Recording and playback circuit with Dolby noise reduction function and detection method

Recording and playback circuit with Dolby noise reduction function and detection method

Shown is the recording and playback circuit and detection method with Dolby noise reduction function . This circuit can be used in higher-end radio cassette players. The Dolby
noise reduction circuit enhances the high-frequency small signals during recording so that the small signals will not be buried in the background noise during recording, and during playback, the
high-frequency small signals are attenuated by the same amount. After attenuation, the small signal is restored to its original state, and the noise is also attenuated by the same amount, achieving an overall noise reduction
effect. Due to the high circuit precision requirements, they are all manufactured in integrated circuits.
    When recording, the signal is input from the ① and @ pins. After being boosted by the small signal, it is output by the @ and @ pins and then sent to the recording head.
    In the playback state, the output of the playback head is sent to the ③ pin and @ pin of the integrated circuit (HA12134/5/6A), and is output from the @ pin and @ pin after noise reduction
processing . During detection, the audio sinusoidal signal is sent from the input end, and the amplitude, waveform and distortion method are detected at the output end as shown in the figure.