| 摘要 |
To test the performance of a PCM terminal operating in the TDM mode, a simulated message or noise signal is generated by extracting a recurrent sequence of code words from a read-only memory, the stored code words representing a set of values logarithmically related to sucdessive amplitudes of a sine wave or other periodic oscillation to be reproduced. These words are read out at a fixed scanning frequency fo but with skipping of (p-l) memory stages if a signal frequency pfo is to be simulated. A volume selector generates supplemental code words which are additively or subtractively combined with the extracted code words to simulate a desired voltage level. The resulting code words are compressed in a code converter in which the quantum steps of the segments of a compander characteristic, conforming to the chosen logarithmic function, are stored in another read-only memory.
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