This noise reduction block removes background noise and therefore improves the signal to noise ratio of the transmit signal. The residual signal is fed to the noise reduction block. The adaptive filter estimates the echo and subtracts it from the TxIn signal to form the residual signal. The output of the bulk delay is fed to the adaptive filter. The bulk delay block compensates for the buffering delay at the RxOut and TxIn interfaces as well as any other non-acoustic system delays in the path between RxOut and TxIn. The output of the RxNLP is fed both to the transmit output (TxOut) and into the bulk delay block. Under difficult acoustic conditions, the RxNLP can improve full-duplex operation and hence the overall voice quality. The RxIn signal coming from the network is fed into the RxNLP (Receive Nonlinear Processor). The names receive and transmit are used from the point-of-view of the person at the speaker/microphone side. The terms Rx (Receive) and Tx (Transmit) may be confusing at first because both the receive and transmit paths have inputs and outputs. Detection of double-talk is vital to the performance of an acoustic echo canceller. Double talk occurs when the speech of two talkers overlap causing the audio signals to arrive simultaneously at the echo canceller. Adaptive Digital’s HD AEC analyses the signal in as finite a period as is possible to best develop the echo model, and then cancels the echo immediately. This number can never be “0” as analyzing the signal is a critical part of the echo cancellation process.
HD AEC electronically removes both direct coupling and reflected echo, enabling true full-duplex hands-free telephony.Ĭonvergence time is the time it takes the echo cancel algorithm to analyze the signal. With Anti-howling enabled the HD AEC identifies when instability is starting to occur and takes action to mitigate the instance of feedback looping. In full-duplex communication systems where, by definition, both communication paths are open at all time, howling can be a serious issue. These echo, or coupling, paths create feedback loops.
Howling can occur when there is a full-duplex communication link with echo at both ends. The AGC algorithm is used to automatically adjust the speech level of an audio signal so that the level falls within a user-defined output level range. Changes in gain can adversely affect an AEC Adaptive Digital’s HD AEC has the ability to adapt to changes in the acoustic path (including gain/loss changes.) And when the changes are known, like in the case of controlled gain changes, Adaptive Digital’s HD AEC has hooks that enable the application to tell it the nature of the gain change so it can adjust immediately rather than take time to reconverge.Īutomatic Gain Control (AGC) is provided to help boost lower level speech signals in hands-free environments. By making the AGC aware of the AEC state, we can avoid having the AGC becoming a cause of howling. Noise Reduction is done pre-NLP, resulting in a far cleaner audio stream feeding into the non-linear processor. *NR2 is not turned on.Īdaptive Digital Technologies’ high definition acoustic echo canceller ( HD AEC), has integrated Noise Reduction and AGC into its AEC algorithm and created appropriate hooks to make them work together seamlessly. Note: MIPS generated with AGC, NR and CNG enabled. HD AEC C55x CPU Utilization & Memory Requirements HD AEC C64x / C64x+ CPU Utilization & Memory Requirements When using external source for program and data memory, MIPS increase by 3x per enabled microphone. Note: MIPS generated with single mic enabled, and running with on chip (internal) program and data memory only. HD AEC C674x CPU Utilization & Memory Requirements HD AEC ARM Cortex-M7 CPU Utilization & Memory Requirements
#Acoustic echo cancellation series#
Specifications measured on TI Tiva C series ARM Cortex-M4 based MCU. Note: HD AEC Cortex-M4 MIPS generated with 0 wait state FLASH. HD AEC ARM Cortex-M4 CPU Utilization & Memory Requirements Specifications measure on BeagleBoard-xM TI AM37x ARM Cortex-A-8 based MCU. Note: MIPS generated with single mic enabled,running with on chip (internal) program and data memory only. HD AEC ARM Cortex-A8/A9/A15/A17 CPU Utilization & Memory RequirementsĪll Memory usage is given in units of byte.