A joint echo cancellation algorithm for quick suppression of howls in hearing aids

Abstract

When the echo path of a hearing aid suddenly changes, howls easily occur. To quickly suppress the howls, a joint echo cancellation (JEC) algorithm, which combines the variable step normalized least mean square (VNLMS) algorithm with the notch filter algorithm, is proposed. According to whether the hearing aid howls or not, different strategies are used. First, when there are no howls, the echo signal is estimated using VNLMS and the step factor is computed according to three types of filter states, which are defined based on the normalized distance between the short-term average and the long-term average of the filter coefficients. Then, different step factors are used for different states. Second, when there are howls, the update of VNLMS is frozen to stabilize the howl frequency. To improve the detection accuracy, a howling detection algorithm based on the zoom-fast Fourier transformation (ZoomFFT) is proposed. The ZoomFFT algorithm can analyze the spectrum of a narrowband signal in a specified high sampling frequency. Then, the notch filters based on the estimated howl frequencies are dynamically generated to restrain the howls. Finally, when the howls are suppressed, VNLMS is reactivated. Compared to other echo cancellation algorithms, the proposed algorithm can quickly suppress the howls, and JEC has the best comprehensive performance. Furthermore, the quality of the processed speech is high, and the operation time is short. Thus, the proposed algorithm is suitable for low-power-consumption and small-volume products such as hearing aids.

Howling Detection and Suppression Based on Segmented Notch Filtering

“…To compensate for the loss arising from the occasional howling, one mainstream approach is to add an adaptive filter based loop inside the hearing aid (proposed by [ 15 ]), as illustrated in Figure 2 .…”

“…To overcome the limitations of the adaptive echo cancellation method and achieve a better howling cancellation, many researchers incorporated the notch filtering technique into the adaptive filtering scheme. For example, Liang [ 15 ] combines the variable step normalized least mean square(VNLMS) algorithm with the notch filter algorithm to quickly suppress the howling. A. Sogami [ 16 ] proposed a howling canceller, which cancels howling by using a cascade notch filter designed from a distance between a loudspeaker and a microphone.…”

Dual-Microphone Speech Reinforcement System With Howling-Control for In-Car Speech Communication

“…The proposed SR system is tested by computer simulations via Matlab. The train and test speech signals are composed (without repetition) from TIMIT speech database (Zue et al, 1990), as in (Liang et al, 2017), and the sampling frequency is 16 kHz. A constant system processing delay of 5 ms was inserted in simulations, considering that it must be short enough so the listener does not notice the time difference between the direct (spoken) and emitted (reinforced) sound signals.…”

“…Several approaches to deal with the disruptive howling effect have been proposed. A common approach for preventing electroacoustic coupling, also utilized in hearing aids (Nakagawa et al, 2012;Liang et al, 2017), is to use an acoustic echo canceller (AEC). An AEC consists of an adaptive filter that aims at canceling the echo signal from the loudspeaker by adjusting itself to the room-impulse-response (RIR) of the LEM-path (Shynk et al, 1992;Ortega et al, 2005;Reuven et al, 2007;Cifani et al, 2009;Cohen et al, 2009;Van Waterschoot and Moonen, 2010;Nakagawa et al, 2012;Bulling et al, 2016).…”