Recognition of musical chord notes

We developed a new algorithm for automatic recognition of musical chord notes. In the chord recognition field, we often refer to the “Chord Spectrum”, that is the chord representation in the frequency domain. The main concept on which the “chord recognition” theory is based is that we need to find similar groups of sinusoidal tones (tone patterns) belonging to the chord spectrum, through which we can describe the chord as an acoustic profile, with the help of “generative subspectra”. The work done by A. Tanguiane during last decade was the starting point to our study that considers chords played by one or more instruments. In his research, Tanguiane described the chord features and used the information taken from the autocorrelation of chord frequency components to recognize it. He considered that partials forming the chord was equally spaced in a logarithmic way in the frequency domain, implying equal distances correspond to equal musical intervals. To obtain the components equally spaced in a logarithmic way, we use the QFT (Q-constant Fourier Transform), introduced by J.C. Brown in 1991, and also used for the recognition of the fundamental frequency of each note. The QFT allows to show the energy of the singular frequencies in a logarithmic scale spectrum. Autocorrelation is evaluated over the components of the QFT that exceed a certain threshold value. The developed algorithm allows us to obtain good results both for recognition of two, three and four notes chords.