Headphone for active noise suppression
The disclosed active noise suppression headphone system is directed to a headphone system that is capable of substantially suppressing high or low frequency interfering noise that penetrate through a headphone earpiece from multiple directions. An external microphone mounted with a housing of a headphone earpiece senses ambient noise outside of the earpiece. The sensed ambient noise may be processed through at least one parallel filter bank arranged in at least one headphone earpiece. Each parallel filter bank may include adaptively linked filters. The output of these filters may be amplified based on weighting factors that are dependent upon the sensed ambient noise and that are generated by a filtered x least mean square circuit. The amplified filtered outputs may be summed to generate an antinoise signal that is in input to a loudspeaker within the headphone earpiece that substantial suppresses the ambient noise before it can be perceived by an end user of the headphones.
1. An active noise suppression headphone apparatus, comprising:
an earpiece having a housing;
an external microphone mounted with the housing, the external microphone configured to sense ambient noise outside of the housing;
a loudspeaker positioned within the housing; and
a parallel filter bank including at least two adaptively linked filters,
where an output of each of the at least two adaptively linked filters are coupled to an adder, and where an output of the adder is coupled to the loudspeaker, and
an adjustable amplifier bank that includes an adjustable amplifier for each of the at least two adaptively linked filters, and where a corresponding adjustable amplifier is serially positioned between the adaptively linked filters of the parallel filter bank and the adder, and further where each adjustable amplifier is weighted depending on a direction of incidence of the ambient noise sensed by the external microphone.
2. The active noise suppression headphone apparatus of claim 1 , where the at least two adaptively linked filters comprise analog filters.
3. The active noise suppression headphone apparatus of claim 1 , where the adjustable amplifier bank comprises voltage-controlled amplifiers.
4. The active noise suppression headphone apparatus of claim 1 , further comprising an error microphone positioned within the housing and downstream of an output of the loudspeaker, where the error microphone feeds an error signal to a fxLMS circuit that is coupled to the adjustable amplifier bank.
5. The active noise suppression headphone apparatus of claim 1 , further comprising:
a voltage-controlled amplifier bank that includes a plurality of adjustable amplifiers; and
an error microphone positioned within the housing and downstream of an output of the loudspeaker,
where each adjustable amplifier is weighted depending on the direction of incidence of the ambient noise sensed by the external microphone; and
where the error microphone is coupled to a fxLMS circuit that is coupled to the voltage-controlled amplifier bank.
6. A method for active noise suppression in a headphone, comprising:
sensing an ambient noise with an external microphone mounted with a headphone earpiece;
passing the sensed ambient noise through at least two adaptively linked analog filters;
amplifying each of the filtered ambient noise signals with corresponding voltage-controlled amplifiers that are weighted depending on a direction of incidence of the ambient noise sensed by the external microphone;
summing an output of the filtered signals to generate an antinoise signal; and
inputting the antinoise signal to a loudspeaker positioned within the headphone earpiece.
7. The method of claim 6 , where each corresponding voltage-controlled amplifier is controlled by an fxLMS algorithm based on an error feedback signals of an error microphone and the filtered ambient noise signals.
8. The method of claim 6 , where the weighting of each voltage-controlled amplifiers comprises a weighting factor (.mu.), an error signal (e) of an error microphone, and an intermediate signal obtained from the corresponding filtered ambient noise signals and a filter with an estimated value of a secondary path.
9. The method of claim 6 , where a residual noise spectrum resulting after noise suppression consists of a transfer function of the external microphone to an error microphone downstream of the loudspeaker, the transfer function represented by of a received interference signal spectrum (X), analog filters (H 1 . . . H n ) and the corresponding weightings (w 1 . . . w n ) to:
E
=
(
K
-
∑
i
=
1
n
w
1
H
1
)
X
where X represents a received interference signal spectrum,
H 1 . . . H n represents the adaptively linked analog filters, and
w 1 . . . w n represents the corresponding weight of the voltage-controlled amplifiers.
10. A method for active noise suppression in a headphone, comprising:
sensing an ambient noise with an external microphone counted with a headphone earpiece;
passing the sensed ambient noise through at least two adaptively linked analog filters;
summing an output of the filtered signals to generate an antinoise signal;
inputting the antinoise signal to a loudspeaker positioned within the headphone earpiece;
receiving an error signal from an error microphone positioned downstream of the loudspeaker in the headphone earpiece,
digitizing the sensed ambient noise and passing it through a digitally simulated secondary path and passing the output through a digital filter simulation of the at least two adaptively linked analog filters; and
driving a digital fxLMS circuit with the output of the digital filter simulation and a digitized error signal to generate weights that control voltage-controlled amplifiers that amplify the output of at least two adaptively linked analog filters before the summing act.
11. A method for active noise suppression in a headphone, comprising:
sensing an ambient noise with an external microphone counted with a headphone earpiece;
passing the sensed ambient noise through a first filter bank of at least two adaptively linked analog filters;
summing an output of the filtered signals to generate an antinoise signal;
inputting the antinoise signal to a loudspeaker positioned within the headphone earpiece;
receiving an error signal from an error microphone positioned downstream of the loudspeaker in the headphone earpiece,
passing the sensed ambient noise through a simulated secondary path and a second filter bank of at least two adaptively linked analog filters; and
driving a fxLMS circuit with the outputs of the second filter bank and an error signal to generate weights that control voltage-controlled amplifiers that amplify the output of the first filter bank of at least two adaptively linked analog filters before the summing act.
12. The method of claim 11 , where the at least two adaptively linked analog filters of the first filter bank comprise different interference transfer functions from the external microphone to the error microphone.
13. The method of claim 11 , where the at least two adaptively linked analog filters of the first filter bank comprise different secondary path compensations from the external microphone to the error microphone.