Acoustic Echo Cancellation

Echo cancellation has been a problem since the early days of telephone technology. It arises whenever the backward and forward transmission lines are not completely separated, allowing some signal leakage. This may happen because of the impedance mismatch in the hybrid coil circuit before the connection to the telephone set (line echo). Acoustic echo cancellation (AEC) in hands-free system may be caused by the acoustic coupling between the loudspeaker and the microphone in the receiving room. In AEC systems, the measured microphone signal contains two signals: the far-end echoed signal and the near-end signal. The goal is to remove the former from the latter so that only the desired near-end signal is played by the loudspeaker. Nowadays, there is a large interest towards multimedia teleconferencing systems because of the increasing requirement for efficient communications and the development of advanced digital signal processing techniques. As a matter of fact, multichannel systems have become essential in order to reduce undesired echoes and to introduce better performance in terms of sound localization in the presence of more than one participant. Already, stereophonic systems and, thus, stereophonic acoustic echo cancellers, obtain realistic performance, since listeners have spatial information that helps to identify the speaker position. Unfortunately, more echo patterns have to be identified and the linear relationship existing between the two channels generated from the same source brings to the so-called nonuniqueness problem. The covariance matrix results very ill-conditioned and the solution of the normal equation depends on the speaker position in the transmission room, which is not stationary, causing possible convergence problems due to room changes. Therefore, a method to reduce interchannel coherence must be introduced in order to obtain good echo cancellation performance still preserving audio quality. Moreover, this relation affects also the choice of the adaptive filtering algorithm. Thus, algorithms that do not take into consideration the cross-correlation among channels could converge very slowly. As a matter of fact, adopting straightforward extensions of single channel algorithms is not the best solution. In addition, to outperform the difficult choice of the step-size in the adaptation, variable step-size-based approaches can be introduced aiming at solving the trade-off between faster convergence and lower steady-state performance.

In this field, A3LAB research is mainly focused on the study of psychoacoustic solutions to the nonuniqueness problem and also on the analysis and development of different echo acoustic cancellation algorithms in real-world scenarios. 

Related projects

• TASCA

Related pubblications

1. L Romoli, S Cecchi and F Piazza. A Novel Decorrelation Approach for Multichannel System Identification. In Proc. IEEE International Conference on Acoustics, Speech and Signal Processing. May 2014, . BibTeX

   @inproceedings{romoli-icassp-14,
   	title = "{A Novel Decorrelation Approach for Multichannel System Identification}",
   	author = "Romoli, L. and Cecchi, S. and Piazza, F.",
   	booktitle = "Proc. {IEEE} International Conference on Acoustics, Speech and Signal Processing",
   	address = "Florence, Italy",
   	year = 2014,
   	month = "May",
   	pages = ""
   }
   

2. L Romoli, S Cecchi and F Piazza. Channel Decorrelation in Stereo Acoustic Echo Cancellation exploiting Missing-Fundamental Theory and Frequency Shifting. IEEE Signal Process. Lett. 20(7):717-720, 2013. BibTeX

   @article{romoli-spl-13,
   	author = "Romoli, L. and Cecchi, S. and Piazza, F.",
   	title = "{Channel Decorrelation in Stereo Acoustic Echo Cancellation exploiting Missing-Fundamental Theory and Frequency Shifting}",
   	journal = "{IEEE} Signal Process. Lett.",
   	volume = 20,
   	number = 7,
   	note = "{DOI = 10.1109/LSP.2013.2264936}",
   	month = "Jul.",
   	year = 2013,
   	pages = "717-720"
   }
   

3. L Romoli, S Cecchi and F Piazza. Evaluation of a Channel Decorrelation Approach for Stereo Acoustic Echo Cancellation. In Int'l Symposium on Image and Signal Processing and Analysis . 2013, . BibTeX

   @inproceedings{romoli-ispa-13,
   	title = "{Evaluation of a Channel Decorrelation Approach for Stereo Acoustic Echo Cancellation}",
   	author = "Romoli, L. and Cecchi, S. and Piazza, F.",
   	booktitle = "Int'l Symposium on Image and Signal Processing and Analysis",
   	volume = "",
   	address = "Trieste, Italy",
   	month = "Sep.",
   	year = 2013,
   	pages = ""
   }
   

4. S Cecchi, L Romoli, P Peretti and F Piazza. Low-complexity implementation of a real-time decorrelation algorithm for stereophonic acoustic echo cancellation. Signal Processing 92(11):2668-2675, 2012. BibTeX

   @article{cecchi-jsp-12,
   	author = "Cecchi, S. and Romoli, L. and Peretti, P. and Piazza, F.",
   	title = "{Low-complexity implementation of a real-time decorrelation algorithm for stereophonic acoustic echo cancellation}",
   	journal = "Signal Processing",
   	volume = 92,
   	number = 11,
   	pages = "2668-2675",
   	year = 2012,
   	month = "Nov."
   }
   

5. M Pirro, S Squartini, L Romoli and F Piazza. Stereophonic Hands-Free Communication System based on Microphone Array Fixed Beamforming: Real-Time Implementation and Evaluation. J. Audio, Speech, Music Processing, 2012. BibTeX

   @article{pirro-jamsp-12,
   	author = "Pirro, M. and Squartini, S. and Romoli, L. and Piazza, F.",
   	title = "{Stereophonic Hands-Free Communication System based on Microphone Array Fixed Beamforming: Real-Time Implementation and Evaluation}",
   	journal = "J. Audio, Speech, Music Processing",
   	note = "{DOI = 10.1007/s11760-012-0387-0}",
   	year = 2012,
   	month = "Oct."
   }
   

6. L Romoli, S Cecchi, P Peretti and F Piazza. A Mixed Decorrelation Approach for Stereo Acoustic Echo Cancellation based on the estimation of the fundamental frequency. IEEE Trans.~Audio, Speech and Language Processing 20(2):690-698, 2012. BibTeX

   @article{romoli-jasl-11,
   	author = "Romoli, L. and Cecchi, S. and Peretti, P. and Piazza, F.",
   	title = "{A Mixed Decorrelation Approach for Stereo Acoustic Echo Cancellation based on the estimation of the fundamental frequency}",
   	journal = "IEEE Trans.~Audio, Speech and Language Processing",
   	volume = 20,
   	number = 2,
   	pages = "690-698",
   	year = 2012,
   	month = "Feb."
   }
   

7. S Cecchi, L Romoli, P Peretti and F Piazza. A Combined Psychoacoustic Approach for Stereo Acoustic Echo Cancellation. IEEE Trans.~Audio, Speech and Language Processing 19(6):1530-1539, 2011. BibTeX

   @article{cecchi-jasl-10,
   	author = "Cecchi, S. and Romoli, L. and Peretti, P. and Piazza, F.",
   	title = "{A Combined Psychoacoustic Approach for Stereo Acoustic Echo Cancellation}",
   	journal = "IEEE Trans.~Audio, Speech and Language Processing",
   	volume = 19,
   	number = 6,
   	pages = "1530-1539",
   	year = 2011,
   	month = "Nov."
   }
   

8. L Romoli, S Squartini and F Piazza. A Variable Step-Size Frequency-Domain Adaptive Filtering Algorithm for Stereophonic Acoustic Echo Cancellation. In Proc. 18th # "European Signal Processing Conference" . 2010, 26-30. BibTeX

   @inproceedings{romoli-"European Signal Processing Conference"-10,
   	title = "{A Variable Step-Size Frequency-Domain Adaptive Filtering Algorithm for Stereophonic Acoustic Echo Cancellation}",
   	author = "Romoli, L. and Squartini, S. and Piazza, F.",
   	booktitle = {{Proc. 18th } # "European Signal Processing Conference"},
   	volume = "",
   	address = "Aalborg, Denmark",
   	month = "Aug.",
   	year = 2010,
   	pages = "26-30"
   }
   

9. L Romoli, S Cecchi, L Palestini, P Peretti and F Piazza. A Novel Approach to Channel Decorrelation for Stereo Acoustic Echo Cancellation based on Missing Fundamental Theory. In Proc. IEEE International Conference on Acoustics, Speech and Signal Processing. 2010, 329-332. BibTeX

   @inproceedings{romoli-icassp-10,
   	title = "{A Novel Approach to Channel Decorrelation for Stereo Acoustic Echo Cancellation based on Missing Fundamental Theory}",
   	author = "Romoli, L. and Cecchi, S. and Palestini, L. and Peretti, P. and Piazza, F.",
   	booktitle = "Proc. {IEEE} International Conference on Acoustics, Speech and Signal Processing",
   	address = "Dallas, TX, USA",
   	year = 2010,
   	month = "Mar.",
   	pages = "329-332"
   }
   

10. L Romoli, S Cecchi, P Peretti and F Piazza. Improved Approach to Stereophonic Channel Decorrelation based on missing fundamental theory. In Proc. Workshop on Acoustic Echo and Noise Control . 2010, 1-4. BibTeX

    @inproceedings{romoli-iwaenc-10,
    	title = "{Improved Approach to Stereophonic Channel Decorrelation based on missing fundamental theory}",
    	author = "Romoli, L. and Cecchi, S. and Peretti, P. and Piazza, F.",
    	booktitle = "Proc. Workshop on Acoustic Echo and Noise Control",
    	volume = "",
    	address = "Tel Aviv, Israel",
    	month = "Sep.",
    	year = 2010,
    	pages = "1-4"
    }
    

11. S Cecchi, L Romoli, P Peretti and F Piazza. A Real Time implementation of a Novel Psychoacoustic Approach for Stereo Acoustic Echo Cancellation. In Proc. 129th # "Audio Engineering Society Convention" . 2010, . BibTeX

    @inproceedings{cecchi-aes-10,
    	title = "{A Real Time implementation of a Novel Psychoacoustic Approach for Stereo Acoustic Echo Cancellation}",
    	author = "Cecchi, S. and Romoli, L. and Peretti, P. and Piazza, F.",
    	booktitle = {{Proc. 129th } # "Audio Engineering Society Convention"},
    	volume = "",
    	address = "San Francisco, CA, USA",
    	month = "Oct.",
    	year = 2010,
    	pages = ""
    }