Telecoil hum filter
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.
1. A system comprising:
a telecoil operable to receive a magnetic signal and convert the magnetic signal to an input audio signal; and
a telecoil hum filter comprising:
a comb notch filter configured to provide attenuation notches at odd harmonic frequencies in the input audio signal below a cutoff frequency, the comb notch filter comprising:
a delay module and a low pass filter configured to generate a filtered delayed signal by filtering and applying a delay to the input audio signal, wherein the delay is equal to:
1
2
*
freq
where freq is the fundamental hum frequency, and
a comb notch filter summing module configured to generate a comb notch filter output signal by adding the input audio signal and the filtered delayed signal.
2. The system of claim 1 , wherein the low-pass filter comprises the cutoff frequency oft kHz.
3. The system of claim 1 , wherein the delay module and the low-pass filter form a digital finite impulse response filter.
4. The system of claim 3 , wherein the digital finite impulse response filter comprises:
a digital delay line having a plurality of delay elements configured to delay a sample of the input audio signal;
a plurality of filter taps, each of the plurality of filter taps configured to apply a filter coefficient to one of the input audio signal or an output of one of the plurality of delay elements, and
a finite impulse response filter summing module configured to add the outputs of the filter taps to generate the filtered delayed signal.
5. The system of claim 1 , comprising a processor configured to automatically determine and select the delay.
6. The system of claim 5 , wherein the processor is configured to:
periodically switch between an 8.33 msec delay and a 10 msec delay,
acquire results of the 8.33 msec delay and the 10 msec delay, and
compare the results to automatically determine and select the delay.
7. The system of claim 1 , comprising a processor configured to:
compare the input audio signal and the comb notch filter output signal; and
select one of the input audio signal or the comb notch filter output signal based on the comparison.
8. A method comprising:
receiving a magnetic signal at a telecoil;
converting the magnetic signal to an input audio signal at the telecoil;
generating a filtered delayed signal at a low-pass filter and a delay module of a comb notch filter by providing attenuation notches at odd harmonic frequencies in the input audio signal below a cutoff frequency, wherein the filtered delayed signal is generated by filtering and applying a delay to the input audio signal, wherein the delay is equal to:
1
2
*
freq
where freq is the fundamental hum frequency, and
generating a comb notch filter output signal at a comb notch filter summing module by adding the input audio signal and the filtered delayed signal.
9. The method of claim 8 , wherein the filtering and applying the delay to the input audio signal comprises:
delaying a sample of the input audio signal by each of a plurality of delay elements of a digital delay line;
applying a filter coefficient by each of a plurality of filter taps, wherein the filter coefficient is applied to one of the input audio signal or an output of one of the plurality of delay elements; and
adding, by a finite impulse response filter summing module, the outputs of the filter taps to generate the filtered delayed signal.
10. The method of claim 8 , comprising selectively providing a bass boost to the comb notch filter output signal.
11. The method of claim 8 , comprising:
comparing the input audio signal and the comb notch filter output signal; and
selecting one of the input audio signal or the comb notch filter output signal based on the comparison.
12. The method of claim 8 , wherein the low-pass filter comprises the cutoff frequency of 1 kHz.
13. The method of claim 8 , wherein the delay module and the low-pass filter form a digital finite impulse response filter.
14. The method of claim 8 , comprising automatically determining and selecting the delay.
15. The method of claim 14 , comprising:
periodically switching between an 8.33 msec delay and a 10 msec delay,
acquiring results of the 8.33 msec delay and the 10 msec delay, and
comparing the results to automatically determine and select the delay.
16. A non-transitory computer readable medium having stored thereon, a computer program having at least one code section, the at least one code section being executable by a machine for causing the machine to perform steps comprising:
receiving an input audio signal from a telecoil;
generating a filtered delayed signal at a low-pass filter and a delay module of a comb notch filter by providing attenuation notches at odd harmonic frequencies in the input audio signal below a cutoff frequency, wherein the filtered delayed signal is generated by filtering and applying a delay to the input audio signal, wherein the delay is equal to:
1
2
*
freq
where freq is the fundamental hum frequency; and
generating a comb notch filter output signal at a comb notch filter summing module by adding the input audio signal and the filtered delayed signal.
17. The non-transitory computer readable medium of claim 16 , wherein the filtering and applying the delay to the input audio signal comprises:
delaying a sample of the input audio signal by each of a plurality of delay, elements of a digital delay line;
applying a filter coefficient by each of a plurality of filter taps, wherein the filter coefficient is applied to one of the input audio signal or an output of one of the plurality of delay elements; and
adding, by a finite impulse response filter summing module, the outputs of the filter taps to generate the filtered delayed signal.
18. The non-transitory computer readable medium of claim 16 , comprising selectively providing a bass boost to the comb notch filter output signal.
19. The non-transitory computer readable medium of claim 16 , comprising:
comparing the input audio signal and the comb notch filter output signal; and
selecting one of the input audio signal or the comb notch filter output signal based on the comparison.
20. The non-transitory computer readable medium of claim 16 , wherein the low-pass filter comprises the cutoff frequency of 1 kHz.
21. The non-transitory computer readable medium of claim 16 , wherein the delay module and the low-pass filter form a digital finite impulse response filter.
22. The non-transitory computer readable medium of claim 16 , comprising automatically determining and selecting the delay.
23. The non-transitory computer readable medium of claim 22 , comprising:
periodically switching between an 8.33 msec delay and a 10 msec delay,
acquiring results of the 8.33 msec delay and the 10 msec delay, and
comparing the results to automatically determine and select the delay.