Abstract
When designing closed-loop electro-acoustic systems, which can commonly be found in hearing aids or public address systems, the most challenging task is canceling and/or suppressing the feedback caused by the acoustic coupling of the transducers of such systems. In many applications, feedback cancelation based on adaptive filters is used for this purpose. However, due to computational complexity such a feedback canceler is often limited in the length of the filter’s impulse response. Consequently, a residual feedback, which is still audible and may lead to system instability, remains in most cases. In this work, we present enhancements for model-based postfilters based on a priori knowledge of the feedback path which can be used cooperatively with the adaptive filter-based feedback cancelation system to suppress residual feedback and improve the overall feedback reduction capability. For this, we adapted an existing reverberation model such that our model additionally considers the presence and the performance of the adaptive filter. We tested the effectiveness of our approach by means of both objective and subjective evaluations.
Highlights
Signal processing in a closed electro-acoustic loop is a challenging task
4 Model-based feedback suppression as postfilter Due to stability reasons, finite impulse response (FIR) filters are commonly used in adaptive filter applications like echo- or feedback cancelation. If this kind of method is used in a closed electroacoustic loop system, it is capable of subtracting parts of the feedback signal r(n) from the microphone signal y(n) depending on how good it is adapted to the true room impulse response
An easier method compared to models B and C is to assume that the adaptive filter operates perfectly well and there is only the length limitation which has to be covered by the postfilter
Summary
Signal processing in a closed electro-acoustic loop is a challenging task. It occurs in various applications such as hearing aids [1, 2], public address (PA) systems [3, 4] or so-called in-car communication (ICC) systems [5, 6]. Impulse response hLM,i as well as the part h LM,i that an adaptive filter has estimated. A different method to increase the stability gain in electro-acoustic loops is to estimate the short-term power spectral density (PSD) of the feedback by using the energy envelopes of the room’s subband impulse responses.
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