Noise reduction device, program and method

An information storage device comprising a noise reduction program that when executed by a central processing unit causes a computer to execute:

• converting surrounding sounds from a first observed signal in a frequency domain into a form of an electric signal, wherein the sounds comprise stationary and non-stationary noise components;
• receiving as a first reference signal an output signal transmitted from an input source to an output source and converting said first reference signal to a second reference signal in a form of a power spectrum in each of multiple predetermined time frames;
• a procedure for calculating a predetermined constant by use of an adaptive coefficient for the constant, calculating a predetermined first reference signal in the frequency domain by use of an adaptive coefficient for the reference signal, and thereby obtaining estimated values respectively of stationary noise components included in a predetermined observed signal in the frequency domain and non-stationary noise components corresponding to the first reference signal;
• a procedure for performing a noise reduction process on the first observed signal on the basis of each of the estimated values, and updating each of the adaptive coefficients on the basis of a result of the noise reduction process;
• a procedure for converting the first observed signal to a second observed signal in a form of a power spectrum in each of a plurality of predetermined time frames;
• and
• an adaptive procedure for repeating the obtaining of the estimated values and the updating of the adaptive coefficients, and thereby learning each of the adaptive coefficients;
• wherein the adaptive coefficient to be used for calculating estimated values respectively of the stationary noise components and the non-stationary noise components is designed to be learned on a basis of the second observed signal and the second reference signal in the frequency domain at a same time.

A noise reduction method comprising the steps of:

• using a microphone for converting surrounding sounds to a first observed signal in a frequency domain into a form of an electric signal, wherein the sounds comprise stationary and non-stationary noise components;
• using a discrete transform unit for receiving as a first reference signal an output signal transmitted from an input source to an output source and converting said first reference signal to a second reference signal in a form of a power spectrum in each of the predetermined time frames;
• obtaining a reference signal which is a consequence of converting a signal corresponding to sound emitted from a source of non-stationary noise to a signal in the frequency domain;
• calculating a predetermined constant by use of an adaptive coefficient for the constant, calculating a predetermined reference signal in the frequency domain by use of an adaptive coefficient for the reference signal, and thereby obtaining estimated values respectively of stationary noise components included in the observed signal and non-stationary noise components based on a sound wave from the source of non-stationary noise;
• performing a noise reduction process on the first observed signal on the basis of each of the estimated values, and updating each of the adaptive coefficients on the basis of a result of the noise reduction process
• repeating the obtaining of the estimated values and the updating of the adaptive coefficients, and thereby learning each of the adaptive coefficients;
• and
• converting the first observed signal to a second observed signal in a form of a power spectrum in each of a plurality of predetermined time frames;
• wherein the adaptive coefficient to be used for calculating estimated values respectively of the stationary noise components and the non-stationary noise components is designed to be learned on a basis of the second observed signal and the second reference signal in the frequency domain at a same time.