Systems and methods of adjusting bass levels of multi-channel audio signals

1. A playback device comprising:

a plurality of audio drivers;

one or more processors;

tangible, non-transitory, computer-readable media storing instructions executable by the one or more processors to cause the playback device to perform operations comprising:

receiving a multi-channel audio signal representing multi-channel audio content for playback via the playback device;

separating, from respective channels of the multi-channel audio signal, respective low-frequency audio signals comprising frequencies less than a threshold frequency;

determining respective electrical energies of each respective low-frequency audio signal;

determining a first energy by summing the respective electrical energies of each respective low-frequency audio signal;

consolidating the respective low-frequency audio signals into a consolidated low-frequency audio signal;

determining a second energy by determining an electrical energy of the consolidated low-frequency audio signal;

generating a gain-adjusted low-frequency audio signal by adjusting a gain of the consolidated low-frequency audio signal based on both (i) the first energy and (ii) the second energy;

generating a gain-adjusted multi-channel audio signal by mixing the gain-adjusted low-frequency audio signal back into the respective channels of the multi-channel audio signal; and

using the gain-adjusted multi-channel audio signal to play back gain-adjusted multi-channel audio content via the plurality of audio drivers.

2. The playback device of claim 1 , wherein the multi-channel audio signal comprises a left-channel audio signal, a center-channel audio signal, and a right-channel audio signal, and wherein separating, from the respective channels of the multi-channel audio signal, the respective low-frequency audio signals that are below the threshold frequency comprises:

separating, from the left-channel audio signal, a first low-frequency audio signal comprising first frequencies less than the threshold frequency;

separating, from the center-channel audio signal, a second low-frequency audio signal comprising second frequencies less than the threshold frequency; and

separating, from the right-channel audio signal, a third low-frequency audio signal comprising third frequencies less than the threshold frequency.

3. The playback device of claim 2 , wherein the first low-frequency audio signal is different than the second and third low-frequency audio signals, and wherein the second low-frequency audio signal is different than the third low-frequency audio signal.

4. The playback device of claim 1 , wherein the multi-channel audio signal comprises a plurality of frames of audio content, wherein determining the respective electrical energies of each respective low-frequency audio signal comprises determining, for an individual frame of the plurality of frames, the respective electrical energies of each respective low-frequency audio signal, and wherein determining the electrical energy of the consolidated low-frequency audio signal comprises determining, for the individual frame of the plurality of frames, the electrical energy of the consolidated low-frequency audio signal.

5. The playback device of claim 1 , wherein the plurality of audio drivers includes a first audio driver and a second audio driver, and wherein a value of the threshold frequency is based on a distance between the first and second audio drivers.

6. The playback device of claim 5 , wherein the distance between the first and second audio drivers is an odd-integer multiple of a quarter-wavelength of the threshold frequency.

7. The playback device of claim 1 , wherein adjusting the gain of the consolidated low-frequency audio signal based on both (i) the first energy and (ii) the second energy comprises adjusting the gain of the consolidated low-frequency audio signal according to:

G=E 1 /E 2 ,

wherein G is the gain adjustment of the consolidated low-frequency audio signal, E 1 is the first energy, and E 2 is the second energy.

8. Tangible, non-transitory, computer-readable media storing instructions executable by one or more processors to cause a playback device to perform operations comprising:

receiving a multi-channel audio signal representing multi-channel audio content for playback via the playback device;

separating, from respective channels of the multi-channel audio signal, respective low-frequency audio signals comprising frequencies less than a threshold frequency;

determining respective electrical energies of each respective low-frequency audio signal;

determining a first energy by summing the respective electrical energies of each respective low-frequency audio signal;

consolidating the respective low-frequency audio signals into a consolidated low-frequency audio signal;

determining a second energy by determining an electrical energy of the consolidated low-frequency audio signal;

generating a gain-adjusted low-frequency audio signal by adjusting a gain of the consolidated low-frequency audio signal based on both (i) the first energy and (ii) the second energy;

generating a gain-adjusted multi-channel audio signal by mixing the gain-adjusted low-frequency audio signal back into the respective channels of the multi-channel audio signal; and

using the gain-adjusted multi-channel audio signal to play back gain-adjusted multi-channel audio content via a plurality of audio drivers of the playback device.

9. The tangible, non-transitory, computer-readable media of claim 8 , wherein the multi-channel audio signal comprises a left-channel audio signal, a center-channel audio signal, and a right-channel audio signal, and wherein separating, from the respective channels of the multi-channel audio signal, the respective low-frequency audio signals that are below the threshold frequency comprises:

separating, from the left-channel audio signal, a first low-frequency audio signal comprising first frequencies less than the threshold frequency;

separating, from the center-channel audio signal, a second low-frequency audio signal comprising second frequencies less than the threshold frequency; and

separating, from the right-channel audio signal, a third low-frequency audio signal comprising third frequencies less than the threshold frequency.

10. The tangible, non-transitory, computer-readable media of claim 9 , wherein the first low-frequency audio signal is different than the second and third low-frequency audio signals, and wherein the second low-frequency audio signal is different than the third low-frequency audio signal.

11. The tangible, non-transitory, computer-readable media of claim 8 , wherein the multi-channel audio signal comprises a plurality of frames of audio content, wherein determining the respective electrical energies of each respective low-frequency audio signal comprises determining, for an individual frame of the plurality of frames, the respective electrical energies of each respective low-frequency audio signal, and wherein determining the electrical energy of the consolidated low-frequency audio signal comprises determining, for the individual frame of the plurality of frames, the electrical energy of the consolidated low-frequency audio signal.

12. The tangible, non-transitory, computer-readable media of claim 8 , wherein the plurality of audio drivers includes a first audio driver and a second audio driver, and wherein a value of the threshold frequency is based on a distance between the first and second audio drivers.

13. The tangible, non-transitory, computer-readable media of claim 12 , wherein the distance between the first and second audio drivers is an odd-integer multiple of a quarter-wavelength of the threshold frequency.

14. The tangible, non-transitory, computer-readable media of claim 8 , wherein adjusting the gain of the consolidated low-frequency audio signal based on both (i) the first energy and (ii) the second energy comprises adjusting the gain of the consolidated low-frequency audio signal according to:

G=E 1 /E 2 ,

wherein G is the gain adjustment of the consolidated low-frequency audio signal, E 1 is the first energy, and E 2 is the second energy.

15. A method comprising

receiving, by a playback device, a multi-channel audio signal representing multi-channel audio content for playback via the playback device;

separating, by the playback device, from respective channels of the multi-channel audio signal, respective low-frequency audio signals comprising frequencies less than a threshold frequency;

determining, by the playback device, respective electrical energies of each respective low-frequency audio signal;

determining, by the playback device, a first energy by summing the respective electrical energies of each respective low-frequency audio signal;

consolidating, by the playback device, the respective low-frequency audio signals into a consolidated low-frequency audio signal;

determining, by the playback device, a second energy by determining an electrical energy of the consolidated low-frequency audio signal;

generating, by the playback device, a gain-adjusted low-frequency audio signal by adjusting a gain of the consolidated low-frequency audio signal based on both (i) the first energy and (ii) the second energy;

generating, by the playback device, a gain-adjusted multi-channel audio signal by mixing the gain-adjusted low-frequency audio signal back into the respective channels of the multichannel audio signal; and

using, by the playback device, the gain-adjusted multi-channel audio signal to play back gain-adjusted multi-channel audio content via a plurality of audio drivers of the playback device.

16. The method of claim 15 , wherein the multi-channel audio signal comprises a left-channel audio signal, a center-channel audio signal, and a right-channel audio signal, and wherein separating, from the respective channels of the multi-channel audio signal, the respective low-frequency audio signals that are below the threshold frequency comprises:

separating, from the left-channel audio signal, a first low-frequency audio signal comprising frequencies less than the threshold frequency;

separating, from the center-channel audio signal, a second low-frequency audio signal comprising frequencies less than the threshold frequency; and

separating, from the right-channel audio signal, a third low-frequency audio signal comprising frequencies less than the threshold frequency.

17. The method of claim 15 , wherein the multi-channel audio signal comprises a plurality of frames of audio content, wherein determining the respective electrical energies of each respective low-frequency audio signal comprises determining, for an individual frame of the plurality of frames, the respective electrical energies of each respective low-frequency audio signal, and wherein determining the electrical energy of the consolidated low-frequency audio signal comprises determining, for the individual frame of the plurality of frames, the electrical energy of the consolidated low-frequency audio signal.

18. The method of claim 15 , wherein the plurality of audio drivers includes a first audio driver and a second audio driver, and wherein a value of the threshold frequency is based on a distance between the first and second audio drivers.

19. The method of claim 18 , wherein the distance between the first and second audio drivers is an odd-integer multiple of a quarter-wavelength of the threshold frequency.

20. The method of claim 15 , wherein adjusting the gain of the consolidated low-frequency audio signal based on both (i) the first energy and (ii) the second energy comprises adjusting the gain of the consolidated low-frequency audio signal according to:

G=E 1 /E 2 ,

wherein G is the gain adjustment of the consolidated low-frequency audio signal, E 1 is the first energy, and E 2 is the second energy.