Amplifier with multifilter

Abstract

In an audio amplifier for amplifying signals from an electric guitar or the like having a conventional tone control circuit for selectively emphasizing input signals in the bass, middle and treble frequency ranges of the instrument, a multifilter circuit for emphasizing input signals with frequencies in selected, relatively narrow, frequency bands in the upper portion of the frequency spectrum to minimize aural fatigue. The multifilter circuit comprises a plurality of parallel connected, two-pole, resonant filter sections with different, relatively narrow, resonant frequency bands separated from one another by an amount on the order of 1/4 octave and forms a signal path that supplements the signal path provided by the conventional tone control circuit. The signals produced on the output of the tone control circuit are mixed with the multifilter output signals. Potentiometers are provided to vary the amplitude of the output signals of the entire multifilter circuit or selected ones of the filter sections thereof. Both the amplitude and phase frequency response of the multifilter are characterized by a plurality of successive peaks and dips, such that as the musician plays different notes, certain number of harmonics are emphasized in some notes, while other harmonics are emphasized in other notes with respect to amplitude while variations in the pitch or frequency of the input signal result in the phases of the individual harmonics to be rapidly shifted which causes minute shifts in the pitch of the individual harmonics produced on the output.