the riff for the jam song "Who Knows". The trio began rehearsing a set of songs for the four upcoming Fillmore shows. Many of these songs represent a change in Hendrix's music from his Experience repertoire. Biographer and later Hendrix producer John McDermott elaborates Most of the arrangements were developed through extensive jamming, with Cox's and Miles' playing influencing Hendrix's ideas. According to biographer Keith Shadwick, Cox explained in later interviews, "the process was based on building up rhythm patterns and that each pattern dictated the shape and character of a portion of a song in which it appeared". Record producer Alan Douglas witnessed the approach during a jam at the Record Plant and saw it as inefficient. On the other hand, Shadwick feels that it was necessary: "it seemed the only way available, especially as neither Cox nor Miles, in particular, were exactly swift on the musical uptake". Music journalist Charles Shaar Murray noted, "Cox's funky, uncluttered bass style would give Hendrix's new music a more solid, less frenetic underpinning [than Noel Redding's style]. In every way, Cox's function would be to provide the steadiness Hendrix so urgently required". Soft Machine drummer Robert Wyatt described Miles' style as "pleasantly messy ... He wasn't as tight as a Stax drummer [such as Al Jackson Jr. ] ... his rolls would clatter about a bit". However, his often described "fatback grooves" lay down a solid rhythmic foundation and the combination of Cox and Miles adds a "heavy, rolling fluidity which brings out a very different dimension in Hendrix's playing". The mix of improvisation and R&B/funk elements is evident in "Who Knows", which was the opening song for the second (after the brief "Auld Lang Syne") and third shows. It is a loose jam rather than a structured composition and during the performance for the second show Hendrix teases the audience with "I hope you don't mind us jamming a little bit, we're just messing around ... seeing what we're gonna play next". Built on Hendrix's guitar figure, "Who Knows" is framed by Cox's economical funk-blues bass line and Miles' steady drum beat, which Murray describes as "a thick, lazy twitch". Hendrix explores guitar phrases using different tones and effects between vocal sections. According to Cox, Hendrix used a new combination of effects for the first time. These included a Uni-Vibe phase shifter, an Octavia (developed for him by Roger Mayer during