System and method for use in haptic signal generation

1. A processing system for a haptic signal generation system, the processing system comprising:

an input for receiving an input signal derived from an audio signal;

a threshold setting mechanism configured, based on a first representation derived from the input signal, to adaptively adjust an existing threshold to derive a first threshold if a correspondence between the existing threshold and the first representation is not met, wherein the first representation comprises a time-varying peak estimate of a time-varying property of the input signal and wherein the existing threshold and first threshold are threshold values of that property; and

a gain determining mechanism configured to determine an output gain to be applied to a haptic signal based on a comparison between the first threshold and a second representation derived from the input signal, wherein the second representation comprises an envelope of the time-varying property of the input signal;

wherein the gain determining mechanism is configured to determine a ratio between the first threshold and the second representation; and

wherein the ratio is processed such that when the first threshold and the second representation are equal, the output gain is substantially zero.

2. A processing system as claimed in claim 1 , wherein the threshold setting mechanism is configured to:

i) adjust the first threshold upwards if the first representation exceeds the first threshold by a predetermined amount;

ii) adjust the first threshold downwards if the first representation is below the first threshold by a predetermined amount.

3. A processing system as claimed in claim 1 wherein the first representation comprises a representation of peak power levels of the audio signal.

4. A processing system as claimed in claim 1 , wherein the second representation comprises a power envelope of the audio signal.

5. A processing system as claimed in claim 4 wherein the power envelope comprises a smoothed power envelope that rises more quickly when a power level of the input signal rises and falls relatively slowly when the power level of the input signal falls.

6. A processing system as claimed in claim 1 , further comprising a saturation mechanism configured to saturate the range of the output gain between zero and 1.

7. A haptic signal generation system comprising a processing system as claimed in claim 1 , further comprising:

an audio signal input for receiving an audio signal; and

a haptic signal generator for generating a haptic signal,

wherein the output gain determined by the gain determining mechanism, or a value derived therefrom, is applied to the haptic signal, and wherein a haptic output signal is generated if the second representation exceeds the first threshold or comes within range of the first threshold.

8. A haptic signal generation system as claimed in claim 7 , the system further comprising a filtering mechanism provided in advance of the processing system and configured to exclude selected frequencies.

9. A haptic signal generation system as claimed in claim 8 , wherein the filtering mechanism comprises first and second filters each having a different cutoff frequency that is selected to remove first and second components of the audio signal.

10. A haptic signal generation system as claimed in claim 9 , wherein the first filter comprises a low pass filter and the second filter comprises a high pass filter.

11. A haptic signal generation system as claimed in claim 9 , further comprising a second threshold evaluation mechanism which is configured to receive first and second input signals derived from the output of the first and second filters.

12. A haptic signal generation system as claimed in claim 11 , wherein the second threshold evaluation mechanism is configured to determine a product of the first and second input signals and to issue a haptic trigger signal if the magnitude of the product is sufficiently high to indicate that both the magnitude of both the first and second input signals is high.

13. A haptic signal generation system as claimed in claim 7 , further comprising a re-set mechanism, the re-set mechanism being configured to restore the first threshold to an initial value if a condition of silence is met for a pre-set time period.

14. A haptic signal generation system as claimed in claim 13 , wherein a condition of silence is met if a metric derived from the at least one input signal to the processing system is the less than or equal to a third threshold.

15. A haptic signal generation system as claimed in claim 14 , wherein a condition of silence is met if the first input signal is less than or equal to a third threshold.

16. A haptic signal generation system as claimed in claim 14 wherein the re-set mechanism is configured to advance a counter value if the condition of silence is met, wherein if the counter value exceeds a pre-set time period, the processing system is configured to restore the first threshold to the initial value.

17. A method of generating an output gain to be applied to a haptic signal, the method comprising:

receiving an input signal derived from an audio signal;

deriving a first representation from the input signal;

adjusting an existing threshold to derive a first threshold if a correspondence between the existing threshold and the first representation is not met, wherein the first representation comprises a time-varying peak estimate of a time-varying property of the input signal and wherein the existing threshold and first threshold are threshold values of that property; and

comparing the first threshold and a second representation derived from the input signal in order to generate the output gain, wherein the second representation comprises an envelope of the time-varying property of the input signal;

wherein the method comprises determining a ratio between the first threshold and the second representation, and processing the ratio such that when the first threshold and the second representation are equal, the output gain is substantially zero.

18. A method according to claim 17 , further comprising:

applying the output gain, or a value derived therefrom, to a haptic signal; and

generating a haptic output signal if the second representation exceeds the first threshold or comes within range of the first threshold.

19. A haptic signal generation system comprising a processing system, the processing system comprising:

an input for receiving an input signal derived from an audio signal;

a threshold setting mechanism configured, based on a first representation derived from the input signal, to adaptively adjust an existing threshold to derive a first threshold if a correspondence between the existing threshold and the first representation is not met, wherein the first representation comprises a time-varying peak estimate of a time-varying property of the input signal and wherein the existing threshold and first threshold are threshold values of that property; and

a gain determining mechanism configured to determine an output gain to be applied to a haptic signal based on a comparison between the first threshold and a second representation derived from the input signal, wherein the second representation comprises an envelope of the time-varying property of the input signal,

wherein the haptic signal generation system further comprises:

an audio signal input for receiving the audio signal;

a filtering mechanism provided in advance of the processing system and configured to exclude selected frequencies, the filtering mechanism comprising first and second filters each having a different cutoff frequency that is selected to remove first and second components of the audio signal;

a second threshold evaluation mechanism which is configured to receive first and second input signals derived from the output of the first and second filters; and

a haptic signal generator for generating the haptic signal,

wherein the output gain determined by the gain determining mechanism, or a value derived therefrom, is applied to the haptic signal, and wherein a haptic output signal is generated if the second representation exceeds the first threshold or comes within range of the first threshold.

20. A haptic signal generation system comprising a processing system, the processing system comprising:

an input for receiving an input signal derived from an audio signal;

a threshold setting mechanism configured, based on a first representation derived from the input signal, to adaptively adjust an existing threshold to derive a first threshold if a correspondence between the existing threshold and the first representation is not met, wherein the first representation comprises a time-varying peak estimate of a time-varying property of the input signal and wherein the existing threshold and first threshold are threshold values of that property; and

a gain determining mechanism configured to determine an output gain to be applied to a haptic signal based on a comparison between the first threshold and a second representation derived from the input signal, wherein the second representation comprises an envelope of the time-varying property of the input signal,

wherein the haptic signal generation system further comprises:

a re-set mechanism, the re-set mechanism being configured to restore the first threshold to an initial value if a condition of silence is met for a pre-set time period;

an audio signal input for receiving the audio signal;

a haptic signal generator for generating the haptic signal,

wherein the output gain determined by the gain determining mechanism, or a value derived therefrom, is applied to the haptic signal, and wherein a haptic output signal is generated if the second representation exceeds the first threshold or comes within range of the first threshold.