Audio processing device and a method for estimating a signal-to-noise-ratio of a sound signal

A method of estimating an a priori signal to noise ratio ζ(k,n) of a time-frequency representation Y(k,n) of an electric input signal representing a time variant sound signal consisting of target speech components and noise components, where k and n are frequency band and time frame indices, respectively, the method comprising

• determining a first signal to noise ratio estimate γ(k,n) of said electric input signal Y(k,n);
• determining a second signal to noise signal ratio estimate ζ(k,n) of said electric input signal from said first signal to noise ratio estimate γ(k,n) based on a recursive algorithm;
• determining said second signal to noise ratio estimate ζ(k,n) by non-linear smoothing of said first signal to noise ratio estimate γ(k,n), or a parameter derived therefrom, and wherein said non-linear smoothing is controlled by one or more bias and/or smoothing parameters;
• and
• selecting an input to determine said one or more bias and/or smoothing parameters based on a select control parameter;
• wherein said select control parameter for a given frequency index k is determined in dependence of the first and/or the second signal to noise ratio estimates corresponding to a multitude of frequency indices.

An audio processing device, comprising

• at least one input unit for providing a time-frequency representation Y(k,n) of an electric input signal representing a time variant sound signal consisting of target speech signal components S(k,n) from a target sound source TS and noise signal components N(k,n) from other sources than the target sound source, where k and n are frequency band and time frame indices, respectively,
• a noise reduction system configured to
• determine a first signal to noise ratio estimate γ(k,n) of said electric input signal,
• determine second target signal to noise ratio estimate ζ(k,n) of said electric input signal from said first signal to noise ratio estimate γ(k,n) based on a recursive algorithm comprising a recursive loop,
• determine said second signal to noise ratio estimate ζ(k,n) by non-linear smoothing of said first signal to noise ratio estimate γ(k,n), or a parameter derived therefrom, and wherein said non-linear smoothing is controlled by one or more bias and/or smoothing parameters;
• and
• a selector located in the recursive loop, wherein said selector is configured to select an input to determine said one or more bias and/or smoothing parameters based on said select control parameter;
• and
• one or more detectors;
• wherein said select control parameter for a given frequency index is determined in dependence of inputs from said one or more detectors.