Beatle". He applied his classical musical training in various ways, and functioned as "an informal music teacher" to the progressing songwriters, according to Gould. Martin suggested to a sceptical McCartney that the arrangement of "Yesterday" should feature a string quartet accompaniment, thereby introducing the Beatles to a "hitherto unsuspected world of classical instrumental colour", in MacDonald's description. Their creative development was also facilitated by Martin's willingness to experiment in response to their suggestions, such as adding "something baroque" to a particular recording. In addition to scoring orchestral arrangements for recordings, Martin often performed on them, playing instruments including piano, organ and brass. Collaborating with Lennon and McCartney required Martin to adapt to their different approaches to songwriting and recording. MacDonald comments, "while [he] worked more naturally with the conventionally articulate McCartney, the challenge of catering to Lennon's intuitive approach generally spurred him to his more original arrangements, of which "Being for the Benefit of Mr. Kite!" is an outstanding example." Martin said of the two composers' distinct songwriting styles and his stabilising influence: Harrison echoed Martin's description of his stabilising role: "I think we just grew through those years together, him as the straight man and us as the loonies; but he was always there for us to interpret our madness – we used to be slightly avant-garde on certain days of the week, and he would be there as the anchor person, to communicate that through the engineers and on to the tape." In the studio Making innovative use of technology while expanding the possibilities of recorded music, the Beatles urged experimentation by Martin and his recording engineers. Seeking ways to put chance occurrences to creative use, accidental guitar feedback, a resonating glass bottle, a tape loaded the wrong way round so that it played backwards – any of these might be incorporated into their music. Their desire to create new sounds on every new recording, combined with Martin's arranging abilities and the studio expertise of EMI staff engineers Norman Smith, Ken Townsend and Geoff Emerick, all contributed significantly to their records from Rubber Soul and, especially, Revolver onwards. Along with innovative studio techniques such as sound effects, unconventional microphone placements, tape loops, double tracking and vari-speed recording, the Beatles augmented their songs with instruments that were unconventional in rock music at the time. These included string and brass ensembles as well as Indian instruments such as the sitar