The simplest structure of the universal function for generating synthetic speeches is a matter of considerable interest in this study. Even an inverse approach to extract speech information just like the auditory organ, but not the conventional filter model to reproduce multiple resonances based on the articulatory organ, has yielded more than 90 % of intelligibility and also 59 kbits/s of extraction rate, yet remaining the quality of syntheses mediocre. These results are interpreted as emphasized evidence that envelope maxima as well as maximal points in a bandpass filtered waveform play an essential role in the preservation of intelligibility and the timbre of synthetic speech, respectively. While the connection model of one-term cosine functions with linear approximation for both slowly-varying amplitude envelope and periodicity of inner fine structure contributes to lower spectral bands of speech synthesis, rapid and exceptional variation in higher spectral bands ( > 1kHz) causes degradation, which can be estimated by an index of phase error in advance.

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The embedded module of the popular Raspberry-pi system has facilitated the implementation of analyzer for tapping noise, transmitting a series of resultant index by wireless in realtime.Nowadays in Japan by the amendment of the law concerned, the hammering test with artificial intelligence has come into limelight again because the simple as well as economical time-based-maintenance should be carried out to prevent the lifted surfaces of numerous used-buildings over one decade from an even more serious falling-accident. The test belongs to resonance or reverberation recognition, which is caused by the degradation of an adhesive agent over time. Because both amplitude and frequency are varied in response to impact energy, we have proposed a robust index of the magnitude for resonance in the temporal domain, named half-life time ratio, H, which is further ascertained by phase error of the fourth physical quantity based on auditory cognitive processing in the brain. Only a dozen or so trials of tapping for a mere few seconds enable to display the histogram of resonance signals against spectral channel, accelerating the progress of automatic hammering test even without an established knowledge-base.

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