In this study the rising speed (dL/dt ; dB/s) is employed to express the initial stage of auditory stimuli. It is a changing rate of sound pressure level at the onsent. In experiment I, Trapezoidal white noises with a fixed peak duration are presented at various rising speeds and at various peak levels. The results show that the N_1-P_2 amplitude increases with an increase of rising speed and is invariable in the change of peak level. Each peak latency decreases with an increase of rising speed and is invariable in the change of peak level. In experiment II, constant rising speeds (100, 200, 500 dB/s), an accelerated rising speed (100-200-500 dB/s), and a decelerated rising speed (500-200-100 dB/s) are used. In the case of 500-200-100 dB/s, the response is similar to that of 500 dB/s, but in the case of 100-200-500 dB/s, the response is different from that of 100dB/s and waves complicatedly. From the result of experiment I, the threshold of the response on rising speed is estimated to be about 75dB/s.
The piano consists of the following mechanisms : (a) transmission of energy from the hammer to the strings, (b) propagation of energy of the strings, (c) transmission of energy from the strings to the soundboard at the bridge, and (d) acoustic radiation by the vibration of the soundboard. These mechanisms are expressed in terms of an equivalent electric circuit model, which is simulated by computer programs. A nearly half-sinusoidal pulse which is produced by the hammer's stroke, propagates on the special transmission line, and is reflected by the impedance of the bridge and the fixed end. The transmission and reflection lead to the transformation and decay of the waveform. The driving velocity of the soundboard is made by supplying the summing forces of the strings at the bridge to the driving point impedance. This velocity produces the sound pressure whose waveform is determined by transmission characteristics of the soundboard. Artificial piano sound is produced from calculated waveforms by a D-A converter. When each fundamental frequency of the group of strings is slightly detuned, beats are produced in each partial which is inharmonic. The changes are slow in the lower partials, but the higher they become, the rapider their changes are. The decay rate of the sound is fast at the prompt sound, but it becomes slowly at the after sound. These are some causes that gives a delicate timbre to the piano.