Apparatus, systems and methods for inaudibly identifying an audio accessory using spectral shaping

1. A method for identifying an audio accessory coupled to an electronic device, comprising:

applying at least one detection pulse to the accessory over an audio jack, each detection pulse excluding at least one of:

energies that are above a lower audible human threshold, and

frequency components within the human audible frequency range so as to be inaudible to a human;

receiving at the electronic device at least one response signal from the audio accessory, each response signal corresponding to a detection pulse;

wherein each detection pulse is sufficiently long such that the at least one response signal will settle to a stable current;

measuring the at least one response signal after it has settled to determine an impedance of the audio accessory; and

based on the determined impedance, identifying the audio accessory as a particular audio accessory.

2. A method for identifying an audio accessory coupled to an electronic device, comprising:

applying at least one detection pulse to the audio accessory, each detection pulse being spectrally shaped to be inaudible to a human user;

receiving at least one response signal corresponding to each detection pulse that is indicative of the impedance of the accessory; and

based on the impedance, identifying the accessory.

3. The method of claim 2 , wherein the shaped detection pulse includes a low frequency detection pulse.

4. The method of claim 3 , wherein the low frequency detection pulse has an energy content that is below an audible frequency range.

5. The method of claim 2 , wherein the shaped detection pulse excludes energies above a lower audible human threshold.

6. The method of claim 5 , wherein the shaped detection pulse includes a portion within the human audible frequency range.

7. The method of claim 2 , wherein the shaped detection pulse includes a high-frequency detection pulse.

8. The method of claim 7 , wherein the high-frequency detection pulse has an energy content that is above an audible frequency range.

9. The method of claim 7 , wherein the shape of the detection pulse is stored in hardware.

10. The method of claim 7 , wherein the detection pulse is shaped using a highpass filter located between a pulse generator on the electronic device and the audio accessory.

11. The method of claim 10 , wherein the highpass filter has a cutoff frequency above 20 kHz.

12. The method of claim 10 , wherein at least a portion of the shaped detection pulse leaks though the highpass filter into the audible frequency range.

13. The method of claim 12 , wherein the leaked portion is shaped to be below the lower audible human threshold.

14. The method of claim 2 , further comprising applying matched filtering to the response signal to reduce the influence of noise.

15. The method of claim 2 , wherein the at least one shaped detection pulse includes a plurality of shaped detection pulses.

16. The method of claim 15 , wherein the plurality of shaped detection pulses generate a plurality of response signals, and the plurality of response signals are averaged to determine the impedance.

17. The method of claim 15 , wherein at least one of the shaped detection pulses has inverted amplitude and is subtracted from another shaped detection pulse to reduce the influence of noise.

18. The method of claim 2 , wherein the response signal is settled before the impedance is measured.

19. The method of claim 2 , wherein the shaped detection pulse excludes energies that are above the lower audible human threshold, and frequency components within the human audible frequency range.

20. An electronic device for identifying an audio accessory coupled thereto, comprising:

a pulse generator that generates at least one detection pulse and applied the detection pulse to an audio accessory over an audio jack, each detection pulse being spectrally shaped to be generally inaudible to a human user; and

a detector for receiving at least one response signal corresponding, each response signal corresponding to one of the at least one detections pulse and being indicative of the impedance of the audio accessory, wherein

the audio accessory is identified as a particular audio accessory based on the impedance detected by said detector.