| 摘要 |
PURPOSE:To remove a sound noise by eliminating the DC level difference of each head demodulated signal when recording sound signals having frequency modulation carriers changed, track by track, alternately by a two-head helical scan. CONSTITUTION:Both head outputs are passed through preamplifiers 1 and 2, band-pass filters 3 and 4, and demodulating circuits 5 and 6 respectively to obtain the 1st sound signal with a DC level E, and an AC level f1 and the 2nd sound signal with an E2 and f2. The 1st sound signal is inputted to the minus terminal of the 1st arithmetic circuit Q1which grounded at the plus terminal, and the 2nd sound signal is inputted to the plus terminal of the 2nd arithmetic circuit Q2 which is grounded at the minus terminal. The outputs of the 1st and the 2nd arithmetic circuits are supplied to the 3rd and the 4th arithmetic circuits Q3 and Q4 and also inputted to the 1st switch S1 changed over by an RF switching output to average the levels, but they contain AC errors. Those AC errors are passed through a DC cutting capacitor C and inputted to the plus and minus terminals of the 5th arithmetic circuit Q5 alternately through the 2nd analog switch S3. |
