Ambient 2: The Plateaux of Mirror is a 1980 album by ambient musicians Harold Budd and Brian Eno. This is the second instalment of Eno's Ambient series which began in 1978 with Ambient 1: Music for Airports, identifiable by its similar cover art which looks like it depicts rural terrain on a map.
Eno said of Budd that he indulged in "live improvisation on The Plateaux of Mirror ... I would set up a sound, he would improvise to it, and occasionally I would add something: but it was mainly him performing in a sound-world I had created".
Speaking about how Budd discovered new ways of playing on the album simply by bouncing ideas off each other, Eno has also commented "... with him I used to set up quite complicated treatments and then he would go out and play the piano. And you would hear him discovering, as he played, how to manipulate this treatment. How to make it ring and resonate. Which notes work particularly well on it. Which register of the piano. What speed to play at, of course, because some treatments just cloud out if they have too much information in them".
The bulk of the instrumentation is Budd on acoustic piano with treatments by Eno. "The Plateaux of Mirror" and "Wind in Lonely Fences" are performed on electric piano. Budd composed "Not Yet Remembered" in California, with a melodic line intended for vocals, and mailed the composition to Eno in New York City. Eno then reversed the melodic phrase, recorded it and played it to Budd for the first time over the telephone. The basic theme of "The Chill Air" was repeated on "Their Memories," a piece on Budd and Eno's 1984 release The Pearl. While the theme is recognisable by its melody line, the treatments are more pronounced.
Tracks 2, 4, 7, 8 and 10 are mostly piano-oriented, with little in the way of heavy electronic tinkering by Eno; track 1, also piano-based, has some light synthesizer treatments towards the latter half. Tracks 3 and 9 feature syncopation, mostly in the form of light chimes, while track 6 has wordless vocal-style effects accompanying the piano. Track 5's piano is backed with some warm synthesizers, the most uptempo composition on the album.
Because the album was recorded on analogue equipment, the listener can hear the hiss of the tapes Eno used for his treated sounds in several of the tracks.