Multi-frequency tone detector
View Patent ↗A tone detector for detecting a tone having a plurality of targeted frequencies comprises a first filter bank providing frequency estimates for an initial indication of a presence of each of the targeted frequencies; a second filter bank being controlled by the frequency estimates and comprising a plurality of filters operating in different frequency bands, each frequency band comprising at least one of the targeted frequencies, each of the filters providing a modified signal; a third filter bank extracting a noise signal from the input signal; a plurality of level control units (LCU) providing normalized modified signals having a constant amplitude; a power estimation module providing a power estimation parameter for each of the modified signals and the noise signal; and a discrimination module controlling a plurality of demodulator modules, each of the demodulator units providing a fine estimate of one of the targeted frequencies.
1. A tone detector for detecting a tone having a plurality of targeted frequencies, comprising:
a first filter bank receiving an input signal and providing frequency estimates for an initial indication of a presence of each of said targeted frequencies;
a second filter bank receiving said input signal and being controlled by said frequency estimates and comprising a plurality of filters operating in different frequency bands, each frequency band comprising at least one of said targeted frequencies, each of said filters providing a modified signal;
a third filter bank receiving said input signal and being controlled by said frequency estimates and extracting a noise signal from said input signal;
a plurality of level control units (LCU) receiving said modified signals and providing normalized modified signals having a constant amplitude;
a power estimation module providing a power estimation parameter for each of said modified signals and said noise signal; and
a discrimination module receiving said power estimation parameters and controlling a plurality of demodulator modules receiving said normalized modified signals, each of said plurality of demodulator units providing a fine estimate of one of said targeted frequencies.
2. The tone detector as claimed in claim 1 , comprising a decision logic module receiving said fine estimates of said targeted frequencies, comparing said fine estimates with predefined values and providing a tone detection result.
3. The tone detector as claimed in claim 2 , wherein said predefined values are standardized values defined according to a recommendation by the International Telecommunications Union (ITU).
4. The tone detector as claimed in claim 1 , wherein said first filter bank comprises Goertzel filters.
5. The tone detector as claimed in claim 1 , wherein said second filter bank comprises adaptive peak filters.
6. The tone detector as claimed in claim 1 , wherein said third filter bank comprises notch filters.
7. The tone detector as claimed in claim 1 , wherein said plurality of LCUs matches a duration of said normalized modified signals to a duration of said input signal.
8. The tone detector as claimed in claim 1 , wherein said discrimination module controls said demodulator modules based on an evaluation of at least one of a plurality of parameters derived from said power estimation parameters.
9. The tone detector as claimed in claim 8 , wherein said plurality of parameters comprises a twist of said targeted frequencies, a signal-to-noise ratio (SNR) of said modified signals and said noise signal, and a minimum level of said power estimation parameters.
10. The tone detector as claimed in claim 1 , wherein said demodulator modules provide said fine estimates of said targeted frequencies by determining energy operators for said fine estimates.
11. The tone detector as claimed in claim 1 , wherein said tone is a dual-tone multi-frequency (DTMF) signalling tone.
12. A method for detecting a tone having a plurality of targeted frequencies, comprising:
applying an input signal to a first filter bank; and
providing a frequency estimate for an initial indication of a presence of each of said targeted frequencies;
providing said input signal to a second filter bank being controlled by said frequency estimate and comprising a plurality of filters operating in different frequency bands, each frequency band comprising at least one of said targeted frequencies, each of said filters providing a modified signal;
providing said input signal to a third filter bank being controlled by said frequency estimate and extracting a noise signal from said input signal;
providing said modified signals to a plurality of level control units (LCU) providing normalized modified signals having a constant amplitude;
providing each of said modified signals and said noise signal to a power estimation module providing a power estimation parameter for each of said modified signals and said noise signal;
providing said power estimation parameters to a discrimination module controlling a plurality of demodulator modules receiving said normalized modified signals, each of said plurality of demodulator modules providing a fine estimate of one of said targeted frequencies.
13. A telecommunications apparatus, comprising a tone detector as claimed in claim 1 .
14. The telecommunications apparatus as claimed in claim 13 , wherein said apparatus is a media gateway, a telephone exchange, or a private branch exchange (PBX).
15. A computer program product, comprising code portions for executing steps of a method for detecting a tone having a plurality of targeted frequencies, when run on a programmable apparatus, the steps comprising:
applying an input signal to a first filter bank;
providing a frequency estimate for an initial indication of a presence of each of said targeted frequencies;
providing said input signal to a second filter bank being controlled by said frequency estimate and comprising a plurality of filters operating in different frequency bands, each frequency band comprising at least one of said targeted frequencies, each of said filters providing a modified signal;
providing said input signal to a third filter bank being controlled by said frequency estimate and extracting a noise signal from said input signal;
providing said modified signals to a plurality of level control units (LCU) providing normalized modified signals having a constant amplitude;
providing each of said modified signals and said noise signal to a power estimation module providing a power estimation parameter for each of said modified signals and said noise signal;
providing said power estimation parameters to a discrimination module controlling a plurality of demodulator modules receiving said normalized modified signals, each of said plurality of demodulator modules providing a fine estimate of one of said targeted frequencies.
16. The tone detector as claimed in claim 2 , wherein said first filter bank comprises Goertzel filters.
17. The tone detector as claimed in claim 3 , wherein said first filter bank comprises Goertzel filters.
18. The tone detector as claimed in claim 2 , wherein said second filter bank comprises adaptive peak filters.
19. The tone detector as claimed in claim 2 , wherein said third filter bank comprises notch filters.
20. The tone detector as claimed in claim 2 , wherein said plurality of LCUs matches a duration of said normalized modified signals to a duration of said input signal.