Initially, the stream of essential notes are detected then to be followed by processing for determination of tonal context evolution that ensues from that stream. The system is composed of two modules. The first performs pitch-class note detection. The design principles are chosen for this module to operate on any acoustical musical instrument that has harmonic spectra. Initially, amplitude adjustment is performed on the sampled signal to amplify the lower energy portions of the input .
Spectral information is obtained using a modified constant Q transform and post-filtering.
A multiple fundamental frequency tracking algorithm is applied for extracting and following fundamental frequencies in time. The output of the first module is obtained by transforming the fundamental traces into a sequence of pitch-class notes. The second module calculates tonal context from the pitch-class note stream recognized by the first module. Leaky integrators are used to model recency effects of musical events. Their behavior is controlled locally by the degree of importance of the newly encountered notes as given by Krumhansl's tone-profile data and globally by the external control parameters.