The invention is directed to change a gain of the received light intensity at a stable rate, with respect to sensitivity adjustment manipulations. A photoelectric sensor amplifies a received light intensity signal generated through light projection processing and light receiving processing, and performs detection processing using the amplified received light intensity signal. The photoelectric sensor is provided with a device (a variable resistor) generating an adjustment command signal changing linearly with respect to sensitivity adjustment manipulations performed by a user. Further, the sensor is provided with an amplification processing part including a variable gain amplifier which is adapted such that the aforementioned adjustment command signal is inputted thereto. Further, the variable gain amplifier is adapted to convert the signal into a gain control signal changing exponentially with respect to sensitivity adjustment manipulations and, further, is adapted to perform amplification processing using a gain according to the gain control signal.

An amplifier includes an amplifying element that amplifies an input signal; an output terminal that outputs the signal amplified by the amplifying element; a matching circuit disposed in series between the amplifying element and the output terminal, and performing impedance matching; an impedance converter disposed in series between the amplifying element and the matching circuit or between the matching circuit and the output terminal; and a first resonator and a second resonator connected at the ends of the impedance converter.

The present invention relates to a signal processing apparatus and method, a program, and a data recording medium configured such that the playback level of an audio signal can be easily and effectively enhanced without requiring prior analysis.

An analyzer 21 generates mapping control information in the form of the root mean square of samples in a given segment of a supplied audio signal. A mapping processor 22 takes a nonlinear function determined by the mapping control information taken as a mapping function, and conducts amplitude conversion on a supplied audio signal using the mapping function. In this way, by conducting amplitude conversion of an audio signal using a nonlinear function that changes according to the characteristics in respective segments of an audio signal, the playback level of an audio signal can be easily and effectively enhanced without requiring prior analysis. The present invention may be applied to portable playback apparatus.

An audio signal processing device includes an audio signal control line including controllers for controlling a present value of each of a frequency characteristic, loudness, sound volume, fader of an input audio signal to designated values to be outputted, a zero crossing detector for detecting a timing when an amplitude of the input audio signal crosses a zero level of the audio signal; and a switching controller for switching the present value into the designated value in response to a switching command signal at the timing detected by the zero crossing detector. In this configuration, the zero level crossing timing of the audio signal is detected, and a designated controller makes the control operation at the zero level crossing timing. The click from a speaker can be eliminated.

An object is to provide a sound producer volume control apparatus capable of switching sound volume in a multiple stage and arranged by employing a smaller number of components. A sound producer volume control apparatus is comprised of: a sound producer (13); two resistors (Ra), (Rb) series-connected to a drive circuit of the sound producer (13); two switch units (SW1), (SW2) parallel-connected to the resistors (Ra), (Rb) respectively; a control unit (11) for ON/OFF-controlling the switch units (SW1), (SW2) in response to control signals (C1), (C2); an NPN transistor (Qf) series-connected to the sound producer (13); and a sound producing pattern generator (15) for ON/OFF-controlling the NPN type transistor (Qf) in response to a sound producing pattern signal (f). In this sound producer control units (SW1), (SW2) are ON/OFF-controlled by the control signals (C1), (C2) so as to variably select the resistance values connected to the sound producer (13), so that sound volume of the sound producer (13) is controlled in a stepwise manner.