A method of classifying an audio signal, comprising: extracting one or more features from the audio signal; and classifying the audio signal according to the extracted features, wherein the extraction of the features comprises: generating at least two measures of harmonicity of the audio signal based on frequency ranges defined by different expected maximum frequencies; and calculating one of the features as a difference or a ratio between the harmonicity measures, wherein the generation of each harmonicity measure based on a frequency range comprises: calculating a log amplitude spectrum of the audio signal based on the frequency range; deriving a first spectrum by calculating each component of the first spectrum as a sum of components of the log amplitude spectrum on frequencies which, in linear frequency scale, are odd multiples of the component's frequency of the first spectrum; deriving a second spectrum by calculating each component of the second spectrum as a sum of components of the log amplitude spectrum on frequencies which, in linear frequency scale, are even multiples of the component's frequency of the second spectrum; deriving a difference spectrum by subtracting the first spectrum from the second spectrum; and generating a measure of harmonicity as a monotonically increasing function of the maximum component of the difference spectrum within a predetermined frequency range. extracting one or more features from the audio signal; and classifying the audio signal according to the extracted features, wherein the extraction of the features comprises: generating at least two measures of harmonicity of the audio signal based on frequency ranges defined by different expected maximum frequencies; and calculating one of the features as a difference or a ratio between the harmonicity measures, generating at least two measures of harmonicity of the audio signal based on frequency ranges defined by different expected maximum frequencies; and calculating one of the features as a difference or a ratio between the harmonicity measures, wherein the generation of each harmonicity measure based on a frequency range comprises: calculating a log amplitude spectrum of the audio signal based on the frequency range; deriving a first spectrum by calculating each component of the first spectrum as a sum of components of the log amplitude spectrum on frequencies which, in linear frequency scale, are odd multiples of the component's frequency of the first spectrum; deriving a second spectrum by calculating each component of the second spectrum as a sum of components of the log amplitude spectrum on frequencies which, in linear frequency scale, are even multiples of the component's frequency of the second spectrum; deriving a difference spectrum by subtracting the first spectrum from the second spectrum; and generating a measure of harmonicity as a monotonically increasing function of the maximum component of the difference spectrum within a predetermined frequency range. calculating a log amplitude spectrum of the audio signal based on the frequency range; deriving a first spectrum by calculating each component of the first spectrum as a sum of components of the log amplitude spectrum on frequencies which, in linear frequency scale, are odd multiples of the component's frequency of the first spectrum; deriving a second spectrum by calculating each component of the second spectrum as a sum of components of the log amplitude spectrum on frequencies which, in linear frequency scale, are even multiples of the component's frequency of the second spectrum; deriving a difference spectrum by subtracting the first spectrum from the second spectrum; and generating a measure of harmonicity as a monotonically increasing function of the maximum component of the difference spectrum within a predetermined frequency range.