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Adaptive feedback cancellation is an audio feedback cancellation method commonly used in hearing aids, which uses an adaptive filter (an algorithm unique to adaptive feedback cancellation) to cancel feedback from an acoustic device. [1] Feedback is defined as a system of inputs and outputs creating a feedback loop. Audio feedback (a positive feedback loop) is responsible for screeching noises heard from speakers and hearing aids limiting acoustic gain. Adaptive feedback cancellation uses an adaptive filter to cancel the total mechanical and audio feedback from a microphone, providing clearer sound and allowing more gain. Research in adaptive feedback cancellation has played a role in the advancement of hearing aids, and has the potential to impact the smartphone and computer industry. [2] [3]
History[edit]
Adaptive feedback cancellation originated during the evolution of the hearing aid. The hearing aid became digital, and as such feedback cancellation was needed. In 1980 a directional microphone was introduced in the digital hearing aid, and adaptive feedback cancellation was created to block external noise that the microphone picked up. Today, adaptive feedback cancellation is in nearly every digital hearing aid and current research is still ongoing.[4]
Phases[edit]
Adaptive feedback cancellation follows the following process:
- The process begins with background noise picked by a microphone getting amplified by a speaker in that same device.
- This noise is audio feedback which is stored to later be cancelled
- An adaptive filter uses an algorithm to maximize the amount of the stored audio feedback that can be cancelled
- The adaptive filter is implemented in an acoustic device, and the repetition of this process is adaptive feedback cancellation.
Applications[edit]
Hearing Aids[edit]
Hearing aids use adaptive feedback cancellation to improve the amount of gain. When hearing aids are misplaced or turned to loud volumes they can have large feedback. Noise picked up through the hearing aid's microphone creates this feedback, which is then amplified creating a ringing noise. Adaptive feedback cancellation cancels the noise with an adaptive filter. The product of the adaptive filter cancels the feedback from the microphone creating clear sound from the hearing aid.[5]
Echo Cancellation[edit]
Echo cancellation is a form of adaptive feedback cancellation used in telephones and teleconferencing devices. Much like adaptive feedback cancellation in hearing aids, echo cancellation uses an adaptive filter to cancel echo reverberations from a microphone.[6]
Jammer Suppression[edit]
Jammer suppression is a way to reject interference with large signals that are much stronger than traditional signals. This process uses an adaptive filter, and its algorithm has applications in all types of signal suppression.[7]
Current Research[edit]
Prediction Error Method[edit]
Prediction error method is an adaptive feedback cancellation algorithm that focuses on using audio signals instead of speech signals. This change proposes to improve adaptive feedback cancellation in objects like hearing aids and other audio applications. This approach works closely with echo cancellation, and looks to bring the techniques in echo cancellation to hearing aids.[8]
Sub-band Feedback Cancellation[edit]
Sub-band feedback cancellation is a type of adaptive feedback cancellation that relies less on computations and algorithms, but rather uses the signals already in the device to optimize the feedback cancellation. Sub-band feedback cancellations purpose is to make adaptive feedback cancellation cheaper and more widespread. [9]
Digital Signal Processing[edit]
Digital Signal Processing pledges to reduce the effect of adaptive feedback cancellation on sound quality with the use of feedback tests. The method also reports more gain in the hearing aid, and cites a figure of 10 decibels.[3]
Adaptive Feedback Cancellation in Smartphones[edit]
Research from 2018 is ongoing into adaptive feedback cancellation on smartphone speakers and microphones. Current research intends to use digital signal processing to mimic the cancellation in hearing aids in smartphones. [10]
References[edit]
- ^ "Feedback suppression". hearcom.eu. Retrieved 2020-10-27.
- ^ Proc. Mtgs. Acoust. 33, 055003 (2018); doi: 10.1121/2.0000836
- ^ a b Staff, Hearing Review. "Understanding Feedback and Digital Feedback Cancellation Strategies - Hearing Review". Retrieved 2020-10-27.
- ^ Levitt, Harry (2007). "A Historical Perspective on Digital Hearing Aids: How Digital Technology Has Changed Modern Hearing Aids". Trends in Amplification. 11 (1): 7–24. doi:10.1177/1084713806298000. ISSN 1084-7138. PMC 4111501. PMID 17301334.
- ^ Kates, James M. (2003), Benesty, Jacob; Huang, Yiteng (eds.), "Adaptive Feedback Cancellation in Hearing Aids", Adaptive Signal Processing: Applications to Real-World Problems, Signals and Communication Technology, Berlin, Heidelberg: Springer, pp. 23–57, doi:10.1007/978-3-662-11028-7_2, ISBN 978-3-662-11028-7, retrieved 2020-10-27
- ^ "Echo Cancellation - an overview | ScienceDirect Topics". www.sciencedirect.com. Retrieved 2020-10-27.
- ^ Avalos, J. Gerardo; Sanchez, Juan C.; Velazquez, Jose (2011-07-05). "Applications of Adaptive Filtering". Adaptive Filtering Applications. doi:10.5772/16873.
- ^ van Waterschoot, Toon; Moonen, Marc (2009-11-01). "Adaptive feedback cancellation for audio applications". Signal Processing. 89 (11): 2185–2201. doi:10.1016/j.sigpro.2009.04.036. ISSN 0165-1684.
- ^ Strasser, Falco; Puder, Henning (2015-12-01). "Adaptive feedback cancellation for realistic hearing aid applications". IEEE/ACM Transactions on Audio, Speech and Language Processing. 23 (12): 2322–2333. doi:10.1109/TASLP.2015.2479038. ISSN 2329-9290.
- ^ Proc. Mtgs. Acoust. 33, 055003 (2018); doi: 10.1121/2.0000836