Under the condition where a plurality of background noise sources exists, there are arranged a first receiver, primarily receiving desired voice, and a plurality of second receivers each primarily receiving noise from a corresponding noise source. Filter coefficients of equivalent noise-producing filters, each having a frequency transmission characteristic equivalent to that of transmission path from its corresponding noise source to the first receiver, are estimated based upon mutual-correlation coefficients among the outputs of the first and second receivers and auto-correlation coefficients of the respective outputs of the second receivers. The noise signals from the equivalent noise-producing filters are subtracted from the output of the first receiver, thereby canceling the background noise. The filter coefficients estimation may be performed by using a maximum of the mutual-correlation coefficients between the outputs of the first receiver and the respective second receivers.
A system for selective sound capture for hands-free telephony and multimedia workstations of the acoustic antenna type with an aerial formed by a member with a concave cylindrical surface. The system includes a plurality of electro-acoustic transducers which are distributed over and in the vicinity of the cylindrical surface. Circuits for partial summation of a plurality of analog sound signals make it possible to form elementary acoustic antennas and a summation circuit produces a resultant analog signal representative of the sound signal arising from a useful speaking area.
A method and apparatus are provided to adaptively form an optimum signal-free reference used to cancel near-field noise in an adaptive plate-noise cancellation system. First, second and third pressure sensors are positioned to detect any near-field plate-radiated noise. The first sensor is positioned closest to the plate, the third sensor is positioned furthest from the plate, and the second sensor is positioned between the first and third sensors. An acoustic far-field projector generates a plurality of broadband signals from a plurality of incidence angles. Each broadband signal is projected at an amplitude indicative of a noise-off condition. Outputs from the first and third sensors are combined to form a dipole responsive to each broadband signal). A feedback system is operatively associated with the dipole and the second sensor. The feedback system includes an adaptive filter that converges to generate an optimum signal-free reference for each of the plurality of the broadband signals and stores filter coefficients indicative of the optimum signal-free reference for each of the broadband signals. Switching means are provided to selectively switch the adaptive filter out of the feedback system such that the stored filter coefficients may be used.
A microphone apparatus having a microphone for producing a desired audio signal, includes an adaptive signal processing section which is supplied with a reference signal based on a vibration detected signal from a vibration detecting circuit in response to a vibration of a vibration generating source whose vibration is picked up by the microphone and becomes an unnecessary noise signal, or in response to a control signal for controlling a drive source of a driving unit of a recording apparatus for recording an output signal from the microphone and which reduces a noise signal contained in the audio signal.
A directional microphone is disclosed. The shotgun microphone has an elongated tube which is designed to control directivity at frequencies above a predetermined frequency and at least four reference microphones spatially arranged about said shotgun microphone. A signal processor, which is electrically connected to said shotgun and reference microphones, generates interference cancelling signals from the portions of the signals from the reference microphones which have frequencies generally below the predetermined frequency. The signal processor combines the cancelling signals with the signal from the shotgun microphone to generate an output signal in which signals originating from in front of the directional microphone in a direction along the longitudinal axis of said tube are enhanced and signals originating from locations other than in front of the directional microphone in a direction along the longitudinal axis of said tube are suppressed.
A noise suppression apparatus has a main microphone for mainly picking up a voice and for outputting an input signal including an audio signal and a first noise component generated from a noise source, a reference microphone for picking up a second noise component generated from the noise source, a filter bank for band-dividing the input signal from the main microphone and the second noise component from the reference microphone, and a noise cancel circuit for obtaining a phase difference between the input signal and the second noise component with respect to each divided band of the filter bank so as to correct the input signal based on the phase difference and for cancelling the first noise component in the input signal by use of the corrected input signal.
