A graphical user interface for facilitating generation of an accompaniment for a recorded audio melody is described. A Hidden Markov Model, trained with blended chord transition matrices and melody observation matrices, is used for providing the accompaniment for the recorded audio melody. The recorded audio melody includes segments. Frequency analysis of the recorded audio melody is performed. The total duration of each fundamental frequency within a segment of the melody is summed. Based on the summing, a probability for each possible chord for each segment is computed. Based on the computed probabilities, a set of chords are selected for the segments. The chords are displayed on a chord chart of the graphical user interface. The graphical user interface facilitates various manipulations using the chords and/or controls, and generation of a new accompaniment for a recorded audio melody based on the manipulations.