Abstract: A tape recorder comprises, in its signal recording path, a variable gain circuit compensating the sound recording sensitivity of a magnetic tape and two variable equalizers compensating the frequency characteristic of the magnetic tape in the intermediate and high frequency ranges respectively. Reference signals at three different frequencies are successively supplied to the signal recording path to be recorded on the magnetic tape, and the signals of different reference frequencies are successively reproduced from the magnetic tape to be then arithmetically processed so as to optimize the gain of the variable gain circuit and the degree of frequency characteristic compensation by the first and second variable equalizers.

Abstract: A gain control circuit comprising a pair of transistors constituting a differential amplifier, and a pair of resistors each connected to the emitter of one of the transistors and having a sufficiently great resistance value compared with 1/gm of the transistor in the transistor operating range, the resistors being connected to a common regulated current supply to supply the halves of control current from the regulated current supply to the respective transistors, a pair of diodes are connected to the collectors of the respective transistors as a load, and a first variable resistor means is disposed in the current path traced from the diodes to the regulated current supply via the transistors and resistors for compensating fluctuation of the diffused resistance of the diodes. Further, a second variable resistor means is disposed in the base bias circuit for the transistors for compensating fluctuation of the base-emitter voltage of the transistors.

Abstract: Disclosed is a gain control circuit which comprises a gain control section including as its essential component a differential amplifier with which diodes or transistors arranged to act as diodes are connected as a load, and a control signal section including a logarithmic compression circuit and an exponential expansion circuit and providing a control signal for control of the gain of the gain control section. A temperature compensation circuit having a temperature dependence cancelling both the temperature dependence of the gain control section and that of the control signal section is provided in the bias circuit for the transistor in the last stage of the control signal section, so that the desired temperature compensation for the entire gain control circuit can be achieved at a single point.

Abstract: A PCM recording and reproducing apparatus comprising an error detecting circuit for detecting a frame including at least one word information signal with an error, the frame being a reproduction signal read from a recording medium on which certain pulse coded information is recorded in a frame distribution system, and a compensating circuit for compensating the reproduced information signal by the use of the output signal from the error detecting circuit, thereby removing the adverse effects of information dropout in spite of a high density recording.