The number of unique instruments for each track average to about a dozen. Electric and acoustic basses were frequently doubled, as was typical for the era's pop music, and played with a plectrum. Drums were not arranged in a traditional manner of keeping time, but instead, to provide "rhythmic texture and color". Two tracks are instrumentals: "Let's Go Away for Awhile" and "Pet Sounds". They were originally recorded as backing tracks for existing songs, but by the time the album neared completion, Wilson decided that the tracks worked better without vocals. Arranger Paul Mertens, who collaborated with Wilson on live performances of the album, believed that although there are string sections on "Pet Sounds", "what's special about that is not that Brian was trying to introduce classical music into rock & roll. Rather, he was trying to get classical musicians to play like rock musicians. He's using these things to make music in the way that he understood, rather than trying to appropriate the orchestra." Wilson tended to write vertically, in block chords, rather than in the horizontal manner of classical composition.