Towards a Robust Speech Intelligibility Test in Japanese

For synthesizing voice quality expressed by adjectives, acoustical correlates to adjective ratings of speaker characteristics are investigated. First, two sentences uttered by each of 20 male and 19 female speakers are rated by 22 listeners on eight semantic-differential scales used in everyday life. This paper focuses on two scales relating to dynamic aspect of articulation: “resting – busy” and “articulate – inarticulate”. For each gender, several acoustic parameters of the top and bottom three speakers on each scale are compared. The results show that the “busy” voices have significant correlation to the normalized standard deviation of logarithmic F0 per mora duration. On the other hand, “articulate” voices have wider dispersion on the F1-F2 plane than “inarticulate” voices. In phoneme level, it is observed that the formant loci of “inarticulate” voices tend to have slower movement than “articulate” ones. INTRODUCTION In order to synthesize speech with desired speaker characteristics or to convert the voice quality of speech signal to any specific one expressed by adjectives, it is required to control the acoustical parameters correlated with the values on the adjective scales. There are several studies on acoustical correlates to the static aspect of speaker characteristics [1,2]. We have also investigated the intercorrelation between the ratings of the voice characteristic on 8 Japanese semanticdifferential (SD) scales and their acoustic parameters [3]. However, the acoustical correlates to the dynamic aspect of speaker characteristics have not been well investigated due to its varieties. This paper examines the relationship between SD scales of two adjectives (“resting busy” and “articulate inarticulate”) and dynamics of acoustical parameters: F0 dispersion for “resting” and formant loci for “inarticulate”. SUBJECTIVE EVALUATION The voice samples used are two sentences (28 and 33 mora) uttered by each of 20 male and 19 female speakers with standard dialect who were selected from 50 speakers for each gender. These were then evaluated on eight adjective ratings [4] (“clear hazy”, “resting busy,” “powerful weak”, “young old”, “deep shallow”, “sharp dull”, “articulate inarticulate” and ”nasal less nasal”) by 22 listeners for male voices and 8 for female voices. Each listener rates the voice attribute of each voice sample on each pair of adjectives. The six-point rating scale is ranged from 3 to -3 in which the value 1 to 3 correspond to the degree “a little” to “very”. The rates for each speaker were averaged over two sentences, listeners, and three trials. Fig.1 shows the speaker distribution of the average rates on the two SD scales of dynamic aspect of articulation: “resting busy” and “articulate inarticulate”. The ranges of the male and female speaker distributions on each scale are mostly same. Furthermore, the correlation between the rates of “resting” and “articulate” is significantly high (0.67 for male and 0.58 for female). ACOUSTICAL CORRELATES OF DYNAMIC SPEAKER CHARACTERISTICS Analysis method In this study, twelve acoustical parameters are extracted: the means and standard deviations of the logarithmic fundamental frequency (F0, sd_F0), the first to third logarithmic formant frequencies (F1, F2, F3, sd_F1, sd_F2, sd_F3), and their bandwidths, and speech rate in mora per second computed excluding pauses. Speech signal was digitized at a sampling frequency of 16kHz and analysis was performed with a frame length of 20ms and a frame shift of 10ms. Formant frequencies for each frame were extracted by means of a 12th order Mel-LPC analysis followed by a root solving, and pitch frequency are estimated by the cepstrum method. Results of the “busy” scale While the correlation between the SD values and each of twelve parameters was not significant for both genders, the following parameter was found to be highly correlated with the “busy” ratings.