| 摘要 |
PURPOSE:To reduce the deterioration in the S/N of an output analog signal by applying digital-analog conversion to a signal of a prescribed frequency after it is superimposed on an input digital audio signal so as to prevent generation of noise. CONSTITUTION:A digital audio signal obtained by applying pulse code modulation (PCM) to a carrier by, e.g., a sound signal comes to an input terminal 1. After the digital audio signal is latched by a data latch 2, the result is fed to an adder 3. On the other hand, a signal generator 4 generates a digital signal obtained applying digital modulation to the carrier by a single frequency signal having a frequency lower than the audible frequencies 20Hz-20kHz, e.g., an ultralow frequency signal such as 5Hz-1Hz, and gives the digital signal to an adder 3. The adder 3 adds digitally the 1st and 2nd digital signals extracted respectively from the data latch 2 and the signal generator 4 to produce the 3rd digital signal, which is fed to a D/A converter 5.
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