Abstract: A contents database in which data of contents enciphered by a C key is stored and provided for a contents server, wherein the contents data enciphered by the C key are enciphered by an M key and sent to a user machine. In the user machine, the contents data enciphered by the C key are stored in a storage device. Upon reproduction, the contents data enciphered by the C key from the storage device are sent to an enciphering/decoding processing unit and decoded and charging is performed in accordance with the C key. A dynamic authenticating code which dynamically changes with the elapse of time is added to the C key.

Abstract: A microphone apparatus having a microphone for producing a desired audio signal, includes an adaptive signal processing section which is supplied with a reference signal based on a vibration detected signal from a vibration detecting circuit in response to a vibration of a vibration generating source whose vibration is picked up by the microphone and becomes an unnecessary noise signal, or in response to a control signal for controlling a drive source of a driving unit of a recording apparatus for recording an output signal from the microphone and which reduces a noise signal contained in the audio signal.

Abstract: In an active equalizer for selectively boosting or attenuating predetermined frequencies of audio or other electrical signals, and which comprises an inverting amplifier having an inverting input which receives the input signal through an input resistance and an output connected with the inverting input through a feedback resistance and at which the equalized output is derived, and an active filter for determining the frequencies to be boosted or attenuated; there is further provided a change-over switch having a boosting position in which the input signal is applied to the active filter, an attenuating position in which the output of the inverting filter is applied to the active filter and a neutral position, and a potentiometer connected between the output of the active filter and the inverting input of the inverting amplifier and being operable in concert with the change-over switch for determining the extent to which the frequencies determined by the active filter are boosted or attenuated.