Audio signal equalizer having accelerated slope phase shift compensated filters
AssigneeRane Corporation
InventorDennis A. Bohn
Life of this patent
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Abstract
A tone control shelving equalizer providing low shelf (bass) boost and cut, and high shelf (treble) boost and cut is disclosed wherein the active filter stages provide sharpened (accelerated) amplitude versus frequency response characteristics at the band transitions to leave the center frequencies uncorrupted by out-of-band effects of the tone controls while maintaining circuit stability and avoiding dropouts due to excessive filter phase shifts. Each high and low end band filter network has multiple poles and offset zeros located at a frequency offset so as to restrict the maximum phase shift of the filter to within a safe level not greater than about 90.degree..
Claims19
A bass and treble audio tone control circuit for changing amplitude versus frequency response in low and high bands respectively on opposite ends of a mid-band, comprising:
- bass boost/cut shelving filter means and filter output setting control means therefor;
- treble boost/cut shelving filter means and filter output setting control means therefor;
- at least one of said filter means having n poles and n-1 compensation zeros, wherein n is any integer of 2 or more, said n poles positioned to cause a substantially n pole amplitude versus frequency response in a transition band adjacent one end of said mid-band, and said n-1 zeros being offset toward said mid-band from said n poles so as to cause substantial cancellation of n-1 poles in said mid-band, whereby the amplitude versus frequency response in said mid-band is substantially unaffected by changes in settings of said output setting control means.
An active equalizer circuit for controllably altering the amplitude versus frequency response characteristics of an audio signal having a frequency range that includes a mid-band and an adjacent band, high or low thereto, that is to be controllably altered in relative amplitude, comprising:
- a filter means for said adjacent band, and means for controllably setting signal output for said filter means, said filter means having at least first and second poles and at least one compensation zero, said first and second poles and said at least one compensation zero selected in value so as to cause a multiple-pole frequency dependent amplitude change in said adjacent band and wherein said at least one compensation zero is at an offset from said poles so as to cause cancellation of one of said poles for frequencies approaching and within said mid-band, whereby the multiple poles provide a sharper amplitude versus frequency change in said adjacent band without causing excessive phase shift of the audio signal at the frequencies occupying said mid-band.
Dependencies are inferred from the claim text.