Audio headset with active noise control of the non-adaptive type for listening to an audio music source and/or for “hands-free” telephony functions
The headset comprises two earpieces each having a transducer for playing back the sound of an audio signal and received in an acoustic cavity defined by a shell having an ear-surrounding cushion. The active noise control comprises, in parallel, a feedforward bandpass filter receiving the signal from an external microphone, a feedback bandpass filter receiving as input an error signal delivered by an internal microphone, and a stabilizer bandpass filter locally increasing the phase of the transfer function of the feedback filter in an instability zone, in particular a waterbed effect zone around 1 kHz. A summing circuit delivers a weighting linear combination of the signal delivered by these filters together with the audio signal to be played back. Control is non-adaptive, with the parameters of the filters being static.
1. An audio headset comprising two earpieces connected together by a headband and each including a transducer for playing back the sound of an audio signal that is to be reproduced, the transducer being housed in an acoustic cavity defined by a shell provided with an ear-surrounding cushion, the headset including an active noise control system comprising:
an open-loop feedforward first branch with a first bandpass filter receiving as input a signal delivered by an external microphone suitable for picking up acoustic noise existing in the environment of the headset;
a closed-loop feedback second branch with a second bandpass filter receiving as input an error signal delivered by an internal microphone inside the cavity;
a third branch with a third filter; and
a mixer circuit receiving as inputs the signals delivered by the first, second, and third filters and also the audio signal to be played back, and delivering as output a signal suitable, after amplification, for controlling the transducer;
wherein:
the active noise control is non-adaptive control, the parameters of the first, second, and third filters being predetermined parameters;
the third filter is a stabilizer bandpass filter connected in parallel with the feedback second branch, receiving as input the signal delivered by the internal microphone, and delivering as output a signal that is applied as an input to the mixer circuit, the third filter being suitable for locally increasing the phase of the transfer function of the second filter in a predetermined instability zone; and
the first, second, and third branches are arranged in parallel, and the mixer circuit is a summing circuit delivering as output a linear combination of the signals delivered by the first, second, and third filters together with at least a fraction of the audio signal to be played back, with respective weighting of the gains applied to these signals.
2. The audio headset of claim 1 , wherein said predetermined instability zone is a waterbed effect zone around a frequency of 1 kHz.
3. The audio headset of claim 1 , wherein the high cutoff frequency of the second filter is less than 150 Hz.
4. The audio headset of claim 1 , wherein the bandwidth of the second filter is less than 65 Hz.
5. The audio headset of claim 1 , wherein the gain margin of the feedback branch of the active noise control is at least 15 dB.
6. The audio headset of claim 1 , wherein the phase margin of the feedback branch of the active noise control is at least 45°.
7. The audio headset of claim 1 , wherein the audio signal to be played back is applied as input both to the second filter and to the summing circuit, the second filter receiving as input a signal obtained by combining said error signal delivered by the internal microphone with at least a fraction of the audio signal for play-back.
8. The audio headset of claim 7 , wherein the audio signal that is to be played back is not applied to the third filter.