Index scheming for filter parameters

1. A method comprising:

deriving magnitude response information of a prototype filter from a first filter, the derived magnitude response information including a plurality of prototype gain values, at least one of the plurality of prototype gain values including a first prototype gain corresponding to a first frequency, wherein the first prototype gain differs from a first gain of the first filter corresponding to the first frequency;

storing the magnitude response information of the prototype filter;

retrieving the magnitude response information of the prototype filter at the first frequency;

computing gains for a plurality of control frequencies based on the magnitude response information of the prototype filter.

2. The method of claim 1 , wherein deriving the magnitude response information of the prototype filter includes:

determining a magnitude response information of a high-shelving equalizer,

scaling the magnitude response information of the high-shelving equalizer, and

shifting the scaled magnitude response information of the high-shelving equalizer along a frequency axis by a predetermined frequency amount, wherein the shifted scaled magnitude response is the magnitude response information of the first filter.

3. The method of claim 2 , wherein the predetermined frequency amount is equal to an amount needed to match the scaled magnitude response information of the high-shelving equalizer to the magnitude response information of the prototype filter.

4. The method of claim 1 , wherein the deriving the magnitude response information of the prototype filter includes:

determining a magnitude response information of a low-shelving equalizer,

scaling the magnitude response information of the low-shelving equalizer, and

shifting the scaled magnitude response information of the low-shelving equalizer along a frequency axis by a predetermined frequency amount, wherein the shifted scaled magnitude response is the magnitude response information of the prototype filter.

5. The method of claim 1 , wherein the determination of the magnitude response information of the prototype filter includes flipping a magnitude response of a low-shelving equalizer along a frequency axis.

6. The method of claim 1 , wherein the determination of the magnitude response information of the prototype filter includes flipping a magnitude response of a high-shelving equalizer along a frequency axis.

7. The method of claim 1 , wherein the storage of the magnitude response information of the prototype filter includes storing the magnitude response information of the prototype filter in a lookup table.

8. The method of claim 7 , wherein the lookup table includes equally spaced entries of the magnitude response information of the prototype filter.

9. The method of claim 7 , wherein the first frequency is proximate to DC or Nyquist, wherein the retrieval of the magnitude response information of the prototype filter at the first frequency includes setting the magnitude response information to be equal to a saturation value.

10. The method of claim 1 , further comprising:

determining one or more properties of an environment; and

determining one or more parameters based on the determined one or more properties of the environment,

wherein the determined one or more parameters are used for the retrieval of the magnitude response information of the prototype filter at the first frequency.

11. The method of claim 10 , wherein the determination of the one or more properties of environment includes:

generating a test audio signal;

determining a response to the generated test audio signal; and

determining the one or more properties of the environment based on changes between the test audio signal and the response.

12. The method of claim 1 , further comprising:

determining one or more actions of a user of a wearable head device; and

determining one or more parameters, wherein the retrieval of the magnitude response information of the prototype filter at the first frequency is based on the determined one or more actions,

wherein the determined one or more parameters are used for the retrieval of the magnitude response information of the prototype filter at the first frequency.

13. The method of claim 1 , wherein the retrieval of the magnitude response information of the prototype filter includes:

determining an index associated with the first frequency, and

using the determined index to find a corresponding index in a lookup table for the retrieval of the magnitude response information.

14. The method of claim 1 , further comprising applying the computed gains to the audio signal.

15. A system comprising:

a wearable head device configured to provide an audio signal to a user; and

circuitry configured to:

derive magnitude response information of a prototype filter from a first filter, the derived magnitude response information including a plurality of prototype gain values, at least one of the plurality of prototype gain values including a first prototype gain corresponding to a first frequency, wherein the first prototype gain differs from a first gain of the first filter corresponding to the first frequency;

store the magnitude response information of the prototype filter;

retrieve the magnitude response information of the prototype filter at the first frequency;

compute gains for a plurality of control frequencies based on the magnitude response information of the prototype filter.

16. The system of claim 14 , further comprising:

memory that stores the magnitude response information of the prototype filter.

17. The system of claim 15 , wherein the magnitude response information of the prototype filter is stored in a lookup table that includes equally spaced entries of the magnitude response information of the prototype filter.

18. The system of claim 15 , wherein the magnitude response information of the prototype filter is stored in a lookup table, wherein the lookup table includes a plurality of indices, each index associated with a plurality of frequencies.

19. The system of claim 14 , wherein the wearable head device comprises one or more sensors,

wherein the system is configured to determine one or more properties of an environment,

wherein the circuitry is further configured to determine one or more parameters based on the determined one or more properties of the environment, and

wherein the retrieval of the magnitude response information of the prototype filter at the first frequency is based on the determined one or more parameters.

20. The system of claim 18 , wherein the wearable head device comprises:

one or more speakers configured to generate a test audio signal, and

one or more sensors configured to determine a response to the generated test audio signal,

wherein the one or more properties of the environment is determined by the circuitry based on changes between the test audio signal and the response.