Audio enhancement system

Abstract

A stereo enhancement system processes the difference signal component generated from a pair of left and right input signals to create a broadened stereo image reproduced through a pair of speakers or through a surround sound system. Processing of the difference signal component occurs through equalization characterized by amplification of the low and high range of auditory frequencies. The processed difference signal is combined with a sum signal, generated from the left and right input signals, and the original left and right input signals to create enhanced left and right output signals.

1 . A method of enhancing two-channel audio, the method comprising:
 receiving left and right audio inputs;   combining the left and right audio inputs to produce sum information;   combining the left and right audio inputs to produce difference information, the difference information comprising ambient content;   applying a high-pass filter to the difference information with processor circuitry, said high-pass filter configured to attenuate at least a portion of audible bass frequencies of the difference information and to emphasize high-frequency components of the difference information, wherein the high-pass filter is configured to selectively enhance the ambient content so as to encompass a listener within an expanded sound stage;   applying a low-pass filter to the difference information, said low-pass filter configured to attenuate mid-range frequencies of the difference information so as to reduce the listener's sensitivity to the difference information based on the position of the listener's head;   said high-pass filter and said low-pass filter together being characterized at least partly by a magnitude frequency response that emphasizes frequencies in low and high frequency ranges and that deemphasizes frequencies in a mid-frequency range;   combining the filtered difference information, the sum information, and the left audio input to produce a left audio output; and   combining the filtered difference information, the sum information, and the right audio input to produce a right audio output.   
   
   
       2 . The method of  claim 1 , wherein the magnitude frequency response further comprises a gain within a range of about 20 Hz to about 150 Hz that is higher than a minimum gain within a range of about 1 kHz to about 4 kHz. 
   
   
       3 . The method of  claim 1 , further comprising adjusting a level of the sum information. 
   
   
       4 . The method of  claim 1 , further comprising adjusting a level of the difference information. 
   
   
       5 . A system for enhancing two-channel audio, the system comprising:
 a first summing component configured to receive left and right audio inputs and to combine the left and right audio inputs to produce sum information;   a second summing component configured to receive the left and right audio inputs and to combine the left and right audio inputs to produce difference information, the difference information comprising ambient content;   an equalizer filter implemented with one or more processors, the equalizer filter configured to spectrally-shape the difference information by at least:
 attenuating at least a portion of audible bass frequencies in the difference information, 
 attenuating mid-range frequencies in the difference information so as to reduce the listener's sensitivity to the difference information based on the position of the listener's head, and 
 emphasizing high-frequency components in the difference information; 
   a third summing component configured to combine the filtered difference information, the sum information, and the left audio input to produce a left audio output; and   a fourth summing component configured to combine the filtered difference information, the sum information, and the right audio input to produce a right audio output.   
   
   
       6 . The system of  claim 5 , wherein the magnitude frequency response further comprises a gain in a range of about 20 Hz to about 150 Hz that is higher than a minimum gain in a range from about 1 kHz to about 4 kHz. 
   
   
       7 . The system of  claim 5 , wherein the equalizer filter comprises a high-pass filter and a low-pass filter. 
   
   
       8 . The system of  claim 5 , wherein the equalizer filter comprises a band-reject filter. 
   
   
       9 . The system of  claim 5 , further comprising a level adjuster configured to adjust a level of the sum information. 
   
   
       10 . The system of  claim 5 , further comprising a level adjuster configured to adjust a level of the difference information.