During the February 3, 1967, session at Olympic, the Experience improved the January 11 master tape of "Purple Haze" by re-recording the vocal and lead guitar parts, and adding another Octavia guitar overdub, which was sped-up and panned at the end of the song. The group reconvened at Olympic on February 7, continuing their work on "Purple Haze" by recording Hendrix's rhythm guitar and vocal parts, as well as Redding's background vocals. They spent time overdubbing ambient background sounds by playing tapes through a set of headphones that were held near a microphone, creating an echo effect as the headphones were moved closer; they completed a final mix of "Purple Haze" the following day. During the session, they worked on the De Lane Lea master tape of "Fire", replacing everything except Redding's bass line, which he double-tracked in an effort to accentuate the recording's lower frequencies. Kramer placed the second bass line on a dedicated track and blended Redding's original bass line with Mitchell's newly recorded drum part. They also recorded Mitchell and Redding's backing vocals. "Foxy Lady" was also reworked on February 8; Redding recorded a new bass line and Hendrix and Mitchell added overdubs to their existing parts. After recording backing vocals by Redding and lead vocals from Hendrix, Kramer prepared the song's final mix.