Method and apparatus for performing high-density DTMF, MF-R1, MF-R2 detection

Abstract

Detectors determine the presence of valid sinusoids for DTMF, MF-R1 and MF-R2 protocols for encoding dialed digits. The detectors split electrical signals into subbands. Energies within the subbands are analyzed to determine a presence of sinusoids corresponding to frequencies of dialed digits. In one embodiment, the detectors comprise a PS-IIR filter to split the electrical signal into the subbands. The detectors further comprise at least one bank of filters, such as notch filters, corresponding to the number of possible relevant frequencies within the respective subbands. The detectors further comprise detection logic comprising tests, which may include analyzing the output(s) from the bank of filters. Optionally, a preclassifier is employed to predetermine which filters in the banks of filters are to be executed. The detectors, typically deployed in digital signal processors, allow for an increase in the density of detectors and provide robust performance in talk-off situations.

1 . A method of determining a presence of sinusoids in an electrical signal, comprising: 
 splitting the electrical signal into subbands having a common sampling frequency of less than twice the highest frequency of sinusoids in the electrical signal; and    analyzing energies within the subbands at the common sampling frequency to determine the presence of the sinusoids.    
   
   
       2 . The method according to  claim 1 , wherein the sinusoids correspond to frequencies of dialed digits.  
   
   
       3 . The method according to  claim 1 , wherein splitting the electrical signal into the subbands comprises extracting subbands of 0-1 kHz and 1-2 kHz.  
   
   
       4 . The method according to  claim 1 , wherein splitting the electrical signal into the subbands comprises filtering the electrical signal using a power symmetric infinite impulse response (PS-IIR) filter.  
   
   
       5 . The method according to  claim 4 , wherein the PS-IIR filters are implemented in a polyphase form.  
   
   
       6 . The method according to  claim 4 , wherein the PS-IIR filters comprise all-pass sections implemented in compact realizations.  
   
   
       7 . The method according to  claim 1 , further comprising filtering the subbands with at least one bank of filters comprising filters corresponding to the number of possible frequencies of the sinusoids within the respective subbands.  
   
   
       8 . The method according to  claim 7 , wherein the filters are notch filters.  
   
   
       9 . The method according to  claim 7 , wherein, for DTMF detection, splitting the electrical signal comprises (i) extracting a 0-1 kHz subband and a 1-2 kHz subband and (ii) filtering the subbands with four notch filters per bank of filters.  
   
   
       10 . The method according to  claim 7 , wherein, for MF-R1 detection, splitting the electrical signal comprises (i) extracting a 0-1 kHz subband and a 1-2 kHz subband and (ii) filtering the 0-1 kHz subband with two notch filters and the 1-2 kHz subband with four notch filters.  
   
   
       11 . The method according to  claim 7 , wherein: 
 for MF-R2 forward detection, splitting the electrical signal comprises (i) extracting a 0-1 kHz subband and 1-2 kHz subband and (ii) filtering the 1-2 kHz subband with six notch filters; and    for backward detection, splitting the electrical signal comprises (i) extracting a 0-1 kHz subband and a 1-2 kHz subband and (ii) filtering the 0-1 kHz subband with a notch filter at 980 Hz, to remove aliasing of a 1020 Hz tone in the 1-2 kHz subband, and four other notch filters and the 1-2 kHz subband with two notch filters.    
   
   
       12 . The method according to  claim 7 , further comprising preclassifying the sinusoids in the subbands and selecting filters within respective banks of filters that match frequencies of the preclassified sinusoids.  
   
   
       13 . The method according to  claim 1 , wherein analyzing energies comprises determining whether a summing of the energies in the subbands exceeds a minimum threshold level.  
   
   
       14 . The method according to  claim 1 , wherein analyzing energies comprises determining whether a difference between the energies in the subbands is below a twist-test threshold.  
   
   
       15 . The method according to  claim 1 , wherein for each subband, analyzing energies comprises comparing energy levels of an output of a notch filter having a lowest output energy level from among at least two notch filters in a bank of filters to the energy of the input signal to the bank of filters.  
   
   
       16 . The method according to  claim 1 , wherein analyzing energies further comprises reporting valid dialed digits.  
   
   
       17 . The method according to  claim 1 , wherein the electrical signal is sampled by an analog-to-digital converter and splitting the electrical signal and analyzing energies is executed by a digital processor.  
   
   
       18 . An apparatus, comprising: 
 a splitter to separate an electrical signal into subbands having a common sampling frequency of less than twice the highest frequency of sinusoids in the electrical signal; and    an analyzer to measure energies within the subbands at the common sampling frequency to determine a presence of the sinusoids.    
   
   
       19 . The apparatus according to  claim 18 , wherein the sinusoids correspond to frequencies of dialed digits.  
   
   
       20 . The apparatus according to  claim 18 , wherein the splitter extracts subbands of 0-1 kHz and 1-2 kHz.  
   
   
       21 . The apparatus according to  claim 18 , wherein the splitter comprises a power symmetric infinite impulse response (PS-IIR) filter to separate the electrical signal into the subbands.  
   
   
       22 . The apparatus according to  claim 18 , further comprising at least one bank of filters to filter the subbands, the bank of filters comprising filters corresponding to the number of possible frequencies of sinusoids within the respective subbands.  
   
   
       23 . The apparatus according to  claim 22 , wherein the filters are notch filters.  
   
   
       24 . The apparatus according to  claim 22 , further comprising at least one preclassifier to determine the sinusoids in the subbands and to select filters within respective banks of filters that match frequencies of the sinusoids.  
   
   
       25 . The apparatus according to  claim 18 , wherein the electrical signal is sampled by an analog-to-digital converter and the splitter and analyzer are implemented in digital processor instructions and executed by a digital processor.  
   
   
       26 . The apparatus according to clam  18 , being employed in a device supporting voice-over-IP.  
   
   
       27 . An apparatus, comprising: 
 an analog-to-digital converter to sample a received analog signal and to output a corresponding digital signal; and    a digital processor coupled to an output of the analog-to-digital converter to receive the digital signal and to execute program instructions to: 
 split the digital signal into subbands having a common sampling frequency of less than twice the highest frequency of sinusoids in the digital signal; and  
 analyze energies within the subbands at the common sampling frequency to determine a presence of the sinusoids.  
   
   
   
       28 . A computer-readable medium having stored thereon sequences of instructions, the sequences of instructions including instructions, when executed by a processor, causes the processor to perform: 
 splitting an electrical signal into subbands having a common sampling frequency of less than twice the highest frequency of sinusoids in the electrical signal; and    analyzing energies within the subbands at the common sampling frequency to determine a presence of sinusoids.    
   
   
       29 . A voice-over-IP device, comprising: 
 a receiver to receive electrical signals composed of voice signals and dialed digit sinusoids corresponding to dialed digits; and    a detector coupled to the receiver to monitor the electrical signals and to detect the dialed digit sinusoids, said detector including: 
 a splitter to split the electrical signal into subbands having a common  
 sampling frequency of less than twice the highest frequency of the dialed digit sinusoids; and  
 an analyzer to analyze energies within the subbands at the common sampling frequency to determine a presence of the sinusoids; and  
 a generator to generate packets of data comprising (i) voice signal data and (ii) information corresponding to the dialed digits.