team realised that the ballroom had too much natural reverberation, necessitating the addition of sound absorption materials such as drapes to the walls. Lanois said the room was only suitable for songs with "openness but not good for tracks that were quick and required punch", while crew member Stephen Rainford said, "Okay for chamber music, but no good for rock and roll". Consequently, most of the recording took place in the library, which was smaller, rectangular, filled with books, and provided improved sound quality. Lanois said the room helped them "achieve a denser more powerful sound" on their recordings. Adding to the recording challenges was the water wheel generator on River Boyne that powered the building. During low tide or periods of no rain, there was not sufficient power to keep their recording equipment operational. Ezratty said, "When that stupid river started to run low, the voltage would go down and it would beat the crap out of my equipment." As a backup, the team were forced to make use of an old diesel generator, which at times broke down or caught fire. The Edge was encouraged by Eno to think of the studio as an instrument and to expand the range of his guitar tones, resulting in experiments with his equipment and guitar playing techniques. The producer processed the Edge's guitar through an AMS harmonizer effects unit, a Lexicon Prime Time delay unit, and a reverb chamber; Lanois at times confused the guitar sounds for keyboards. The Edge also used an EBow, a slide with echo, alternative guitar tunings, and a "zero sustain" technique that muted his strings with tape across the bridge. He experimented with the placement and miking of his guitar amplifier. At times, it was situated outside on the balcony encircling the castle, with close miking and, when it rained, a plastic cover to shield it.Graham (1996), pp. 22–23 This placement was originally done for sound isolation purposes, but ended up producing a good sound. Other times, his amplifier was placed at the bottom of a staircase, with one microphone there and another placed at the top of the staircase. A Fairlight CMI synthesiser was used during the demoing phase out of convenience to help fill in placeholder textures and string ideas, marking the first time the instrument had been used on a U2 album. These textures were later replaced with actual string arrangements, although the