System for increasing perceived loudness of speakers
A system can be provided for increasing loudness of an audio signal to present a perceived loudness to a listener that is greater than a loudness provided natively by a loudspeaker. The system can include one or more of the following: a frequency suppressor, a loudness adjuster, an equalizer, and a distortion control module. The frequency suppressor can increase headroom in the audio signal by filtering out low and/or high frequencies. The loudness adjuster can calculate a loudness of the audio signal and apply a gain to the audio signal to increase the loudness. The equalizer can further increase headroom by attenuating portions of a passband of the loudspeaker's frequency response. The distortion control module can induce partial harmonic distortion in the audio signal to further increase loudness.
1. A method of limiting an audio signal, the method comprising:
under control of a hardware processor,
receiving an input audio signal;
applying a limiter to the input audio signal to produce a limited audio signal; and
applying a clipping reduction to the limited audio signal to increase signal energy in the limited audio signal compared to the input audio signal, the clipping reduction comprising mapping the limited audio signal into a data structure to produce an output signal, the data structure comprising values representing a sum of sine waves; and
outputting the output signal to a speaker.
2. The method of claim 1 , wherein said applying the clipping reduction further comprises mapping a value of the input audio signal m, m being an integer, to an output sample at an index m in the sum-of-sines table.
3. The method of claim 1 , wherein said applying the clipping reduction further comprises interpolating between two samples in the sum-of-sines table.
4. The method of claim 1 , wherein the values of the sum-of-sines table comprise a sum of odd harmonics.
5. The method of claim 1 , wherein the values of the sum-of-sines table comprise a sum of even harmonics.
6. The method of claim 1 , wherein the values of the sum-of-sines table comprise a sum of two harmonically-related sine waves, three harmonically-related sine waves, four harmonically-related sine waves, or five harmonically-related sine waves.
7. The method of claim 1 , wherein the sum-of-sines table is one of a plurality of sum-of-sines tables.
8. The method of claim 7 , further comprising selecting the sum-of-sines table from the plurality of sum-of-sines tables prior to said applying, said selecting based upon whether the input audio signal includes a voice signal.
9. The method of claim 8 , wherein when the input audio signal includes a voice signal, said selecting comprises selecting one of the plurality of sum-of-sines tables created from fewer harmonics than other of the plurality of sum-of-sines tables created from more harmonics.
10. The method of claim 1 , wherein the sum of sine waves are sums of portions of sine waves.
11. A system limiting an audio signal, the system comprising:
a limiter that receives an input audio signal and that produces a limited audio signal from the input audio signal; and
a distortion control module that uses a hardware processor to:
apply a clipping reduction to the limited audio signal to increase signal energy in the limited audio signal compared to the input audio signal, by at least mapping the limited audio signal into a data structure to produce an output signal, the data structure comprising values representing a sum of portions of sine waves; and
output the output signal to a speaker.
12. The system of claim 11 , wherein the portions of sine waves are quarter sine waves.
13. The system of claim 11 , wherein said mapping comprises applying a mapping function, and wherein said applying the mapping function comprises first reversing the mapping function across an x-axis and inverting the mapping function across a y-axis for negative values of the limited audio signal.
14. The system of claim 11 , further comprising a user interface that provides a distortion control for a user to adjust the amount of said clipping reduction.
15. The system of claim 11 , wherein the portions of sine waves comprise harmonics at about 400 Hz, about 1200 Hz, about 2000 Hz, about 2800 Hz, and about 3600 Hz.
16. The system of claim 11 , wherein the portions of sine waves comprise a first harmonic, a third harmonic, a fifth harmonic, a seventh harmonic, and a ninth harmonic.
17. The system of claim 11 , wherein the portions of sine waves comprise harmonics, which decrease in amplitude monotonically.