System for dynamic spectral correction of audio signals to compensate for ambient noise

An apparatus (200), effective in producing corrections to an audio signal which is a signal of interest, across a spectrum of frequencies, by applying corrective gains of amplitude to a plurality of frequency components which constitute the audio signal, wherein parallel compression is used to approximate gain curves derived from a psychoacoustic model, wherein the parallel compression is implemented by applying a gain G at a particular frequency component of the audio signal according to a linear compression and then combining this compressed signal with the audio signal, such that the combined parallel compression of the audio signal forms a non-linear compression curve, where the linear compression is found by the equation, G=g0+(P−T)*(1/R−1) where G is the gain in dB to be applied to the audio signal, where g0 is a makeup gain in dB, T is a threshold in dB, and R is a compression ratio, and where P is a sound intensity in dB of the audio signal at a frequency component, such that g0, T, and R are parameters that vary the shape of a resulting parallel compression curve, where the psychoacoustic model takes as inputs the audio signal loudness and an ambient noise signal loudness, where the model computes the gain in sound loudness, at a given frequency component, required to correct for the effect of the ambient noise signal, where the parameters g0, T, and R, for a plurality of noise loudness levels, are predetermined by fitting the parallel compression curves against the desired behavior, where a different set of parameters is retrieved at each instant depending on the ambient noise volume at each frequency component, where the dynamically changing noise loudness results in a dynamically changing selection of parameters for the parallel compression module, the apparatus (200) comprising:

• (a) a first audio device (202), configured to extract a first audio signal (002) where the first audio signal is a broadband audio signal of interest, the first audio device operatively connected to a microprocessor (201);
• (b) a second audio device (203), configured for extracting a second audio signal (003) where the second audio signal (003) is ambient broadband noise audio in the environment, the second audio device (203) operatively connected to the microprocessor (201);
• (c) the microprocessor (201), configured to execute applications for:
• i. a first frequency analysis module (204), configured to extract a plurality of frequency components from the first audio signal (002), ii. a second frequency analysis module (205), configured to extract a plurality of frequency components from the second audio signal (003), iii. a first power estimation block (206), configured to calculate a sound intensity in decibels of each frequency component of the first audio signal (002), iv. a second power estimation block (207), configured to calculate a sound intensity of decibels of each frequency component of the second audio signal (003), v. a parameter estimation module (211), which determines parameter settings for a parallel compression module, according to information stored in memory, vi. the parallel compression module (209), parameterized by parameters including a threshold T, a compression ratio R, and a makeup gain g0, where said parameters may by dynamically varied, where the parallel compression module is comprised of:
• a. a linear compression module (112), which, using the parameters applies gains to the first audio signal according to the equation G=g0+(P−T)*(1/R+1), where G is the gain in dB to be applied to a frequency component of the first audio signal, P is the sound intensity of the first signal at the frequency component in dB, g0 is the makeup gain in dB, T is the threshold in dB, and R is the compression ratio of the linear compression, b. a summer (110), which combines the resulting amplified first audio signal component with the original first audio signal component, vii. a Frequency Synthesis Module (210), which combines the frequency components of the resulting first audio signal, wherein (i) the first audio device (202) extracts the first audio signal (002), whereupon the first audio signal (002) is then transmitted through a first analog to digital converter (71), thereby converting the first audio signal (002) into digital format, and simultaneously, (ii) the second audio device (203) extracts the second audio signal (003), where said second audio signal (003) is then transmitted through a second analog to digital converter (72) thereby converting the second audio signal (003) into digital format, whereupon the first audio signal x(t) (002) and the second audio signal xo(t) (003) are fed, respectively, through the First Frequency Analysis Module (204) and Second Frequency Analysis Module (205) breaking down each respective audio signal into arrays of frequency components, whereupon, for each frequency component, the first audio signal (002) and the second audio signal (003) are fed, respectively, through the first Power Estimation Block (206) and Second Power Estimation Block (207), resulting in estimates, for each frequency component, and at each instant, for the sound intensity of each signal in decibels, whereupon, for each frequency component, and at each instant, the microprocessor (201), using the power estimates of the frequency components of the first (002) and second (003) audio signals, obtains parameters for parallel compression (211), depending on the sound intensity of the second audio signal (003) at each instant, whereupon the microprocessor (201), applies the parameters to the parallel compression module (209), whereupon the parallel compression module (209) applies linear compression, according to the selected parameters, to each of the frequency components of the first audio signal (002), whereupon the parallel compression module (209) sums each frequency component of the first audio signal (002) with the corresponding compressed audio signal, whereupon the microprocessor (201) repeats the process of estimating the power of both the first audio signal and the second audio signal, selecting compression settings, and applying parallel compression for each frequency component of the first audio signal (002), whereupon the microprocessor (201) reconstitutes the first audio signal (002) by feeding the now parallel compressed frequency components of the parallel compressed first audio signal (002) through the Frequency Synthesis Module (210), thereby obtaining an output Xout (t).