| 摘要 |
<p>A digital processing technique is employed in telecommunications arrangements to eliminate costly steep-slope filters previously necessary for the detection of multitone control signals in the presence of speech signals. The composite analogue signal (a) derived from the individual code tones is converted to a constant amplitude pulse train of which individual pulse lengths correspond to the interval between successive corssing points of the analogue signal. The digital signals so obtained (b) are compared with fixed predetermined digital signals corresponding to the n frequency combinations in the full code range. Since the pulse trains exhibit mirror symmetry of the beat interval, it is necessary only to carry out the comparison for half of this period.</p> |
