Telecoil Hum Filter Using Comb Notch Filtering
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Solution Overview
Problem
Telecoils in hearing aids and cochlear implants are sensitive to stray magnetic hum fields, particularly odd harmonics, which interfere with the desired audio signals and remain unresolved by existing filtering methods that either fail to eliminate hum or introduce audible artifacts.
Innovation Solution
A system and method employing a comb notch filter with a delay module and low-pass filtering to generate sharp nulls at specific harmonic frequencies, automatically detecting and applying the appropriate notch frequency (50 Hz or 60 Hz), and dynamically inserting or removing hum filtering based on need, thereby minimizing audible artifacts and enhancing listening experience.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If traditional filtering methods are used to reduce hum, then some hum attenuation is achieved, but audible artifacts are introduced and hum is not fully eliminated
Solution Approach 1:
The patent changes the parameter of filter design from traditional broad filtering to comb filtering with sharp notches at specific harmonic frequencies. By adjusting the notch frequencies to precisely match power frequencies (50/60 Hz) and their odd harmonics, the filter achieves targeted hum attenuation without broad frequency suppression that causes audible artifacts.
Solution Approach 2:
The comb notch filter applies filtering selectively only at specific harmonic frequencies where hum occurs, rather than applying broad filtering across the entire frequency spectrum. This localized filtering approach attenuates hum at problem frequencies while preserving the quality of desired audio signals in other frequency regions.
2Power
If telecoil sensitivity is increased to improve signal pickup, then desired audio signal strength is improved, but sensitivity to stray magnetic hum fields is also increased
Solution Approach 1:
The patent converts the harmful effect of telecoil sensitivity by using the same sensitive pickup capability to capture both desired signals and hum, then applying comb filtering to selectively remove hum components. The high sensitivity that originally caused hum pickup is now beneficial because it captures strong signals that can be processed and cleaned through frequency-selective filtering.
3Object-affected harmful factors
If filtering is applied to remove hum, then hum is reduced, but desired audio signal quality may be degraded
Solution Approach 1:
The patent changes the filtering approach from traditional broad-band filtering to narrow-band comb filtering with sharp notches. By precisely controlling the center frequencies and bandwidths of the notches to match only the hum frequencies (power frequencies and odd harmonics), the filter eliminates hum while preserving the quality of desired audio signals that fall outside these narrow notched frequencies.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively eliminates hum corresponding with power frequencies and their harmonics, reducing audible artifacts and improving the listening experience by generating sharp nulls at specific harmonic frequencies while maintaining the desired audio signal quality.
Implementation Method 1
Telecoils, also known as t-coils, are coils of wire wrapped around a core that induce an electric current when in the presence of a changing magnetic field
Data Source
AI summary
A system and/or method is provided for enhanced listening of audio signals acquired via a telecoil by performing hum filtering. The system may include a telecoil and a telecoil hum filter. The telecoil hum filter may include a comb notch filter. The comb notch filter may include a delay module and a comb notch filter summing module. The telecoil may be operable to receive a magnetic signal and convert the magnetic signal to an input audio signal. The delay module of the comb notch filter may be configured to generate a delayed signal by applying a delay to the input audio signal. The delay may be based on a fundamental hum frequency. The comb notch filter summing module may be configured to generate a comb notch filter output signal by adding the input audio signal and the delay signal.