Multiple instrument tracking based on reconstruction error, pitch continuity and instrument activity

We present an algorithm for tracking individual instruments in polyphonic music recordings. The algorithm takes as input the instrument identities of the recording and uses non-negative matrix factorisation to compute an instrument-independent pitch activation function. The Viterbi algorithm is applied to find the most likely path through a number of candidate instrument and pitch combinations in each time frame. The transition probability of the Viterbi algorithm includes three different criteria: the frame-wise reconstruction error of the instrument combination, a pitch continuity measure that favours similar pitches in consecutive frames, and the activity status of each instrument. The method was evaluated on mixtures of 2 to 5 instruments and outperformed other state-of-the-art multi-instrument tracking methods.