Back to results
US 5,353,345 AGranted
Method and apparatus for DTMF detection
AssigneeInternational Business Machines Corporation
InventorClaude Galand
Life of this patent
Estimating the term…
Abstract
A DTMF tone is detected through the tracking of two tunable filters HAVING coefficients within so-called tunnels each limited by thresholds derived from the tone frequency components to be detected. In and out-band energies E1(n) and E2(n) are used to further validate tone detection.
Claims8
A method for detecting a Dual Tone Multi Frequency (DTMF) signal in a received sampled input signal x(n) derived from a band-limited signal s(n), said tone including two predefined single frequency components being taken respectively within one out of two groups of predefined frequencies, said method including:
- setting a so-called tunnel for each one of said group frequencies, each tunnel being limited by an upper and a lower threshold derived from said one of said group frequencies;
- feeding the input signal x(n) into a first filtering means splitting x(n) frequency bandwidth into two bands each including one of said predefined groups of frequencies and deriving therefrom signals x1(n) and x2(n) respectively;
- feeding each said x1(n) and x2(n) into an adaptive digital filter each including one varying coefficient k1(n) and k2(n) respectively;
- tuning each of said adaptive filters and tracking said filter coefficients k1(n) and k2(n), said tracking including comparing each of said filter coefficients k1(n) and k2(n) with said upper and lower thresholds corresponding to one of said set tunnels to determine if said filter coefficients k1(n) and k2(n) each remain within one of said set tunnels for a minimum predefined time length;
- whereby a tone is being detected and identified.
2 more elements
Dependencies are inferred from the claim text.