Determining a Harmonicity Measure for Voice Processing

A method of operating a processing apparatus to determine a measure of harmonicity of an audio signal, the method comprising:

• accepting the audio signal;
• determining a spectrum of an amplitude measure for a set of frequencies, including time-to-frequency transforming the signal to form a set of frequency components of the signal at the set of frequencies;
• and
• determining as a measure of harmonicity a quantity indicative of the normalized difference of spectral content in a first subset of frequencies corresponding to harmonic components of the audio signal and the sum of the spectral content in a second subset of frequencies corresponding to inharmonic components of the audio signal, the difference normalized by the sum of spectral content in the first and second subsets, all spectral contents being up to a maximum frequency and based on the amplitude measure.

An apparatus to determine a measure of harmonicity of an audio signal, the apparatus comprising:

• a spectrum calculator operative to accept the audio signal and calculate a spectrum of an amplitude measure for a set of frequencies, the spectrum calculator including a transformer to time-to-frequency transform the signal;
• a fundamental frequency selector operative to determine a candidate fundamental frequency in a range of frequencies;
• a mask determining element coupled to the fundamental frequency selector and operative to retrieve or calculate an associated mask for the candidate fundamental frequency;
• a harmonicity measure calculator operative to determine a measure of harmonicity for the candidate fundamental frequency by determining the sum over the set of frequencies up to a maximum frequency of the product of the associated mask and the amplitude measure, divided by the sum over the set of frequencies up to the maximum frequency of the amplitude measure;
• a maximum selector operative to select the maximum of candidate harmonicity measures determined by the harmonicity measure calculator for candidate fundamental frequencies in the range of frequencies.