| 摘要 |
<p>PURPOSE:To accurately decide a line state even if white noise in a large level appears in a test signal by providing a filter which causes only the test signal to pass through, and a filter which causes signals except for the test signal to pass through, and obtaining the power ratio of the output signals in both filters. CONSTITUTION:A sine wave signal is generated in the originator 2 of a sound encoding device (transmission equipment) 1 and is supplied to a line 3. A decoder (reception equipment) 4 has the band pass filter 5 which causes only the signal of a frequency component which is substantially similar to the sine wave signal to pass through, and the band prevention filter 9 which prevents the signal with the frequency component that is substantially similar to the sine signal from passing and which causes the signals with the frequency components except for said signal to pass. Detectors 6 and 10 take the absolute values of the output signals from the filters 5 and 9, the signals are full wave-rectified, and are changed into direct current components in low pass filters 7 and 11, are converted into electric power in power computing elements 12 and 13, whereby a rate is obtained in a rate computing element 16. A deciding unit 17 decides the state of the line 3 to defective if the rate is smaller than a prescribed value, and decides it to be good except for the case.</p> |
