Yamaha Corporation

Masamitsu Hirano

Masao Noro

Nobuaki H Tsuji

Yasuhiko Sekimoto

Kunihiko Mitsuoka

Noro Masao

An input signal (SIN) is inverted by an inverter (), and the inverted input signal is entered into a tri-state type inverter (). An output portion of this inverter is connected via a delay path () to an input portion of an operational amplifier (). This operational amplifier owns a hysteresis characteristic with respect to a signal entered thereinto. An exclusive-OR gate circuit () controls to set the output state of the inverter to a low impedance state upon receipt of a signal (S) obtained by inverting the input signal, and controls to set the output state of the inverter to a high impedance state upon receipt of a signal (S) output from the operational amplifier. As a result, an amplitude of a signal (S) is limited to a constant amplitude in response to the hysteresis characteristic of the operational amplifier (), and a delay time is made constant.

Delay circuit

A sound field expanding apparatus is formed from an L-channel sound field expanding circuit and an R-channel sound field expanding circuit that have substantially the same circuit structure. Left and right stereophonic input signals of two channels are input in the L-channel sound field expanding circuit and the R-channel sound field expanding circuit, respectively. The L-channel sound field expanding circuit and the R-channel sound field expanding circuit include a first amplitude/phase characteristic changing circuit and a second amplitude/phase characteristic changing circuit, respectively. The first amplitude/phase characteristic changing circuit and the second amplitude/phase characteristic changing circuit add specified amplitude/phase characteristics to the respective input signals to generate a specified sound field expanding effect. The first and second amplitude/phase characteristic changing circuits are formed on a single IC chip with switched capacitor filters, and have the same structure for both of the first and second amplitude/phase characteristic changing circuits.

Sound field processor with sound field expanding apparatus

There are provided a waveform shaper that shapes a waveform of a one-bit data signal obtained by subjecting an input data signal to sigma-delta modulation, to generate an output data signal, and a sigma-delta D/A converter incorporating the waveform shaper. A clock jitter-detecting device detects jitter of a clock signal used for generating the one-bit data signal and generates an error signal indicative of the detected jitter of the clock signal. An amplitude-adjusting device shapes the waveform of the one-bit data signal by using the clock signal, and adjusts amplitude of the shaped one-bit data signal in response to the error signal, to generate the output data signal.

Waveform shaper and sigma-delta D/A converter

A digital-to-analog converting section includes a delta-sigma (.DELTA..SIGMA.) modulator and converts an input digital signal to an analog signal on the basis of delta-sigma modulation of the input digital signal by the delta-sigma modulator. A digital adder is provided, at the input stage of the digital-to-analog converting section, to add an oscillation-preventing direct current value to the input digital signal, and the adder operates to prevent oscillation in the delta-sigma modulating loop when the input digital signal changes from an 'input signal present' state to a 'no input signal' state. Also, an output buffer is provided, at the output stage of the digital-to-analog converting section, to shift the converted analog signal in response to an offset-adjusting current. Thus, the offset adjustment can be effected without adversely influencing the oscillation-preventing action of D.C. dithers.

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Hamamatsu, Japan

Masamitsu Hirano