| 摘要 |
Acoustic dialers are widely used to dial telephone numbers by generating a pair of DTMF tones for each key being depressed. Non-linearities in telephone systems, acoustic dialer loudspeakers, and telephone microphones may cause interfering tones to be produced due to mixing of generated DTMF tones. These interfering tones are especially problematic when they are near the frequencies of the DTMF tones and have similar amplitudes. When these interfering tones are received by a receiver decoder, the decoder may be unable to distinguish the interfering tones from the DTMF tones, and consequently the decoder may reject the DTMF tones received. The present invention prevents these types of rejections by generating a supplemental tone in addition to the normal DTMF tones. This supplemental tone attenuates the interfering tones so that receiver decoders can distinguish the interfering tones from the DTMF tones.
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