| 摘要 |
In a companding arrangement, the presence of a tone in only one of the two transmission directions is detected. Upon such detection, for example during set-up of a telephone call via a satellite transmission channel, the tone is compressed or expanded, depending on its transmission direction, separately from the remainder of the signal using a second compander. Companding is thus effected using two companders operating at different amplitude levels, with a consequent noise level reduction. A single bandpass filter is used to separate the detected tone, switches being controlled by the tone detection to couple the bandpass filter selectively for operation in either transmission direction.
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