| 摘要 |
A codec is disclosed for encoding analog signals into compressed PCM (CPCM) and conversely for decoding CPCM information into analog signals. The signal to be encoded is compared with the decaying voltage on a capacitor, initially charged to a fixed voltage E, and being discharged through a fixed resistor to another fixed voltage - dE, the time being measured by a binary digital counter from the start of the discharge until the voltage at the capacitor terminal equals the absolute value of the analog signal to be encoded. With proper choice of constants and clock frequency, the content of the binary counter at the time of coincidence represents the desired pulse code in complementary binary form of the analog signal sample to be encoded. Only the sign bit has to be added, which can be easily obtained from the polarity of the signal sample. Conversely, at the receiving end, the CPCM signal may be decoded into analog signal samples by timing the discharge of a similar or identical RC-circuit in accordance with the received code.
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