Due to the time limit, U2 were forced to write and record songs at a more rapid pace. They continued their long-time practice of jamming in the studio. Eno used an eraseable whiteboard to give instructions and cues to the band while they jammed; he pointed at chords and various commands, such as "hold", "stop", "change", and "change back", to direct their performances. Flood recorded the material, while Eno alternated between performing with U2 and joining Flood in the control room. At the end of a given week, Eno and Flood compared their notes and compiled the week's best jams onto a cassette for the band to listen to. The producers edited together their favourite sections of the jams and then discussed the arrangements with the group. U2 suggested alterations and added lyrics and melodies, before performing to the edited arrangements. To record all of the band's material and test different arrangements, the engineers utilised a technique they called "fatting", which allowed them to achieve more than 48 tracks of audio by using a 24-track analogue recording, a Fostex D20 timecode-capable DAT recorder, and an Adams Smith Zeta Three synchroniser; Adams went through 180 two-hour DAT tapes during the recording sessions. The production crew faced issues with audio spill at The Factory, as all group members recorded in the same room as the mixing desk and Bono frequently sang in-progress lyrics that would need to be replaced. Gobos and wood booths were built to separate the performers' sounds as much as possible.