Granted Patent B2

US 8,577,047 · App. 13/012,598 · Granted Nov 5, 2013

Abstract

Claims (33)

1. A loudspeaker drive circuit comprising:

a signal path compressor/limiter configured to change a peak-mean amplitude ratio in a time domain;

a feedforward control loop, comprising:

a control loop compressor/limiter corresponding to the signal path compressor/limiter;

a unit for computing a quality measure of the signal at an output of one of the control loop compressor/limiter and the signal path compressor/limiter based on an input signal of the feedforward control loop;

an excursion prediction unit for estimating a loudspeaker excursion based on the signal at the output of the control loop compressor/limiter; and

a controller for controlling the signal path compressor/limiter based on the quality measurement and excursion estimation.

2. A circuit as claimed in claim 1 , wherein the signal path compressor/limiter is adapted to apply a variable gain and implement a controllable dynamic range limiting function.

3. A circuit as claimed in claim 1 , wherein the signal path compressor/limiter comprises a variable gain unit and an amplitude clipping unit.

4. A circuit as claimed in claim 1 , further comprising an input filter.

5. A circuit as claimed in claim 4 wherein the input filter implements at least one of:

removing frequency components corresponding to at least one resonance peak in the acoustic output of the loudspeaker;

high pass filtering; boosting lower frequencies; and correcting the expected low efficiency with which low frequencies are reproduced by the loudspeaker.

6. A circuit as claimed in claim 4 , wherein the input filter is controlled by the controller.

7. A circuit as claimed in claim 1 , wherein the unit for computing a quality measure comprises means for comparing the signal before the control loop or signal path compressor/limiter with the signal after the control loop or signal path compressor/limiter.

8. A circuit as claimed in claim 1 , wherein the unit for computing comprises a module to model the non-linear effects that are present in the signal path.

9. A loudspeaker system comprising a circuit as claimed claim 1 and a loudspeaker.

10. A portable device comprising a loudspeaker system as claimed in claim 9 .

11. The portable device of claim 10 , wherein the portable device is a mobile telephone.

12. A method of processing an audio input signal to derive a loudspeaker drive signal, comprising:

using a signal path compressor/limiter to change a peak-mean amplitude ratio of an audio input signal in a time domain;

within a feedforward control loop:

using a control loop compressor/limiter corresponding to the signal path compressor/limiter;

computing a quality measure of the signal at an output of one of the control loop compressor/limiter and the signal path compressor/limiter based on an input signal of the feedforward control loop;

estimating a loudspeaker excursion based on the signal at the output of the control loop compressor/limiter; and

controlling the signal path compressor/limiter based on the quality measurement and excursion estimation.

13. A method as claimed in claim 12 , wherein using the signal path compressor/limiter comprises applying a variable gain and implementing a controllable dynamic range limiting function.

14. A method as claimed in claim 12 , further comprising filtering the audio input signal before application to the signal path compressor/limiter to:

remove frequency components corresponding to at least one resonance peak in the acoustic output of the loudspeaker, and/or

perform high pass filtering, and/or

boost lower frequencies, and/or

correct the expected low efficiency with which low frequencies are reproduced by the loudspeaker.

15. A method as claimed in claim 14 , wherein the filtering is controlled by the feedforward control loop.

Assignments (11)