Gain and equalization system and method

• US 5,892,833 A
• Filed: 02/05/1998
• Issued: 04/06/1999
• Est. Priority Date: 04/28/1993
• Status: Expired due to Fees

• Current Assignee: Night Technologies International
• Original Assignee: Night Technologies International
• Inventors: Parker, Lance, Jensen, Quinn, Maag, Clifford
• Primary Examiner(s): Kuntz, Curtis A.
• Assistant Examiner(s): Barnie, Rexford N.
• Application Number:
  US09/018,687
• Time in Patent Office: 425 Days
• Field of Search: 381/71.1, 381/94.1, 381/94.3, 381/98, 381/94.7, 381/93, 381/120, 381/121, 381/108, 381/103, 381/124, 333/28 T, 333/28 R, 333/78
• US Class Current: 381/98
• CPC Class Codes: H04R 3/04 for correcting frequency response

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 Y_n, 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 Y_n 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 Y_n1 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 Y_n and Y_n1 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.

Claims

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 Y_n 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 Y_n1 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 Y_n and Y_ni 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.

2. A system as in claim 1 further including analog-to-digital converter means for converting an analog audio signal to the digital audio signal X, for supplying to the digital filter means.

3. A system as in claim 2 further including.

4. A system as in claim 1 wherein the digital filter means each includes means for processing a respective frequency band of the signal X, where the center frequency of each band processed by a digital filter means is separated from adjacent center frequencies of bands processed by other digital filter means, by about two octaves.

5. A system as in claim 1 further including another digital filter means for processing and selectively amplifying/attenuating a frequency band of the signal X which is still higher than the frequency bands processed by the plurality of digital filter means and the additional filter means, to produce an output signal Y_n2 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 wherein said summing means includes means for summing the output signals Y_n, Y_n1, and Y_n2 to produce a resultant digital signal whose waveform of the frequency response is concave upward for the lower frequencies, generally flat at a first level for the central frequencies, and generally flat at a higher second "shelf" level for the higher frequencies.

6. A method of equalizing a received analog audio signal comprising the steps of:

(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.