Abstract: An automatic equalizer sequentially adds subdued narrow band audio reference signals of different frequencies to an audio program signal being broadcast, and measures the magnitude of each successive broadcast reference signal to determine a measured frequency response of an audio amplification system and its environment. The gains, or attenuations, of various frequency bands in the broadcast signal are adjusted as needed to produce a desired frequency response. In one embodiment the added reference signals are masked by adding the reference signals only when the test frequency is adjacent to a relatively large magnitude frequency component of the program signal. Additional masking is performed by the reference signal being relative quiet and of a short duration such as two to twenty cycles. A narrow band notch filter operates in synchronism with the reference signal adder to eliminate any program signal component at the frequency of each reference signal being added.

Abstract: An electronic tuning device has selectable width tuning ranges wherein selected pairs of the LEDs in a single row of LED's are activated, such as being turned on, blinked or flashed, so that the spacing between each activated pair of LEDs indicates the width of the tuning range during a range indicating mode. The sensing of a fundamental frequency of an input tone causes the operation of a corresponding LED in the row of LEDs to indicate the nearest note along with in-tune and out-of-tune conditions.

Abstract: An electronic tuning device includes a display with a single row of LED's corresponding to musical notes wherein the sensing of a fundamental frequency of an input tone causes the operation of the corresponding LED to indicate the nearest note. Additionally the LED is operated in manner, such as blinking proportionally to the variation from the note and/or producing different colors, such as green, red and amber, to indicate in-tune and out-of-tune conditions. A double back adhesive rubber pad can be used to removably mount the tuner on an instrument, so that the device can simply pulled off the musical instrument to make it ready for its next use. The rubber pad serves to attenuate high frequency mechanical vibrations of the musical instruments thus improving the accuracy and versatility of the unit. In one embodiment, the display is mounted externally on the musical instrument while the tone sensing circuitry is mounted inside the musical instrument such within the sound box of an existing guitar.

Abstract: Audio signals are digitized and an FFT is conducted on samples of the digitized signals to produce corresponding frequency spectrums. These spectrums are analyzed, such as by determining one or more peak frequency magnitudes which are 33 dB greater than harmonics or subharmonics of the frequency in a plurality of several successive spectrums, to detect resonating feedback frequencies. The offending frequency is then filtered in the time domain, either in the digitized form or analog form, to eliminate the feedback.