Abstract: A sound system with a howling-prevention function comprises an all-pass filter having group delay characteristics, which vary with the elapse of time, provided on a line used for the transmission of an audio signal from a microphone. Owing to the provision of such a sound system, any deterioration in the sound quality with respect to high frequencies and a chorus phenomenon is not produced, thereby making it possible to prevent howling without causing inferior sound quality.

Abstract: There is disclosed a data processing apparatus in which when a data existence position pulse indicative of the input of a data signal is supplied, a process of the supplied data signal is started in response to the leading edge of the data existence position pulse, a pulse signal of a predetermined width is generated after the elapse of only a first predetermined time from the leading edge of the data existence position pulse, the generation of an output data signal indicative of the result of the process is blocked by a switch for the generating period of the pulse signal, and the output data signal indicative of the result of the process is relayed and transmitted by the switch for only a second predetermined time from the extinguishment of the pulse signal. Thus, only the effective data can be generated.

Abstract: A muting control circuit is provided in which muting is performed when any one of a plurality of unlock detection signals is detected, indicating circuits is unlocked or when a data error is detected in a demodulator. In this way, reading time can be shortened to the minimum time required for muting. In addition, when one unlock detection circuit is triggered due to a disorder in the input, the unlock detection signal is provided immediately, so that the muting control signal is supplied and muting can be performed even when there is a time delay before the unlock detection circuit detects an unlocked state.

Abstract: A demodulation clock generator circuit employed in a modulation system such as a bi-phase mark system is improved by including a frequency detector to speed up the initial processing of a data signal to be demodulated. The frequency detector generates a frequency detection signal which corresponds to a signal from an oscillator and a signal from a synchronization signal portion of the signal to be demodulated. The frequency detector includes a memory portion clocked by the oscillator for storing the states of the signal to be demodulated and a signal generating portion for supplying the frequency detection signal when information stored in the memory portion is the same as a synchronizing portion of the signal to be demodulated and has a frequency of less than a predetermined value.