In this paper we introduce a new approach for realtime multiple pitch observation of musical instruments. The proposed algorithm is quite different from others in the literature both in its purpose and approach. It is destined not for continuous multiple f0recognition but rather for projection of the ongoing spectrum to learned pitch templates. The decomposition algorithm on the otherhand, does not compromise signal processing models for pitches and consists of an algorithm for efficient decomposition of a spectrum using known pitch structures and based on sparse non-negative constraints. After introducing the algorithm along with evaluations,a real-time implementation of the algorithm is provided for free download on the MaxMSP realtime programming environment.