In this paper we investigate how various feature sets influence precision, recall, and accuracy of identification of multiple instruments in polyphonic recordings. Our investigations were performed on classical music, and musical instruments typical for this music. Five feature sets were investigated. The results show that precision and recall change to a great extend, beyond the usual trade-off, whereas accuracy is relatively stable. Also, the results depend on the polyphony level of particular pieces of music. The investigated music varies in polyphony level, from 2-instrument duet (with piano) to symphonies.