Sound system gain and equalization circuit

• US 5,805,716 A
• Filed: 04/14/1997
• Issued: 09/08/1998
• Est. Priority Date: 04/28/1993
• Status: Expired due to Fees

• Current Assignee: Night Technologies International
• Original Assignee: Night Technologies International
• Inventors: Parker, Lance, Maag, Clifford
• Primary Examiner(s): Isen, Forester W.
• Application Number:
  US08/840,278
• Time in Patent Office: 512 Days
• Field of Search: 381/98, 381/101, 381/104, 381/103, 381/100, 333/28 R, 333/28 T
• US Class Current: 381/98
• CPC Class Codes: H03F 3/68 Combinations of amplifiers, e.g. multi-channel amplifiers for stereophonics power amplifiers using a combination of several semiconductor amplifiers H03F3/211; combinations of amplifiers using coupling networks with distributed constants H03F3/602
• CPC Class Codes: H03G 5/025 Equalizers; Volume or gain control in limited frequency bands
• CPC Class Codes: H03G 9/02 in untuned amplifiers
• CPC Class Codes: H04R 3/04 for correcting frequency response
• CPC Class Codes: H04R 5/04 Circuit arrangements, e.g. for selective connection of amplifier inputs/outputs to loudspeakers, for loudspeaker detection, or for adaptation of settings to personal preferences or hearing impairments combinations of amplifiers H03F3/68; stereophonic systems H04S

Abstract

A multi-band equalizer for receiving and processing an audio signal includes a plurality of operational amplifiers, each for processing a different frequency band of the audio signal to produce an output signal. Each operational amplifier includes an inverting input, a non-inverting input, a resistor means coupled to the non-inverting input for receiving the audio signal and supplying it to the non-inverting input, an output, a feedback circuit coupled between the output and the inverting input for determining the upper limits of the frequency band processed by that particular operational amplifier, and an input circuit coupled between the inverting input and ground potential for determining the lower limits of the frequency band processed by that operational amplifier. An additional operational amplifier is provided for processing a higher frequency band of the audio signal than those processed by the plurality of operational amplifiers, for producing an output signal. The additional operational amplifier includes the same elements as the plurality of operational amplifiers except the feedback circuit which is replaced by a resistor. A summing circuit is coupled to the outputs of all of the operational amplifiers for combining the output signals thereof to produce a resultant signal. The summing circuit includes a plurality of variable resistors, each coupled to the output of a different operational amplifier for selectively varying the magnitude of the output signal from the respective operational amplifiers.

Claims

1. A voltage gain and equalization circuit for processing a received audio signal, comprising

a plurality of operational amplifier means, each for processing and selectively amplifying a different frequency band of the audio signal to produce an output signal, and each including

an inverting input,

a non-inverting input for receiving the audio signal,

an output,

high pass filter means coupled between the inverting input and ground for determining the lower end of the frequency band processed by said each operational amplifier means, and

low pass filter means coupled between the output and the inverting input for determining the upper end of the frequency band processed by said each operational amplifier means,

at least one additional operational amplifier means for processing and selectively amplifying a frequency band of the audio signal, which is higher than the frequency bands processed by the plurality of operational amplifier means, to produce an output signal, said additional operational amplifier means including an inverting input, a non-inverting input for receiving the audio signal, an output, high pass filter means coupled between the inverting input and ground, and resistance means coupled between the output and the inverting input, and

means coupled to the outputs of each operational amplifier means for combining the output signals thereof to produce a resultant signal.

2. A voltage gain and equalization circuit as in claim 1 further including an isolation network for coupling the combining means to a load.

3. A voltage gain and equalization circuit as in claim 1 wherein said combining means comprises a plurality of variable resistance means, each coupled between the output of a respective operational amplifier means and the combining means, for selectively varying the magnitude of the output signal from said respective operational amplifier means.

4. A voltage gain and equalization circuit as in claim 1 wherein each operational amplifier means includes resistance means coupled to the non-inverting input of said each operational amplifier means.

5. A voltage gain and equalization circuit as in claim 4 wherein each high pass filter means comprises a series connection of a first capacitor and a first resistor coupled between the inverting input and ground, wherein the capacitance of the first capacitor and resistance of the first resistor are selected to roll off the low end of a frequency band different from those of the other operational amplifier means.

6. A voltage gain and equalization circuit as in claim 5 wherein each low pass filter means comprises a parallel connection of a second capacitor and a second resistor, wherein the capacitance of the second capacitor and resistance of the second resistor are selected to roll off the high end of a frequency band different from those of the other operational amplifier means.

7. A voltage gain and equalization circuit as in claim 6 wherein the separation between frequency bands processed by the plurality of operational amplifier means is about a factor of four.

8. A voltage gain and equalization circuit as in claim 6 wherein there are six operational amplifier means for processing respective ones of six different bands of the audio signal, where the center frequencies of the respective bands are 10 Hz, 40 Hz, 160 Hz, 640 Hz, 2560 Hz and 10240 Hz, with the skirts varying about 11/2 dB at one octave from the respective center frequency, about 6 dB at two octaves, about 10 dB at three octaves and about 131/2 dB at four octaves.

9. A voltage gain and equalization circuit as in claim 6 wherein the capacitance values of all the first capacitors are substantially the same, and wherein the capacitance values of all the second capacitors are substantially the same.

10. A voltage gain and equalization circuit as in claim 1 further including a second additional operational amplifier means for processing and selectively amplifying a frequency band of the audio signal, which is different from the frequency band processed by said at least one additional operational amplifier means and is higher than the frequency bands processed by the plurality of operational amplifier means.

11. A voltage gain and equalization circuit as in claim 10 wherein the plurality of operational amplifier means comprises four operational amplifier means.

12. A multiple-band equalizer for receiving and processing an audio signal comprising

a plurality of operational amplifier means, each for processing a different frequency band of the audio signal to produce an output signal, and each including

an inverting input,

a non-inverting input,

resistor means coupled to the non-inverting input for receiving the audio signal and supplying it to the non-inverting input,

an output,

feedback circuit means coupled between the output and the inverting input for determining the upper limits of the frequency band processed by said each operational amplifier means, and

input circuit means coupled between the inverting input and ground potential for determining the lower limits of the frequency band processed by said each operational amplifier means,

an additional operational amplifier means for processing frequency band of the audio signal which is higher than the frequency bands processed by said plurality of operational amplifier means, to produce an output signal, said additional operational amplifier means including an inverting input, a non-inverting input, resistor means coupled to the non-inverting input, an output, resistor means coupled between the output and the inverting input, and input circuit means coupled between the inverting input and ground potential, and

summing circuit means coupled to the outputs of each operation amplifier means for combining the output signals thereof to produce a resultant signal.

13. An equalizer as in claim 12 wherein said summing circuit includes a plurality of variable resistance means, each coupled to the output of a different operational amplifier means for selectively varying the magnitude of the output signal from said respective operational amplifier means.

14. An equalizer as in claim 13 wherein each feedback circuit means includes a parallel connection of a capacitor and a resistor, and wherein each input circuit means includes a series connection of a capacitor and a resistor.

15. A voltage gain and equalization circuit for processing a received audio signal, comprising

a plurality of operational amplifier means, each for processing and selectively amplifying a different frequency band of the audio signal to produce an output signal, and each including

an inverting input,

a non-inverting input for receiving the audio signal,

an output,

high pass filter means coupled between the inverting input and ground for determining the lower end of the frequency band processed by said each operational amplifier means,

low pass filter means coupled between the output and the inverting input for determining the upper end of the frequency band processed by said each operational amplifier means, and

means coupled to the outputs of each operational amplifier means for combining the output signals thereof to produce a resultant signal.

16. A voltage gain and equalization circuit as in claim 15 further including an isolation network for coupling the combining means to a load.

17. A voltage gain and equalization circuit as in claim 15 wherein said combining means comprises a plurality of variable resistance means, each coupled between the output of a respective operational amplifier means and the combining means, for selectively varying the magnitude of the output signal from said respective operational amplifier means.

18. A voltage gain and equalization circuit as in claim 15 wherein each operational amplifier means includes resistance means coupled to the non-inverting input of said each operational amplifier means.

19. A voltage gain and equalization circuit as in claim 18 wherein each high pass filter means comprises a series connection of a first capacitor and a first resistor coupled between the inverting input and ground, wherein the capacitance of the first capacitor and resistance of the first resistor are selected to roll off the low end of a frequency band different from those of the other operational amplifier means.

20. A voltage gain and equalization circuit as in claim 19 wherein each low pass filter means comprises a parallel connection of a second capacitor and a second resistor, wherein the capacitance of the second capacitor and resistance of the second resistor are selected to roll off the high end of a frequency band different from those of the other operational amplifier means.

21. A voltage gain and equalization circuit as in claim 20 wherein the separation between frequency bands processed by the plurality of operational amplifier means is about a factor of four.

22. A voltage gain and equalization circuit as in claim 20 wherein there are six operational amplifier means for processing respective ones of six different bands of the audio signal, where the center frequencies of the respective bands are 10 Hz, 40 Hz, 160 Hz, 640 Hz, 2560 Hz and 10240 Hz, with the skirts varying about 11/2 dB at one octave from the respective center frequency, about 6 dB at two octaves, about 10 dB at three octaves and about 131/2 dB at four octaves.

23. A voltage gain and equalization circuit as in claim 20 wherein the capacitance values of all the first capacitors are substantially the same, and wherein the capacitance values of all the second capacitors are substantially the same.

24. A multiple-band equalizer for receiving and processing an audio signal comprising

a plurality of operational amplifier means, each for processing a different frequency band of the audio signal to produce an output signal, and each including

an inverting input,

a non-inverting input,

resistor means coupled to the non-inverting input for receiving the audio signal and supplying it to the non-inverting input,

an output,

feedback circuit means coupled between the output and the inverting input for determining the upper limits of the frequency band processed by said each operational amplifier means, and

input circuit means coupled between the inverting input and ground potential for determining the lower limits of the frequency band processed by said each operational amplifier means, and

summing circuit means coupled to the outputs of each operation amplifier means for combining the output signals thereof to produce a resultant signal.

25. An equalizer as in claim 24 wherein said summing circuit includes a plurality of variable resistance means, each coupled to the output of a different operational amplifier means for selectively varying the magnitude of the output signal from said respective operational amplifier means.

26. An equalizer as in claim 25 wherein each feedback circuit means includes a parallel connection of a capacitor and a resistor, and wherein each input circuit means includes a series connection of a capacitor and a resistor.

27. A combination preamplifier/equalizer for processing audio signals received from microphones and the like comprising

a plurality of operational amplifier means for selectively amplifying a different frequency band of the audio signals to produce an output signal, each operational amplifier means including an inverting input, a non-inverting input, an output, and resistor means for receiving the audio signals and supplying them to the non-inverting input,

a plurality of variable resistor means, each coupled to the output of a different operational amplifier means, and

summing circuit means coupled to each of the variable resistor means for combining the output signals of the operational amplifier means to produce a resultant signal.

28. The combination of claim 27 wherein each operation amplifier means comprises

feedback means coupled between the output and inverting input of said each operational amplifier means, and including a parallel connection of a capacitor and a resistor, and

input means coupled between the inverting input of said each operational amplifier means and ground potential, and including a series connection of a capacitor and a resistor.