This paper describes that 'Nagauta' samisen tones are analyzed and the several physical values are extracted using digital signal processing techniques, and that the synthesized tones based on these data are produced and studied with regard to the features of physical parameters contributing to the tone quality of samisen. Physical parameters of samisen tones are classified in the following, (1)attack noise, (2)spectrum, (3)overall amplitude envelope, (4)amplitude envelopes of each harmonic, and (5)time variance of pitch after attack transient, and they are analyzed on the several notes and the several playing styles. The results show that in the spectrum, amplitude levels of lower harmonics are very small, and in the amplitude envelope, they have very rapid raises and rather rapid exponential decays compared with other musical instrument tones. Using these data, the synthesized tones are made by means of additive synthesis and compared to the original tones of samisen. As a result, it is verified that the synthesized tones with the amplitude of each harmonic being time-variant have a rather good similarity to original samisen tones, and that the synthesized tones with attack noise in the attack transient part are distinguishably improved.
The conventional distortion methods such as copper cap, laminated core can not satisfy the recently developed low distortion reproduction system like PCM. Corresponding to this situation, we tried to analyse the force distortion of loudspeaker and develop the new low distortion techniques. The driving force of loudspeaker is expressed as Bli, whereby Bl is called the force factor and i is voice coil current. To reduce the driving force distortion, the force factor must be constant and the voice coil current has to be linear. From our analysis, the condition for the constant force factor is that the magnetic flux variation across the voice coil must be zero. For this purpose, two techniques are proposed by the authers;one is the magetic flux feedback(MFFB) and another is the pushpull construction. MFFB is the feedback system which cancels the flux varition across the voice coil. 2nd HD is reduced to 0. 03% at 90dB/m. The pushpull construction has a symmetrical magnetic circuit with a voice coil pair, so 2nd HD is reduced. To reduce the voice coil current distotion, the constant current drive amplifier is used. By this amplifier, 3rd HD is reduced to 0. 01% at 1W.
A quantization noise is inevitable in digitizing analog signals. If the input signal passes quickly through many quantization steps, the quantization noise has little correlation to input signals. But if the input signal level is very low and the quantization steps are few or a signal varies very slowly, the quantization noise has a sort of distortion with strong correlation to the input signal. By adding a random"dither"with a uniform probability density function equal to the quantization step Δ to a signal to be quantized and by subtracting the identical dither from the quantizer output, it is possible to make the quantization noise without correlation to the input signal and with a uniform distribution and the power Δ^2/12. however, hardware equipments such as AD or DA converter have the conversion erros different from the ideal quantizing characteristics. Usually these errors do not possess a uniform distribution. In quantizing a signal with these converters, adding and subtracting a dither of much larger amplitude will lead to average the errors and increase the accuracy. This paper includes the optimization of a dither for quantization of wide range audio signals and a brief explanation of the theory and the experiment to increase the accuracy of AD or DA converter by using a large amplitude dither.