EC Types & Applications
- Acoustic Echo Canceller
A discussion of how an Acoustic Echo Canceller can remove audible echoes caused by acoustic coupling and acoustic reverberation - Line/Network Echo Canceller
A discussion of how line/network cancellers can remove audible echoes caused by telephone hybrid circuits - Line and Acoustic Echo Canceller Combined
A discussion of echo cancellers that handle both line echo and acoustic echo - Far-end Echo Canceller
A discussion of how an Acoustic Echo Canceller can remove audible echoes received from the far-end speaker - Stereo Acoustic Echo Canceller
A discussion of acoustic echo cancellers used with audio conferencing and surround sound systems - Acoustic Echo Cancellation (AEC) for Commercially Available Off-the-Shelf (COTS) Hardware
A discussion of acoustic echo cancellation solutions for use with COTS hardware. - Non-conventional Applications of Acoustic Echo Cancellation (AEC)
Acoustic echo cancellation can be applied to any voice communication system to achieve high quality full-duplex conversations. - Stereophonic Acoustic Echo Cancellation
A discussion of stereophonic acoustic echo cancellation - Wideband Acoustic Echo Cancellation
A discussion of acoustic echo cancellation (AEC) used in wideband audio teleconferencing where the presence of the acoustic echoes in the microphone signal cause significant degradation in the quality of conversation. - Subband Acoustic Echo Cancellation
Subband adaptive filtering overcomes many of the limitations of traditional time-domain normalized least means squares implementations of echo cancellation. - VoIP Echo Cancellation
A discussion of echo cancellation in VoIP networks - Echo Cancellation Software in VoIP Gateways
A discussion of handling echoes generated in the transmission path. - Echo Cancellation in Cellular Networks
There are several cellular network architectures which influence the implementation of an echo canceller. - Frequency Domain Adaptive Filtering in Echo Cancellation
Frequency Domain Adaptive Filters (FDAF) in acoustic echo cancellation applications provide several advantages over its time domain counterpart. - Tandem Echo Cancellers
Discussion of echo cancellers connected in tandem used in networking and voice enhancement. - Acoustic Echo Cancellation with Expanded Dynamic Range
Discussion of echo cancellers with extended dynamic range
Adaptive Filters
- FIR Filter Design
Discussion of FIR filter design using suboptimal and optimal methods - High-Pass Filters in Echo Cancellers
Discussion of high-pass filters used in echo cancellation to achieve expected product performance. - Echo Cancellation based on Adaptive IIR Filtering
Discussion of the advantages of adaptive IIR filtering used in echo cancellation. - Line Echo Canceller with Backup FIR Filter
Discussion on using a second FIR filter with the FIR adaptive filter in applications where the echo path is relatively constant. - Linear Phase Filters in Acoustic Echo Cancellation
A discussion of linear phase filters used in acoustic echo cancellation. - Acoustic Echo Cancellation for Sparse Echo Paths
How the Proportionate NLMS algorithm can be used to process sparse echo paths in acoustic echo cancellation. - Variable Tap Length Filters for Acoustic Echo Cancellation
A discussion of managing conflicting requirements of fast convergence and full echo cancellation. - Two-Path Method for Acoustic Echo Cancellation
Discussion on AEC using a two-path method to mitigate the acoustic coupling between the loudspeaker and microphone for achieving full-duplex communication in audio conferencing systems. - Particle Swarm Optimization in the Design of Adaptive FIR Filters
Particle Swarm Optimization in the Design of Adaptive FIR Filters. - Particle Swarm Optimization in the Design of Adaptive IIR Filters
Particle Swarm Optimization in the Design of Adaptive IIR Filters. - Kalman Filter in Acoustic Echo Cancellation
A discussion of Kalman filters used in acoustic echo cancellation - Gammachirp Filter for Acoustic Echo Cancellation
A discussion of Gammachirp filters used in acoustic echo cancellation - Haar Wavelet Decomposition in Acoustic Echo Cancellation
A discussion of multi-resolution analysis in acoustic echo cancellation - Viterbi Algorithm in Speech Enhancement and HMM
Discussion on applications of the Viterbi algorithm to speech enhancement and other technologies - Volterra AEC
A discussion of non-linear aspects of the echo path and representation using a Volterra series. - Critically Sampled Uniform Sub-Band Echo Cancellation using LMS-type Algorithms
A discussion of subband sampling methods with LMS algorithms. - Octave Banks for Acoustic Filtering
A discussion on the use of octave banks with acoustic filters - Acoustic Echo Cancellation (AEC) for Sparse Echo Paths
Method for capturing essential information from a sparse echo path while leaving other information for echo suppression in an acoustic echo cancellation system. - Sparse Echo Cancellers
A discussion of handling echo path impulse responses that are relatively short with sparsely distributed clusters of high energy
EC Features & Filter Control
- Comfort Noise Generation in Echo Cancellers
A discussion of CNG functionality used with echo cancellation to improve the far-end listener experience - Double-Talk Detection in Echo Cancellation
The presence of the near-end talker during far-end speech is a source of disruption in the adaptation of the filter. Adaptation of the filter must be prevented via a double-talk detector. - Tone Detectors in Echo Cancellers
Discussion on how harmonic excitation can impact convergence of the echo canceller adaptive filter. - Line Echo Canceller with Bulk Delay Compensation
Bulk delay compensation can be used for access network configurations with signal delays between the line echo canceller and hybrid circuit ports. - Hidden Markov Models in Acoustic Echo Cancellation
A discussion of hidden Markov models used in acoustic echo cancellation - Signal De-Correlation
Discussion of advantages of signal de-correlation in different applications - Cross-Correlations in Echo Cancellation
The cross-correlation between various signal components can be revealing to the state of the echo canceller. - Stability Control by Echo Canceller
Discussion of echo canceller’s adaptive filtering and stability control in the open and closed loop systems - Potential Instability of NE/FE System with Echo Cancellation
Discussion on stability analysis of Near-End/Far-End systems with echo cancellation - Potential Instability of NE/FE System without Echo Cancellation
Discussion on stability analysis of Near-End/Far-End systems without echo cancellation - Adaptive Filter Algorithm Stability
Discussion on controlling adaptive filter algorithm stability during initial adaptation. - Nonlinear Acoustic Echo Cancellation
A discussion of non-linear acoustic echo canceller design - The Combined Reduction of Echo and Noise
Tackling noise reduction and residual echo reduction in a joint effort. - Post Filtering for Residual Echo Control
Post filtering of echo cancellation systems is important for environments with large levels of non-linear distortion. - Variable Step-size and Regularization Parameters for NLMS
In echo cancellation, proper control of step-size and regularization parameters of the NLMS can improve the overall performance of the system. - Frequency Offset Compensation in Echo Cancellation
Frequency offset in echo cancellation refers to when the sampling frequency of the far-end and near-end signals are not the same. - Aligning Audio Streams Captured using Unsynchronized Clocks
When using multiple data collection devices that are not driven by the same master clock, audio streams must be aligned for testing audio algorithms. - Dynamic Time Warping
Aligning two sequences of feature vectors by warping the time axis - Psychoacoustic Echo Cancellation
Understanding perception of echo can improve acoustic echo cancellation. - Echo Control on Codec Parameters
Direct modification of codec parameters provides a low complexity solution to voice quality enhancement in cellular networks. - Statistical Joint Control of Acoustic Echo Canceller and Post-Filter
Based on statistical properties of the adaptive filter, the echo canceller step-size and the post-filter can be controlled jointly.
Challenges of EC
- Non-Linear AEC
Discussion of acoustic echo path non-linearities limiting AEC performance - Handling of Nonlinearities in Echo Cancellation
A discussion on how an adaptive filter reacts to non-linear distortions. - The Challenges of Stereophonic\Multichannel Echo Cancellation’s
As in all acoustic hands-free communications systems, acoustic echo cancellation is a requirement. Multichannel echo cancellation provides an additional set of signal processing challenges as compared to monophonic echo cancellation. - Acoustic Echo Paths Characteristics and AEC
A discussion of AEC handling of acoustic echo path delays, early reflections and late reflections, echoes related to non-linear distortions. - Echo in Voice over IP Networks
Discussion of reasons to deploy echo cancellers in VoIP networks contrasted with their use in PSTN. - Perception of Echo
How round trip delay and bandwidth influence the perception of echoes. - Critical Distance
A discussion of critical distance for positioning loudspeakers and microphones when designing a sound or a control room. - Critical Distance and RT60
Discussion of method for estimating critical distance for room reverberation - Controlling RT60 – Practical Notes
Discussion of controlling RT60 when evaluating speech enhancement devices - Echo Cancellation with Dereverberation
A discussion of the effect of dereverberation processing combined with echo cancellation. - Echo Cancellation in IP Networks
The implementation of Voice over IP (VoIP) networks, presents a new set of challenges in
optimizing the voice quality and providing the expected toll quality. - The Affect of Convergence Speed in the Two-Path Method
The Affect of Convergence Speed in the Two-Path Method. - Fixed Point Mathematics for Acoustic Echo Cancellation
How fixed point mathematics can improve acoustic echo cancellation performance - Basic Linear Algebra Subprograms (BLAS) in C
Examples of dot product, matrix multiplication, and matrix matrix multiplication using CBLAS Library
Estimation
- Methods of RT60 Estimation
A discussion of methods to estimate RT60 to characterize room reverberation effects. - Practice of RT60 Estimation in Bands
Discussion of methods to estimate room reverberation in subbands - Estimating Echo Return Loss and Echo Return Loss Enhancement
To achieve an ubiquitous solution for an acoustic echo cancellation system, an adaptive filter control system for the echo canceller and the post-filter is required. - Estimating ERL from AF FIR Taps
Method for estimating the ERL value of the echo path using the adaptive filter FIR taps. - Room Impulse Response
A discussion on estimating the room impulse response, i.e. the transfer function between the sound source and microphone. - Impulse Response Estimation for Audio via Complementary Sequences
Use of complementary sequences for impulse response estimation of audio devices and acoustic systems to minimize adverse effects of background noise. - A and C Weighting via Bilinear Transform
Discussion on the standard weighting curves for unbiased digital filtering using bilinear transformation
Testing
- G.168 Test Methodology
Discussion of details pertaining to LEC/NEC testing methodology - G.168 Defined Echo Path Models
A discussion of evaluating any line/network echo canceller when using a laboratory setup - Energy and Level Estimation for G.168 Testing
Methods of signal energy/level estimation for G.168 compliance testing. - Line and Acoustic Echo Diagnostics
Diagnosing and debugging methods to determine what contributes most to the presence of echo for a given system configuration and acoustic scenario. - Equalization For ETSI-Compliant Audio Facility
Discussion for setup of an audio testing facility for acoustical evaluation of audio designs and products - ETSI Audio Room Equalization – Selected Details
Discussion on frequency band selection and the equalization process used for audio facility setup. - Minimum Phase LTI Systems in Context of Equalization
A discussion of how a direct-inverse method can be used to equalize minimum phase LTI systems. - Echo Path Delay Identification Offline
Method to independently estimate the echo path delay with high degree of confidence. - Level Measurements via ITU P56 and Weightingg
Discussion of practices for measuring audio signals - Echo Paths for Hands-Free Terminals
Discussion on ITU P.340 and modeling echo paths for hands free terminals.
EC & Noise Reduction
- Robust Adaptive Algorithms for Echo Cancellation
An acoustic echo canceller may need to address different acoustic and noise control environment issues. Constraints include the volume of the enclosure, the required bandwidth, and the tolerable delay. - Forensic Speaker Recognition Preprocessor
Discussion on using speech preprocessing to improve speech recognition rates in ASR and other applications. - The Combination of Adaptive Filters
An acoustic echo canceller may need to address different acoustic and noise control environment issues. Constraints include the volume of the enclosure, the required bandwidth, and the tolerable delay. - Comb Filtering in Acoustics
A discussion of the comb filtering effect, caused by the position of a loudspeaker, that can impact the listener’s experience. - More on Observations Regarding Musical Noise
Discussion of musical noise and its characteristics - Synthetic Noise for Voice Enhancement
Discussion of synthetic random noise signals used in Voice Enhancement during development, verification and testing - Synthetic Noise of Predefined Spectrum for Voice Enhancement
Methods for generating random noise signals with a predefined spectrum for Voice Enhancement - Blind Source Separation for Noise Reduction in Mobile
Blind Source Separation or Independent Component Analysis is a multi-channel technique that can be used for noise reduction/cancellation in Mobile Telecommunications, such as cell phones and tablets
Speech Dereverberation
- Speech Dereverberation using Channel Inversion and Equalization
A discussion of channel inversion and equalization techniques used to dereverberate speech. - Dereverberation using Spectral Subtraction
A discussion on methods to remove reverberation from received speech signals - Voice Activity Detection for Dereverberation
A discussion of using VAD to estimate the speech reverberation time. - Combination of Dereverberation and Adaptive Beamforming
A discussion on combining dereverberation and beamforming algorithms. - Various Models of Room Reverberation
A discussion of different room models used for speech enhancement device evaluation during development - Reverberation Cancellation Versus Suppression
A discussion of different techniques for handling reverberation.