\)0.14 & 0.06 & \(-\)0.24 & \(-\)0.57 & 0.17 \\ Vigorous & \(-\)0.93 & 0.93 & \(-\)0.93 & 1.00 & \(-\)0.43 & 0.31 & 0.09 & 0.06 & 0.37 & \(-\)0.28 \\ Ragpy & 0.24 & \(-\)0.20 & 0.58 & \(-\)0.43 & 1.00 & 0.61 & 0.74 & \(-\)0.83 & \(-\)0.82 & \(-\)0.51 \\ Coarse & \(-\)0.48 & 0.49 & \(-\)0.14 & 0.31 & 0.61 & 1.00 & 0.89 & \(-\)0.82 & \(-\)0.55 & \(-\)0.92 \\ Hoarse & \(-\)0.31 & 0.33 & 0.06 & 0.09 & 0.74 & 0.89 & 1.00 & \(-\)0.86 & \(-\)0.62 & \(-\)0.83 \\ Consonant & 0.13 & \(-\)0.17 & \(-\)0.24 & 0.06 & \(-\)0.83 & \(-\)0.82 & \(-\)0.86 & 1.00 & 0.79 & 0.75 \\ Mellow & \(-\)0.27 & 0.26 & \(-\)0.57 & 0.37 & \(-\)0.82 & \(-\)0.55 & \(-\)0.62 & 0.79 & 1.00 & 0.51 \\ Pure & 0.47 & \(-\)0.48 & 0.17 & \(-\)0.28 & \(-\)0.51 & \(-\)0.92 & \(-\)0.83 & 0.75 & 0.51 & 1.00 \\ \hline \hline \end{tabular}
\end{table}
Table 4: A correlation matrix for 10 timbre evaluation terms.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Name** & **Correlation Coefficient** \\ \hline \(\#\)\% (\#\)\% (Bright–Dark) & \(-\)0.99 \\ \(\#\)\% (Raspy–Mellow) & \(-\)0.82 \\ \(\#\)\% (Sharp–Vigorous) & \(-\)0.93 \\ \(\#\)\% (Coarse–Pure) & \(-\)0.92 \\ \(\#\)\% (Hoarse–Consonant) & \(-\)0.86 \\ \hline \hline \end{tabular}
\end{table}
Table 5: An ordinary timbre evaluation term system including five pairs of evaluation terms in their original language (Chinese) and the associated English translations.