Boots – shoes – and leggings
Patent
1989-05-03
1992-06-02
Nguyen, Long T.
Boots, shoes, and leggings
364726, G06F 1531, G06F 734
Patent
active
051193221
ABSTRACT:
A digital dual tone multi-frequency (DTMF) tone receiver having a detector circuit for scanning incoming audio signals for possible presence of DTMF tones, and a verifier circuit for verifying the presence of the detected DTMF tones. The detector circuit performs successive discrete Fourier transforms on the incoming signal at a first level of accuracy, and in response generates a tone verify flag signal for indicating whether or not a DTMF tone has been detected. The verifier circuit is enabled in the event that the tone verify flag signal indicates detection of a DTMF tone. The verifier circuit then performs further discrete Fourier transforms on the incoming signal at the detected DTMF frequencies as well as frequencies adjacent thereto, at a second level of accuracy greater than that provided by the detection circuit. The verifier circuit generates a tone present flag signal for indicating whether or not the detected DTMF tone is actually present. The detector and verifier circuits are preferably implemented algorithmically within a digital signal processor.
REFERENCES:
patent: 4223185 (1980-09-01), Picou
patent: 4328398 (1982-05-01), Kawaguchi et al.
patent: 4484035 (1984-11-01), Graham et al.
patent: 4709344 (1987-11-01), Crawford
Mitel Corporation
Nguyen Long T.
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