Audio driver system and method
View Patent ↗A system and apparatus for constructing a displacement model across a frequency range for a loudspeaker is disclosed. The resultant displacement model is centered around the distortion point. Once a distortion model is constructed it can be incorporated into an audio driver to prevent distortion by incorporating the model and a distortion compensation unit with a conventional audio driver. Various topologies can be used to incorporate a distortion model and distortion compensation unit into an audio driver. Furthermore, a wide variety of distortion compensation techniques can be employed to avoid distortion in such an audio driver.
1. A method for use in an audio system, the method comprising:
(a) selecting a frequency in a frequency range;
(b) selecting an amplitude from a plurality of amplitudes;
(c) causing a signal generator to generate a signal at the frequency and the amplitude;
(d) providing the signal to a loudspeaker to generate a sound;
(e) generating a sound signal representing the sound using a microphone;
(f) determining whether the sound signal has a distortion;
(g) if the determining determines that the sound signal does not have the distortion and if a last amplitude of the plurality of amplitudes has not been reached, selecting another amplitude of the plurality of amplitudes and repeating steps (c)-(g) until the determining determines that the sound signal has the distortion;
(h) recording, in response to determining that the sound signal has the distortion, the another amplitude causing the distortion as a minimum amplitude; and
(i) filtering an audio signal utilizing the minimum amplitude.
2. The method of claim 1 , wherein the determining whether the sound signal has a distortion comprises:
predicting an expected microphone signal based on the signals generated by the signal generator; and
comparing the expected microphone signal with the sound signal representing the sound using the microphone.
3. The method of claim 2 , wherein the expected microphone signal is predicted using a linear predictive filter.
4. The method of claim 1 , wherein filtering the audio signal further utilizes recorded phases along with the minimum amplitude to create complex samples from the minimum amplitude and the recorded phases.
5. The method of claim 4 further comprising:
constructing a transfer function by fitting the complex samples to an infinite impulse response (IIR) filter; and
inverting the transfer function to create an inverse transfer function.
6. An audio driver comprising:
a digital to analog converter (DAC);
an amplifier;
a signal generator; and
an analysis module configured to:
(a) select a frequency in a frequency range;
(b) select an amplitude from a plurality of amplitudes;
(c) cause the signal generator to generate a signal having the frequency and the amplitude;
(d) determine whether the signal has the distortion;
(e) if the determining determines that the signal does not have the distortion and if a last amplitude of the plurality of amplitudes has not been reached, selecting another amplitude of the plurality of amplitudes and repeating steps (c)-(e);
(f) record, in response to determining that the signal has the distortion, the another amplitude causing the distortion as a minimum amplitude; and
(g) filter an audio signal utilizing the minimum amplitude.
7. The audio driver of claim 6 further comprising:
a distortion compensation unit for receiving the signal; and
a distortion model configured to determine if distortion exists in the distortion compensation unit.
8. The audio driver of claim 7 wherein the distortion model is coupled to an audio input or an audio signal output of the distortion compensation unit.
9. The audio driver of claim 7 wherein the distortion model utilizes speaker displacement to predict the distortion.
10. The audio driver of claim 9 further comprising a distortion detection unit coupled to a microphone, wherein the distortion detection unit generates revision data for the distortion model if the signal is determined to have the distortion.
11. The audio driver of claim 7 further comprising:
a resistor in series with a loudspeaker;
a differential amplifier operable to measure a voltage across the resistor; and
a distortion detection unit operable to receive the measured voltage, wherein the distortion detection unit causes a revision in the distortion model if the signal is determined to have the distortion.
12. The audio driver of claim 7 further comprising a distortion detection unit operable to receive a signal proportional to a loudspeaker current, wherein the distortion detection unit causes a revision in the distortion model if the signal is determined to have the distortion.
13. The audio driver of claim 7 wherein the distortion compensation unit comprises a dynamic range compressor.
14. The audio driver of claim 7 wherein the distortion compensation unit comprises a gain element with an automatic gain control.
15. The audio driver of claim 7 wherein the distortion compensation unit comprises a look ahead peak reducer.
16. The audio driver of claim 7 , wherein the distortion compensation unit comprises an adder operable to add a DC offset or a low frequency signal.
17. The audio driver of claim 7 wherein the distortion compensation unit comprises a PID controller.
18. The audio driver of claim 7 wherein the distortion compensation unit comprises a gain element with automatic gain control and an adder operable to add an offset or a low frequency signal.
19. The audio driver of claim 18 wherein the distortion compensation unit further comprises a PID control operable to control the adder and the gain element.