Gain and equalization system and method
First Claim
1. A gain and equalization system for processing a received digital audio signal X, comprisinga plurality of digital filter means each for processing and selectively amplifying/attenuating a different frequency band of the signal X, to produce an output signal Yn in which the waveform of the frequency response is concave downward for the central frequencies of the band and concave upward for the frequencies above and below the central frequencies,an additional digital filter means for processing and selectively amplifying/attenuating a frequency band of the signal X, the additional digital filter means having a digital feedback circuit with only a resistor to thereby pass a frequency which is higher than the frequency bands processed by the plurality of digital filter means, to produce an output signal Yn1 whose waveform of the frequency response is concave upward for the lower frequencies of the band, concave downward for the low to central frequencies of the band, and generally flat for the central to high frequencies of the band, andmeans for summing the output signals Yn and Yni to produce a resultant digital signal whose waveform of the frequency response is concave upward for the lower frequencies, and generally flat for the remaining frequencies.
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Abstract
A multi-band digital gain and equalizer system for receiving and processing an audio signal includes an analog-to-digital converter for converting the audio signal to a digital signal X, a plurality of digital filters, each for processing and selectively amplifying/attenuating a different frequency band of the signal X, to produce an output signal Yn, in which the waveform of the frequency response is concave downward for the central frequencies of the band and concave upward for the frequencies above and below the central frequencies, a summing circuit for summing the output signals Yn to produce a resultant digital signal, and a digital-to-analog converter for converting the resultant digital signal to a resultant analog audio signal. The center frequencies of each band processed by a digital filter is separated from adjacent center frequencies of bands processed by other digital filters, by about two octaves. An additional digital filter is provided for processing a frequency band of the signal X which is higher than the frequency bands processed by the plurality of digital filters, to produce an output signal Yn1 whose waveform of the frequency response is concave upward for the lower frequencies of the band, concave downward for the low to central frequencies of the band, and generally flat for the higher frequencies of the band. The summing circuit sums the output signals Yn and Yn1 to produce an output signal whose frequency response is substantially flat, with a "floor" at the low end of the frequencies and a "shelf" at the high end of the frequencies, and with little phase shift.
50 Citations
6 Claims
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1. A gain and equalization system for processing a received digital audio signal X, comprising
a plurality of digital filter means each for processing and selectively amplifying/attenuating a different frequency band of the signal X, to produce an output signal Yn in which the waveform of the frequency response is concave downward for the central frequencies of the band and concave upward for the frequencies above and below the central frequencies, an additional digital filter means for processing and selectively amplifying/attenuating a frequency band of the signal X, the additional digital filter means having a digital feedback circuit with only a resistor to thereby pass a frequency which is higher than the frequency bands processed by the plurality of digital filter means, to produce an output signal Yn1 whose waveform of the frequency response is concave upward for the lower frequencies of the band, concave downward for the low to central frequencies of the band, and generally flat for the central to high frequencies of the band, and means for summing the output signals Yn and Yni to produce a resultant digital signal whose waveform of the frequency response is concave upward for the lower frequencies, and generally flat for the remaining frequencies.
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6. A method of equalizing a received analog audio signal comprising the steps of:
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(a) sampling the received analog audio signal to develop a corresponding digital audio signal X; (b) providing a plurality of digital filters, each for processing and selectively amplifying/attenuating a different frequency band of the signal X, to produce an output signal Y(n)=a0 X n!+a1 X n-1!+a2 X n-2!+b1 Y n-1!+b2 Y n-2!, where n is the sample identification of the analog signal, X is the value of the sample supplied to the digital filters, and a0, a1, a2, b1, and b2 are filter co-efficients representing impedances of an equivalent analog operational amplifier circuit suitable for producing the output signal Y(n) in which the waveform of the frequency response is concave downward for the central the central frequencies of the band and concave upward for the frequencies above and below the central frequencies; (c) summing the plurality of output signals Y(n) to produce a resultant digital signal; and (d) converting the resultant digital signal to a resultant analog audio signal.
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Specification