Abstract:
An apparatus having a first circuit and a second circuit is disclosed. The first circuit is configured to generate a first intermediate signal by expanding a first input signal subjected to a quantization. The second circuit is configured to generate a second intermediate signal based on a second input signal. The second intermediate signal approximates an echo in the first input signal caused by the second input signal. The second circuit is also configured to generate a third intermediate signal by companding the second intermediate signal to compensate the quantization of the first input signal.

Description:
[0001]    This application relates to U.S. Provisional Application 61/896,224, filed Oct. 28, 2013 and U.S. Provisional Application No. 61/868,229, filed Aug. 21, 2013, each of which are hereby incorporated by reference in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to echo cancellation in electrical telephone networks generally and, more particularly, to a method and/or apparatus for implementing an echo cancellation with quantization compensation. 
       BACKGROUND 
       [0003]    Conventional echo canceller performances are constrained to only about 38 decibels (i.e., dB) maximum echo return loss enhancement (i.e., ERLE). The constraint results from a quantization noise created by a compression and subsequent expansion through either μ-law codecs or A-law codecs used in telephone networks. An International Telecommunication Union Telecommunication Standardization Sector (i.e., ITU-T) Recommendation G.168 uses measurement techniques to assess the performance of specific implementations of an echo canceller. The limits used in the recommendation suggest no anticipation of better performance than the 38 dB of cancellation. 
       SUMMARY 
       [0004]    The invention concerns an apparatus having a first circuit and a second circuit. The first circuit is configured to generate a first intermediate signal by expanding a first input signal subjected to a quantization. The second circuit is configured to generate a second intermediate signal based on a second input signal. The second intermediate signal approximates an echo in the first input signal caused by the second input signal. The second circuit is also configured to generate a third intermediate signal by companding the second intermediate signal to compensate the quantization of the first input signal. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0005]    Embodiments of the invention will be apparent from the following detailed description and the appended claims and drawings in which: 
           [0006]      FIG. 1  is a block diagram of a system; 
           [0007]      FIG. 2  is a detailed block diagram of a canceller circuit in accordance with an embodiment of the invention; 
           [0008]      FIG. 3  is a detailed block diagram of a converter circuit; 
           [0009]      FIG. 4  is a detailed block diagram of a compander circuit and a filter circuit; 
           [0010]      FIG. 5  is a detailed block diagram of the compander circuit and another filter circuit; 
           [0011]      FIG. 6  is a detailed block diagram of a subtracter circuit; 
           [0012]      FIG. 7  is a partial block diagram of another canceller circuit; and 
           [0013]      FIG. 8  is a graph of a simulation of a best inverse echo return loss enhancement performance. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0014]    Embodiments of the invention include providing an echo cancellation with quantization compensation that may (i) improve a match between an estimated echo and an actual echo, (ii) improve overall cancellation compared with common techniques, (iii) avoid degradation to a normal performance of the echo canceller and/or (iv) be implemented in one or more integrated circuits. 
         [0015]    Some embodiments provide one or more techniques for improving performance of an echo canceller in the presence of either an A-law quantization or a μ-law quantization. The A-law quantization and the μ-law quantization are defined in an ITU-T Recommendation G.711. By using added functionality, a residual echo departing the echo canceller can be reduced below a normal maximum echo return loss enhancement of 38 decibels (e.g., dB). Experiments on simulations of the techniques have achieved echo return loss enhancements in the range of 45 dB to 50 dB. Under some circumstances, as much as 60 dB to 80 dB echo return loss enhancement has been achieved. Furthermore, the utilization of a nonlinear residual echo suppression at an output of the echo canceller can reduce or possibly eliminate the remaining echo under certain circumstances. 
         [0016]    Echoes result from 2-to-4 wire terminations found on most connections in public switched telephone networks. By adding a companding (e.g., quantizing and expanding) component to a structure of the echo canceller, a resulting quantization of an estimated echo improves a match between the estimated echo and the actual echo. The improved match allows for better overall echo cancellation, generally beyond the signal to quantization ratios that limit common echo canceller performance. 
         [0017]    Referring to  FIG. 1 , a block diagram of an example implementation of a system  90  is shown. The system (or architecture)  90  generally comprises a network (or transmission line)  92 , a block (or circuit)  94 , one or more blocks (or circuits)  96 , a block (or circuit)  98  and a block (or circuit)  100 . The circuits  92  to  100  may represent modules and/or blocks that may be implemented as hardware, software, a combination of hardware and software, or other implementations. 
         [0018]    An input signal (e.g., RIN) is shown received by the circuit  100 . The signal RIN carries input data (e.g., far-end speech) received from a far-end user. The circuit  100  generates and presents an output signal (e.g., SOUT). The signal SOUT carries output data (e.g., near-end speech) to the far-end user. An output signal (e.g., ROUT) is shown generated by the circuit  100  and transferred to the circuit  98  via the network  92 . The signal ROUT conveys processed versions of the data received in the signal RIN. The circuit  98  generates an input signal (e.g., SIN) that is transferred through the network  92  and received by the circuit  100 . The signal SIN carries input data (e.g., near-end speech) received from a near-end user. A bidirectional signal (e.g., TEL) is exchanged between the circuit  98  and the circuit  96 . The signal TEL carries far-end speech to the near-end user and near-end speech bound for the far-end user. The signal TEL is generally carried on a 2-wire cable. 
         [0019]    The network  92  may implement a telephone network. In some embodiments, the network  92  may be a plain old telephone system telephone line (e.g., Public Switched Telephone Network) in other embodiments, the network  92  may implement a private branch exchange (e.g., PBX). Other network designs may be implemented to meet the criteria of a particular application. 
         [0020]    The network  92  has a current condition among several possible conditions (or states or modes) at any given time. The possible conditions include, but are not limited to, a talk condition, a listen condition, a double talk condition, a silence condition and a tone condition. The talk condition is known as a far-end talk (or speech) condition. The listen condition is known as a near-end talk (or speech) condition. In some circumstances, two or more of the conditions may exist on the network  92  at the same time (e.g., the tone condition and the talk condition where a far user speaks during the tone condition). 
         [0021]    While in the talk condition (far-end speech), the far user is generally speaking and a near user is silent. Since the dominant data on the network  92  in the talk condition originates from the circuit  100 , the circuit  100  reduces an actual echo by applying synthesized echo cancellation data, updates (converges) the echo cancellation functionality, detects changes in the echo path of the network  92 , combined with the circuit  94 , and trains the echo cancellation functionality to match the echo path. 
         [0022]    While in the listen (near-end talk) condition, a near user is speaking and the far user is silent. While in the silent condition, both the far user and the near user are silent. If the far user is silent, the signal ROUT generally contains little or no data that could create an echo. Therefore, circuit  100  may stop the updates of the echo cancellation functionality and stop any training in progress. Under the silent condition, the signal SOUT is substantially similar to the signal SIN. 
         [0023]    While in the double talk condition, both the far user and the near user are speaking. Since the circuit  100  cannot distinguish far user data from near user data in the signal SIN under the double talk condition, the circuit  100  stops updating the echo cancellation functionality and stops any training in progress. Under the double talk condition, the signal SOUT is substantially similar to the near end talker signal after the estimation of the echo of the signal ROUT has been subtracted, with some possible residual of the un-cancelled echo. In some situations, the echo cancellation continues while in the double talk condition as the circuit  100  may reasonably estimate the echo components in the signal SIN caused by the outgoing data in the signal ROUT. While in the tone condition, the signal TEL generally conveys a continuous tone to the network  92  via the circuit  98 . While the tone is present on the network  92 , the circuit  100  stops the updating of the echo cancellation functionality and stops any training that may be in progress. 
         [0024]    The circuit  94  is shown implementing a central office circuit. The central office  94  communicates with one or more local circuits  96  via one or more signals TEL. The central office  94  is operational to convert between a  2 -write interface connection to the circuit  96  and a 4-wire interface connection to the network  92 . 
         [0025]    The circuit  96  is shown implementing a telephone. The circuit  96  communicates with the central office  94  via the signal TEL. The circuit  96  is considered the near end of the system  90 . 
         [0026]    The circuit  98  is shown implementing a converter circuit. The circuit  98  resides within the central office  94 . The circuit  98  is operational to convert between the 4-wire interface of the network  92  and the 2-wire interface to the circuit  96 . The circuit  98  is also operational to convert between a digital domain of the network  92  and an analog domain of the circuit  96 . 
         [0027]    The circuit  100  is shown implementing an echo canceller circuit. The circuit  100  is operational to transfer data between a far-end user and the network  92 , filter the data, perform network echo cancellation on the send data as received in the signal SIN, update the echo cancellation functionality to converge with the current echo characteristics of the circuit  98  and the network  92 , train the echo cancellation functionality to learn new echo characteristics and detect echo path changes in the circuit  98  and/or the network  92 . The echo cancellation includes generating an intermediate signal by expanding input data received in the signal SIN subjected to a quantization in the circuit  98 , generating another intermediate signal based on input data received in the signal RIN, where the other intermediate signal approximates an echo in the signal SIN caused by the signal RIN, and generating an additional intermediate signal by companding the other intermediate signal to compensate for the quantization of the signal SIN. In some embodiments, the circuit  100  is implemented as one or more integrated circuits (or chips or dies). 
         [0028]    Referring to  FIG. 2 , a detailed block diagram of an example implementation of the circuit  100  is shown in accordance with an embodiment of the invention. The circuit (or apparatus or device or integrated circuit)  100  generally comprises a block (or circuit)  102 , a block (or circuit)  104 , a block (or circuit)  106  and a block (or circuit)  108 . The circuit  104  generally comprises a block (or circuit)  110 , a block (or circuit)  112 , a block (or circuit)  114 , a block (or circuit)  115 , a block (or circuit)  116  and a block (or circuit)  118 . The circuits  102  to  118  may represent modules and/or blocks that may be implemented as hardware, software, a combination of hardware and software, or other implementations. 
         [0029]    The signal RIN is shown being received by the circuits  102 ,  110  and  118 . The signal ROUT is generated and presented by the circuit  102 . The circuit  106  is shown receiving the signal SIN. The signal SOUT is generated and presented by the circuit  108 . 
         [0030]    A signal (e.g., EXP 1 ) is shown being generated by the circuit  106  and transferred to the circuit  115 . The signal EXP 1  is an intermediate signal that carries expanded data as received in the signal SIN. A signal (e.g., Y 1 ) is shown being generated by the circuit  115  and received by the circuit  106 . The signal Y 1  is a filtered version of the signal EXP 1 . The circuit  116  generates a signal (e.g., E) received by the circuit  108 ,  112  and  118 . The signal E conveys error data caused by an echo during the far-end talk condition and near-end speech during a near-end talk condition, a double talk condition and/or a tone condition. 
         [0031]    A signal (e.g., X) is shown being generated by the circuit  110  and transferred to the circuit  112 . The signal X is an intermediate signal that carries a companded version of the data in the signal RIN. The circuit  112  generates a signal (e.g., Y 2 ) transferred to the circuits  114  and  115 . The signal Y 2  is an intermediate signal that carries a filtered version of the data from the signal X. A signal (e.g., EXP 2 ) is shown being generated by the circuit  114  and received by the circuit  115 . The signal EXP 2  is an intermediate signal that carries companded versions of the data in the signal Y 2 . The circuit  115  is shown generating a signal (e.g., Y 3 ) that is transferred to the circuit  116 . The signal Y 3  is either a filtered version of the signal EXP 2  or the signal Y 2 . The circuit  118  is shown generating a signal (e.g., C 1 ) received by the circuit  112 . The signal C 1  conveys control information that adjusts filtering operations in the circuit  112 . The circuit  118  also generates a signal (e.g., C 2 ) received by the circuit  115 . The signal C 2  is a control signal used to selectively bypass/not bypass the companding operations of the circuit  114 . 
         [0032]    During far talking, damage to the signal SIN caused by the system  90  is predictable because the damage is caused by a quantization through a known scheme. All other transfer characteristics between a digital-to-analog converter and an analog-to-digital converter in the central office  94  are linear transfer functions modeled by the adaptive filter of the circuit  112 . 
         [0033]    The circuit  102  is shown implementing a compresser/quantizer circuit. The circuit  102  is operational to compress the data received in the signal RIN to generate the signal ROUT. The compression function includes a quantization of the data per either the A-law technique or the μ-law technique. 
         [0034]    The circuit  104  is shown implementing an echo canceller (e.g., ECAN) circuit. The circuit  104  is operational to detect the characteristics of the circuit  98  and/or the network  92 , model an echo path of the circuit  98  and the network  92 , cancel echoes within the signal SIN created due to data in the signal ROUT, update the echo cancellation functionality and train the echo cancellation functionality. The echo cancelled data is presented in the signal E to the circuit  108 . 
         [0035]    The circuit  106  is shown implementing an expander circuit. The circuit  106  is operational to expand the data received in the signal SIN to generate the signal Y 1 . The expansion function generally reverses the compression/quantizing function performed by the circuit  98 . 
         [0036]    The circuit  108  is shown implementing a processor circuit. In some embodiments, the circuit  108  implements a nonlinear processor. The circuit  108  is operational to provide nonlinear residual echo cancellation of whatever echo remains in the signal E. 
         [0037]    The circuit  110  is shown implementing a compander circuit. The circuit  110  is operational to compress and subsequently expand the data in the signal RIN to generate the signal X. The compression function includes a quantization of the data per either the A-law technique or the μ-law technique. Including the circuit  110  in the circuit  100  can result in an improvement of approximately 3 db in the echo return loss enhancement compared with a system without the circuit  110 . In some situations, the signal RIN may already have experienced the correct quantization that matches the effects of circuit  102 . 
         [0038]    The circuit  112  is shown implementing an adaptive filter circuit. The circuit  112  is operational to filter the data received in the signal X to generate a synthesized echo in the signal Y 2  that approximately mimics the echo caused by the circuit  98  and the network  92 . The adaptive filtering is generally based on the tap values in the circuit  112  and a step size value, and other adaptation controls, received in the signal C 1  and the error values received in the signal E. 
         [0039]    The circuit  114  is shown implementing another compander circuit. The circuit  114  is operational to compress and subsequently expand the data in the signal Y 2  to generate the signal Y 3 . The companding in the circuit  114  matches the quantization seen on the signal SIN by applying the same quantization to the signal Y 2 . Therefore, the residual quantization error on the signal E can be reduced in the circuit  116  to a greater extent than in common techniques. The compression function includes a quantization of the data per either the A-law technique or the μ-law technique. The circuit  114  is also operational to bypass the companding operation as commanded by control information in the signal C 2 . The control signal C 2  might also be asserted during a double-talk, near-talk, silence or tone condition. 
         [0040]    The circuit  115  is shown implementing a filter circuit. The circuit  115  is operational to create the signal Y 1  by filtering the signal EXP 1 . The circuit  115  is also operational to create the signal Y 3  by filtering the signal EXP 2  or the signal Y 2 . Control of generation of the signal Y 3  is provided by the signal C 2 . 
         [0041]    The circuit  116  is shown implementing a subtracter circuit. The circuit  116  is operational to generate a difference between the synthesized echo received in the signal Y 3  and the actual echo as received in the signal Y 1 . The difference is an error value in the signal E. 
         [0042]    The circuit  118  is shown implementing a controller circuit. The circuit  118  is operational to control the overall operations of the circuit  104 . The circuit  118  controls the adaptive filter settings of the circuit  112  and the bypass/not bypass setting in the circuit  115  of the compander operation. In some embodiments, the bypass/not bypass of the companding operation in the circuit  114  is determined in response to a ratio of an average energy of the error signal E to an average energy of the signal Y 1 . In other embodiments, the bypass/not bypass determination for the companding is made in response to talk on both the signal SIN and the signal RIN. 
         [0043]    Referring to  FIG. 3 , a detailed block diagram of an example implementation of the circuit  98  is shown. The circuit  98  generally comprises a block (or circuit)  140 , a block (or circuit)  142 , a block (or circuit)  144 , a block (or circuit)  146 , a block (or circuit)  148 , a block (or circuit)  150  and a block (or circuit)  152 . The circuits  140  to  152  may represent modules and/or blocks that may be implemented as hardware, software, a combination of hardware and software, or other implementations. 
         [0044]    The signal ROUT is shown being received by the circuit  140 . The signal TEL is exchanged with the circuit  146 . The signal SIN is generated and transmitted by the circuit  152 . The echo is created across the circuit  146 . 
         [0045]    A signal-to-noise ratio at the central office  94  in the analog section is higher than the 38 dB created by the μ-law/A-law quantization. Therefore, the companding quantization from the circuits  140  and  152  constrains the overall signal-to-noise ratio and thus the echo cancellation performance. 
         [0046]    The circuit  140  is shown implementing an expander circuit. The circuit  140  is operational to expand the data received in the signal ROUT. The expansion function generally reverses the compression/quantizing function performed by the circuit  102 . 
         [0047]    The circuit  142  is shown implementing a digital-to-analog (e.g., D/A) converter circuit. The circuit  142  is operational to convert the expanded data created by the circuit  140  into an analog signal. The data entering the circuit  142  is in the digital domain. The data leaving the circuit  142  is in the analog domain. The analog data is presented to the circuit  144 . In some embodiments, the low pass filter function of the circuit  144  may be partly digital and partly analog, and so may span both sides of the circuit  142 . 
         [0048]    The circuit  144  is shown implementing a low pass filter (e.g., LPF) circuit. The circuit  144  is operational to low-pass filter the data received from the circuit  142 . The low-pass filtering provides an anti-aliasing feature to the circuit  98 . 
         [0049]    The circuit  146  is shown implementing a hybrid circuit. The circuit  146  is operational to route the receive data from the circuit  144  to the signal TEL and route the send data in the signal TEL to the circuit  148 . In some embodiments, the circuit  146  is implemented as a normal 4-wire to 2-wire hybrid circuit. The 2-wire interface generally connects to the telephone lines between the central office  94  and the one or more telephones  96 . Half of the 4-wire interface receives the data carried in the signal ROUT. The other half of the 4-wire interface presents data to the signal SIN. In some situations, the circuit  146  may leak some received data from the signal ROUT to the signal SIN thereby creating the echo. In common schemes, multiple circuits  146  may be distributed throughout the system  90 . In some embodiments, one or more additional circuits  146  may exist between the circuits  100  and  96 . Each of the multiple circuits  146  creates a corresponding echo. 
         [0050]    The circuit  148  is shown implementing a band pass filter (e.g., BPF) circuit. The circuit  148  is operational to band-pass filter the data received from the circuit  146 . The band-pass filtering provides an anti-aliasing feature to the circuit  98 . In some embodiments, the circuit  148  also removes power line frequencies (e.g., 60 Hertz) that may couple into the telephone lines. In some embodiments, the circuit  148  may be partly analog and partly digital and therefore, span across the circuit  150 . 
         [0051]    The circuit  150  is shown implementing an analog-to-digital (e.g., A/D) converter circuit. The circuit  150  is operational to digitize the analog data received from the circuit  148 . The digitized data is presented to the circuit  152 . 
         [0052]    The circuit  152  is shown implementing a compresser/quantizer circuit. The circuit  152  is operational to compress the data received from the circuit  150  to generate the signal SIN. The compression function includes a quantization of the data per either the A-law technique or the μ-law technique. 
         [0053]    Referring to  FIG. 4 , a detailed block diagram of an example implementation of the circuits  114  and  115  is shown. The circuit  114  generally comprises a block (or circuit)  160  and a block (or circuit)  162 . The circuit  115  generally comprises a block (or circuit)  164 , a block (or circuit)  166  and a block (or circuit)  168 . The circuits  160  to  168  may represent modules and/or blocks that may be implemented as hardware, software, a combination of hardware and software, or other implementations. 
         [0054]    The signal Y 2  is shown being received by the circuits  160  and  164 . A compressed signal (e.g., CQ) is generated by the circuit  160  and transferred to the circuit  162 . The signal CQ conveys a compressed and quantized version of the data in the signal Y 2 . A signal (e.g., EXP 2 ) is generated by the circuit  162  and presented to the circuit  164 . The signal EXP 2  conveys an expanded version of the compressed/quantized data in the signal CQ. A signal (e.g., YM) is shown being generated by the circuit  164  and received by the circuit  166 . The signal YM is an intermediate signal that selectively carries data from the signal Y 2  or the signal EXP 2 , depending on the control information in the signal C 2 . The signal Y 3  is shown being generated by the circuit  166 . The circuit  168  is shown receiving the signal EXP 1 . The signal Y 1  is shown being generated by the circuit  168 . 
         [0055]    The circuit  160  is shown implementing a compresser/quantizer circuit. The circuit  160  is operational to compress the data received in the signal Y 2  to generate the signal CQ. The compression function includes a quantization of the data per either the A-law technique or the μ-law technique. 
         [0056]    The circuit  162  is shown implementing an expander circuit. The circuit  162  is operational to expand the data received in the signal CQ to generate the signal EXP 2 . The expansion function generally reverses the compression/quantizing function performed by the circuit  160 . 
         [0057]    The circuit  164  is shown implementing a multiplexer circuit. The circuit  164  is operational to selectively multiplex either the signal Y 2  or the signal EXP 2  to the signal YM. The selection between the signal Y 2  and EXP 2  is controlled by the signal C 2 . 
         [0058]    The circuit  166  is shown implementing a high pass filter. The circuit  166  is operational to generate the signal Y 3  by high-pass filtering the signal YM. 
         [0059]    The circuit  168  is shown implementing a high pass filter. The circuit  168  is operational to generate the signal Y 1  by filtering the signal ExP 1 . The circuit  168  typically exists between the signal SIN and the signal Y 1  in the echo canceller (e.g., circuit  104 ). The circuit  166  provides similar changes in the signal Y 3  as the circuit  168  does in the signal Y 1 . 
         [0060]    The quantization process on the signal Y 2  is enabled during good performance after ordinary convergence has been achieved. A measurement of performance (e.g., PERF) is achieved by monitoring a ratio of the signal energy difference between the signal E and the signal Y 1 . The ratio is expressed by formula 1 as follows: 
         [0000]      PERF=(average  E   2 )/(average  Y 1 2 )  (1)
 
         [0000]    In some embodiments, if the performance value is less than a threshold, the signal Y 2  is quantized, expanded and routed through the circuit  164 . Otherwise, the companding operation is bypassed using the circuit  164  and the signal Y 3  matches the signal Y 2 . In other embodiments, a best value of the performance is tracked and used for gating the quantization. Using the gating technique allows for a fallback capability that enables the echo canceller circuit  104  to have at least a conventional performance. 
         [0061]    Referring to  FIG. 5 , a detailed block diagram of another example implementation of the circuit  114  and a circuit  115   a  is shown. The circuit  115   a  generally comprises the block  164 , the block  166 , a block (or circuit)  168  and the block  170 . The circuits  160  to  170  may represent modules and/or blocks that may be implemented as hardware, software, a combination of hardware and software, or other implementations. 
         [0062]    The signal Y 2  is shown being received by the circuits  160  and  160 . A signal (e.g., Y 4 ) is shown being transferred from the circuit  170  to the circuit  164 . The signal EXP 2  is shown being received by the circuit  166  from the circuit  162 . The circuit  166  generates a signal (e.g., Y 5 ) that is received by the circuit  164 . 
         [0063]    The circuit  164  is shown implementing the multiplexer circuit. The circuit  164  is operational to selectively multiplex either the signal Y 4  or the signal Y 5  to the signal Y 3 . The selection between the signal Y 4  and Y 5  is controlled by the signal C 2 . 
         [0064]    The circuit  166  is shown implementing the high pass filter. The circuit  166  is operational to generate the signal Y 5  by high-pass filtering the signal EXP 2 . The circuit  166  provides similar changes in the signal Y 5  as the circuit  168  does in the signal Y 1 . 
         [0065]    The circuit  170  is shown implementing another high pass filter. The circuit  170  is operational to generate the signal Y 4  by high-pass filtering the signal Y 2 . The circuit  70  provides similar changes in the signal Y 4  as the circuit  168  does in the signal Y 1 . 
         [0066]    The circuit  115   a  operates similar to the circuit  115 . In the circuit  115   a , the signal Y 2  and EXP 2  are filtered prior to being multiplexed. The selected filtered signal is presented in the signal Y 3  to the circuit  116 . 
         [0067]    Referring to  FIG. 6 , a block diagram of an example implementation of a circuit  116   a  is shown. The circuit  116   a  is a variation of the circuit  116 . The circuit  116   a  generally comprises a block (or circuit)  180 , a block (or circuit)  182  and a block (or circuit)  184 . The block  164  is optionally removed from the circuit  115   a  such that the signal Y 3  matches the signal Y 5 . The circuits  180  to  184  may represent modules and/or blocks that may be implemented as hardware, software, a combination of hardware and software, or other implementations. 
         [0068]    The signals Y 1  and Y 3  are shown being received by the circuit  180 . The signal Y 1  and a signal Y 4  are received by the circuit  182 . A signal (e.g., E 1 ) is generated by the circuit  180  and transferred to the circuit  184 . A signal (e.g., E 2 ) is generated by the circuit  182  and transferred to the circuit  184 . The signal E is generated and presented by the circuit  184 . 
         [0069]    Each circuit  180  and  182  is shown implementing a subtracter circuit. The circuit  180  is operational to generate a difference between the synthesized echo received in the signal Y 3  and the actual echo as received in the signal Y 1 . The difference is an error value in the signal E 1 . The circuit  182  is operational to generate a difference between the synthesized echo received in the signal Y 4  and the actual echo as received in the signal Y 1 . The difference is an error value in the signal E 2 . 
         [0070]    The circuit  184  is shown implementing a multiplexer circuit. The circuit  184  is operational to generate the signal E by selecting between the signals E 1  and E 2 . Control of the selection may be governed by the signal C 2 . 
         [0071]    In some situations, the data in the signal Y 2  has slight errors because the echo estimate is not completely accurate. Therefore, the erroneous data can be quantized incorrectly. To account for the incorrect quantization, the circuit  180  measures an error between the quantized version of the data in the signal Y 3  and the signal Y 1  while the circuit  182  measures an error between the unquantized version of the data in the signal Y 2  (via the signal Y 4 ) and the signal Y 1 . The circuit  184  receives both errors in the signal E 1  and the alternate signal E 2 , respectively. The circuit  184  is operational to select the signal with the smaller (or lower) error on a sample-by-sample basis and present the selected data in the signal E. 
         [0072]    Double talk in the system  90  is a low probability and/or a limited occurrence. The existence of near-end speech and double talk means that the quantization on the signal SIN is not fully related to the echo production process. To account for the double talk, detection is performed by the circuit  118  in some embodiments. Upon detection to the double talk, the circuits  118  and  164  gate the quantization of the signal Y 2 , and so the multiple inputs to the subtracter circuit  116  will not be used and only the signal E 2  from circuit  182  is calculated. The internal state of the high pass filter is preserved for use with all the possible signals EXP from circuit  162 . 
         [0073]    Referring to  FIG. 7 , a partial block diagram of another example implementation of a circuit  104   a  is shown. The circuit  104   a  generally comprises a block (or circuit)  160   a , a block (or circuit)  162   a , multiple blocks (or circuits)  166   a - 166   n , the block  168 , the block  170 , multiple blocks (or circuits)  180   a - 180   n , the circuit  182 , the circuit  184 , a block (or circuit)  210 , a block (or circuit)  212  and a block (or circuit)  214 . The circuits  160   a  to  214  may represent modules and/or blocks that may be implemented as hardware, software, a combination of hardware and software, or other implementations. 
         [0074]    The signal Y 2  is shown being received by the circuit  160   a . Multiple signals (e.g., CQ−N to CQ+N) are shown being generated by the circuit  160   a  and presented to the circuit  162   a . The circuit  162   a  is shown generating multiple signals (e.g., EXP 2 −N to EXP 2 +N) that are transferred to the circuits  166   a - 166   n , respectively. Multiple signals (e.g., Y 3 −N to Y 3 +N) are shown being generated by the circuits  166   a - 166   n  and transferred to the circuits  180   a - 180   n , respectively. Each circuit  180   a - 180   n  receives the signal Y 1 . Error signals generated by the circuits  180   a - 180   n  are shown being received by the circuits  210  and  212 . A signal (e.g., C 3 ) is shown being generated by the circuit  212  and transferred to the circuit  210 . The signal C 3  is a control signal used to select among the error signals generated by the circuits  180   a - 180   n . The signal E 1  is generated by the circuit  210 . The signals E 1  and E 2  are shown being received by the circuit  214 . The circuit  214  also receives information about a far talker. The circuit  214  generates the signal C 2 . 
         [0075]    The circuit  160   a  is shown implementing a compresser/quantizer circuit. The circuit  160   a  is a variation of the circuit  160 . The circuit  160   a  is operational to compress the data received in the signal Y 2  to generate the signals CQ-N to CQ+N. The compression function includes a quantization of the data per either the A-law technique or the μ-law technique. In some embodiments, the circuit  160   a  creates 2N+1 (e.g., N≧1) outputs from the quantizer producing the multiple signals CQ−N to CQ+N, quantized at levels adjacent to the most likely level chosen by the circuit  160   a  for the signal Y 2 . 
         [0076]    The circuit  162   a  is shown implementing an expander circuit. The circuit  162   a  is a variation of the circuit  162 . The circuit  162   a  is operational to expand the data received in the signals CQ−N to CQ+N to generate the signals EXP 2 −N to EXP 2 +N. The expansion functions generally reverse the compression/quantizing functions performed by the circuit  160   a.    
         [0077]    Each circuit  166   a - 166   n  is shown implementing a high pass filter. Each circuit  166   a - 166   n  may be a copy of the circuit  166 . The circuits  166   a - 166   n  are operational to generate the signals Y 3 −N to Y 3 +N by high-pass filtering the signals EXP 2 −N to EXP 2 +N, respectively. 
         [0078]    Each circuit  180   a - 180   n  is shown implementing a subtracter circuit. Each circuit may be a copy of the circuit  180 . The circuits  180   a - 180   n  are operational to generate differences between the synthesized echos received in the signals Y 3 −N to Y 3 +N and the actual echo as received in the signal Y 1 . The differences are presented to the circuit  210 . 
         [0079]    The circuit  210  is shown implementing a multiplexer circuit. The circuit  210  is operational to generate the signal E 1  by selecting among the differences (error signals) generated by the circuits  180   a - 180   n . Control of the selection may be provided from the circuit  212  via the signal C 3 . 
         [0080]    The circuit  212  is shown implementing a decision logic circuit. The circuit  212  is operational to compare the error magnitudes of the quantized difference signals generated by the circuits  180   a - 180   n  and choose the quantized difference signal with a least error magnitude to use as the signal E 1 , as measured sample-by-sample. The chosen quantized difference signal may be identified to the circuit  210  in the signal C 3 . In some embodiments, the circuit  212  forms part of the circuit  118 . In some embodiments, the signal C 3  forms part of the signal C 2 . 
         [0081]    The circuit  214  is shown implementing another decision logic circuit. The circuit  214  is operational to choose signals E 1  or E 2  with the least error magnitude to use as the signal E, as measured sample-by-sample. The chosen quantized difference signal may be identified to the circuit  184  in the signal C 2 . In some embodiments, the circuit  214  forms part of the circuit  118 . 
         [0082]    The signal Y 2  is presented to the circuit  160   a  and multiple versions of the signals EXP 2 −N to EXP 2 +N are generated by the circuit  162   a . The signal EXP 2  in  FIG. 7  is the same as the signal EXP 2  in  FIGS. 4 and 5 . The other signals EXP 2 −N to EXP 2 −1 and EXP 2 +1 to EXP 2 +N are generated based on the adjacent (different) levels of quantization. Since μ-law quantization and A-law quantization have different quantization steps based on the amplitude of the signal Y 2 , the difference (i) between the values in the signals EXP 2 −1 and EXP 2  and (ii) between the values in the signals EXP 2  and EXP 2 +1 will depend on a value of the signal Y 2 . For instance, if the value in the signal Y 2  is near full amplitude, the adjacent quantization steps will be many (e.g., 1024) units apart for scaling. If the amplitude of the signal Y 2  is rather small, the steps may be a few (e.g., 8) units apart. The number of adjacent steps will typically be odd, allowing for the central signal EXP 2  and steps of ±N on each side (e.g., signals EXP 2 −N to EXP 2 −1 and EXP+1 to EXP+N) 
         [0083]    Each signal EXP 2 −N to EXP 2 +N is transferred to a respective high pass filter (e.g., the circuits  166   a - 166   n ) as one or more internal states of the high pass filters depend on the output for infinite impulse response filter implementations. Each filtered value in the signals Y 3 −N to Y 3 +N is subtracted from a value in the signal Y 1  by the circuits  180   a - 180   n . The values of the resulting errors are compared in the circuit  212  to decide which gives the least error. The signal with the least error is selected by the circuit  212  and multiplexed through the circuit  210  as the signal E 1 . At the same time, the internal states of the particular high pass filter whose output produced the best result is copied to all the other high pass filters, including the high pass filter circuit for Y 2 , in order to provide the best starting state for the next output. 
         [0084]    The logic used for the circuit  214  uses the far talker input to help make the decision as to whether the error signal E 1  will be overridden and thus only the error signal E 2  can be selected. If far talker is true, the signal E 1  or the signal E 2  is selected based on the best performance. If the signal E 2  is chosen based on the far talker or on the best performance, the internal state of the high pass filter for the signal Y 2  is copied to all the other high pass filters. Table I shows the logic used for the decision making for the signal C 2  for both the single and multiple quantizing cases as follows. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE I 
               
             
             
               
                   
                   
               
               
                   
                 Inputs 
                   
                 Output 
               
             
          
           
               
                   
                 Far Talker 
                 Signal E1 
                 Signal E2 
                 Signal C2 
               
               
                   
                   
               
               
                   
                 True 
                 |E1| &lt; |E2| 
                 |E1| &lt; |E2| 
                 Select E1 
               
               
                   
                 True 
                 |E1| &gt; |E2| 
                 |E1| &gt; |E2| 
                 Select E2 
               
               
                   
                 False 
                 Don&#39;t care 
                 Don&#39;t care 
                 Select E2 
               
               
                   
                   
               
             
          
         
       
     
         [0085]    In some embodiments, where the high pass filters are implemented as infinite impulse response filters, the state variables in the high pass filter of each path (e.g., the circuits  166 ,  166   a - 166   n  and the circuit  170 ) should be updated with the variables found in the path producing the best result. The circuit  168  will always have the correct state variables since no decision would affect the content therein. 
         [0086]    Referring to  FIG. 8 , a graph  220  of an example simulation of a best inverse echo return loss enhancement performance is shown. A curve  222  illustrates the best inverse echo return loss enhancement as a function of time. The curve  222  illustrates an inverse echo return loss enhancement performance of less than −38 dB that settles after approximately 4 seconds. An absolute inverse echo return loss enhancement in the simulation is less than −42 dB. A curve  224  illustrates an average inversed echo return loss enhancement performance of the canceller with the quantization compensation turned on. The average inversed echo return loss enhancement performance approaches −47 dB of cancellation by selecting between Y 2  and Y 3 . The performance simulation provides better than 60 dB, reduction in echo, using three or more quantization levels. 
         [0087]    The functions performed by the diagrams of  FIGS. 1-7  may be implemented using one or more of a conventional general purpose processor, digital computer, microprocessor, microcontroller, RISC (reduced instruction set computer) processor, CISC (complex instruction set computer) processor, SIMD (single instruction multiple data) processor, signal processor, central processing unit (CPU), arithmetic logic unit (ALU), video digital signal processor (VDSP) and/or similar computational machines, programmed according to the teachings of the specification, as will be apparent to those skilled in the relevant art(s). Appropriate software, firmware, coding, routines, instructions, opcodes, microcode, and/or program modules may readily be prepared by skilled programmers based on the teachings of the disclosure, as will also be apparent to those skilled in the relevant art(s). The software is generally executed from a medium or several media by one or more of the processors of the machine implementation. 
         [0088]    The invention may also be implemented by the preparation of ASICs (application specific integrated circuits), Platform ASICs, FPGAs (field programmable gate arrays), PLDs (programmable logic devices), CPLDs (complex programmable logic devices), sea-of-gates, RFICs (radio frequency integrated circuits), ASSPs (application specific standard products), one or more monolithic integrated circuits, one or more chips or die arranged as flip-chip modules and/or multi-chip modules or by interconnecting an appropriate network of conventional component circuits, as is described herein, modifications of which will be readily apparent to those skilled in the art(s). 
         [0089]    The invention thus may also include a computer product which may be a storage medium or media and/or a transmission medium or media including instructions which may be used to program a machine to perform one or more processes or methods in accordance with the invention. Execution of instructions contained in the computer product by the machine, along with operations of surrounding circuitry, may transform input data into one or more files on the storage medium and/or one or more output signals representative of a physical object or substance, such as an audio and/or visual depiction. The storage medium may include, but is not limited to, any type of disk including floppy disk, hard drive, magnetic disk, optical disk, CD-ROM, DVD and magneto-optical disks and circuits such as ROMs (read-only memories), RAMs (random access memories), EPROMs (erasable programmable ROMs), EEPROMs (electrically erasable programmable ROMs), UVPROM (ultra-violet erasable programmable ROMs), Flash memory, magnetic cards, optical cards, and/or any type of media suitable for storing electronic instructions. 
         [0090]    The elements of the invention may form part or all of one or more devices, units, components, systems, machines and/or apparatuses. The devices may include, but are not limited to, servers, workstations, storage array controllers, storage systems, personal computers, laptop computers, notebook computers, palm computers, personal digital assistants, portable electronic devices, battery powered devices, set-top boxes, encoders, decoders, transcoders, compressors, decompressors, pre-processors, post-processors, transmitters, receivers, transceivers, cipher circuits, cellular telephones, digital cameras, positioning and/or navigation systems, medical equipment, heads-up displays, wireless devices, audio recording, audio storage and/or audio playback devices, video recording, video storage and/or video playback devices, game platforms, peripherals and/or multi-chip modules. Those skilled in the relevant art(s) would understand that the elements of the invention may be implemented in other types of devices to meet the criteria of a particular application. 
         [0091]    The terms “may” and “generally” when used herein in conjunction with “is(are)” and verbs are meant to communicate the intention that the description is exemplary and believed to be broad enough to encompass both the specific examples presented in the disclosure as well as alternative examples that could be derived based on the disclosure. The terms “may” and “generally” as used herein should not be construed to necessarily imply the desirability or possibility of omitting a corresponding element. 
         [0092]    While the invention has been particularly shown and described with reference to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the scope of the invention.