Audio test mode

1. An audio system, comprising:

an input for receiving an input signal;

an output;

a sparsity detector for determining whether the input signal has a sparse representation in the frequency domain;

a switch, wherein the switch is controlled by an output signal from the sparsity detector based on a determination whether the input signal has a sparse representation in the frequency domain; and

a filter for filtering the input signal in at least one band pass filter,

wherein, if the input signal is determined to have a sparse representation in the frequency domain, the switch is controlled such that the output of the filter is passed to the output and therefore only components at at least one frequency of interest are passed to the output, and if the input signal is determined not to have a sparse representation in the frequency domain, the switch is controlled such that the input signal is passed to the output.

2. An audio system as claimed in claim 1 , configured for analysing the input signal to determine whether the input signal has a sparse representation in the frequency domain.

3. An audio system as claimed in claim 2 , configured for determining whether the input signal has a sparse representation in the frequency domain by passing the input signal to a Linear Predictive Coding block.

4. An audio system as claimed in claim 3 , configured for determining that the input signal has a sparse representation in the frequency domain if the Linear Predictive Coding block is able to identify one or more frequency component of the input signal, and subtracting the identified one or more frequency component from the input signal produces a result that is below a threshold.

5. An audio system as claimed in claim 2 , configured for determining whether the input signal has a sparse representation in the frequency domain by:

passing the input signal to a Fast Fourier Transform block; and

determining a number of significant frequency components in an output of the Fast Fourier Transform block.

6. An audio system as claimed in claim 5 , further configured for:

if it is determined that the input signal has a sparse representation in the frequency domain, passing the output signal of the Fast Fourier Transform block to an Inverse Sparse Fourier Transform block to generate an output signal in the time domain comprising only the significant frequency components.

7. An audio system as claimed in claim 2 , configured for determining whether the input signal has a sparse representation in the frequency domain by:

passing the input signal to a series of one or more notch filters, each having a respective notch filter frequency;

determining if an output of any notch filter is below a threshold; and

determining that the input signal has a sparse representation in the frequency domain if an output of one notch filter is below a threshold.

8. An audio system as claimed in claim 7 , further configured for, if it is determined that the input signal has a sparse representation in the frequency domain:

setting a pass band frequency of said at least one band pass filter to be equal to a respective notch filter frequency of a notch filter.

9. An audio system as claimed in claim 1 , configured for:

analysing the input signal to determine how many significant frequency components are present in the input signal.

10. An audio system as claimed in claim 9 , comprising at least one band pass filter, and configured for:

adapting the band pass filter to set a number of pass band frequencies thereof based on the determined number of significant frequency components present in the input signal.

11. A device comprising a system as claimed in claim 1 , wherein the device comprises a mobile telephone, an audio player, a video player, a mobile computing platform, a games device, a remote controller device, a toy, a machine, or a home automation controller or a domestic appliance.

12. A method of operation of an audio system, comprising:

receiving an input signal;

determining by means of a processing element whether the input signal has a sparse representation in the frequency domain, comprising components at at least one frequency of interest;

if the input signal is determined to have a sparse representation in the frequency domain, filtering the input signal in at least one band pass filter, such that only components at the or each frequency of interest are passed to an output; and

if the input signal is determined not to have a sparse representation in the frequency domain, passing the input signal to the output.

13. A method as claimed in claim 12 , comprising:

analysing the input signal to determine whether the input signal has a sparse representation in the frequency domain.

14. A method as claimed in claim 12 , comprising:

analysing the input signal to determine how many significant frequency components are present in the input signal.

15. A method as claimed in claim 14 , comprising:

adapting a band pass filter to set a number of pass band frequencies thereof based on the determined number of significant frequency components present in the input signal.

16. A method as claimed in claim 12 , comprising determining whether the input signal has a sparse representation in the frequency domain by passing the input signal to a Linear Predictive Coding block, and further comprising:

determining that the input signal has a sparse representation in the frequency domain if the Linear Predictive Coding block is able to identify one or more frequency component of the input signal, and subtracting the identified one or more frequency component from the input signal produces a result that is below a threshold.

17. A method as claimed in claim 12 , comprising determining whether the input signal has a sparse representation in the frequency domain by:

passing the input signal to a Fast Fourier Transform block; and

determining a number of significant frequency components in an output of the Fast Fourier Transform block, and further comprising:

if it is determined that the input signal has a sparse representation in the frequency domain, passing the output signal of the Fast Fourier Transform block to an Inverse Sparse Fourier Transform block to generate an output signal in the time domain comprising only the significant frequency components.

18. A method as claimed in claim 12 , comprising determining whether the input signal has a sparse representation in the frequency domain by:

passing the input signal to a series of one or more notch filters, each having a respective notch filter frequency;

determining if an output of any notch filter is below a threshold; and

determining that the input signal has a sparse representation in the frequency domain if an output of one notch filter is below a threshold, and further comprising, if it is determined that the input signal has a sparse representation in the frequency domain:

setting a pass band frequency of said at least one band pass filter to be equal to a respective notch filter frequency of a notch filter.

19. A method as claimed in claim 12 , wherein the input signal is considered to have a sparse representation in the frequency domain if the signal contains fewer than five frequency components at significant levels.

20. A non-transitory computer readable storage medium having computer-executable instructions stored thereon that, when executed by processor circuitry, cause the processor circuitry to perform a method according to claim 12 .