in the Columbia–Princeton Electronic Music Center in New York City, the first of its kind in the United States. After Ussachevsky suggested to Carlos that she work in a recording studio to support herself, Carlos began working as a recording and mastering engineer at Gotham Recording Studios in New York City; she worked in this position until 1968. She called it "a really lovely occupation" and found it a useful learning experience. During her time at Columbia, Carlos met Robert Moog at the 1964 Audio Engineering Society show, which began a partnership. Carlos ordered custom-designed synthesizer modules from Moog, and gave him extensive advice and technical assistance in the development of what became the Moog synthesizer, Moog's new electronic instrument. She convinced Moog to add a touch-sensitive keyboard for greater musical dynamics, among other improvements. Moog recounted that Carlos fed back extensive and very detailed -- but always constructive -- criticism about his equipment, presenting him with suggestions for improvements to every module, including the shapes and dimensions of the cases. Moog credited Carlos with originating many features of his synthesizer, and that many features that became part of the final production model of the Moog synthesizer originated with the custom modules he created for her, including the touch-sensitive keyboard, a portamento control, a fixed filter bank, and a 49-oscillator polyphonic generator bank that could create chords and arpeggios. By 1966 Carlos owned a small Moog synthesizer, which she used to record sound effects and jingles for television commercials, which earned her "anywhere from $100 to $1000.” In 1967, Carlos met and befriended fellow Gotham Recorders employee Rachel Elkind, a former singer who had a jazz and musical theatre background and had worked as a secretary for Goddard Lieberson, then-president of Columbia Records. Although their initial meetings were somewhat confrontational (Elkind initally found Carlos "arrogant"), they eventually became friends and began sharing a home, studio, and business premises in a brownstone building in the West Side of Manhattan in New York City. Carlos recorded several compositions in the 1960s as a student at the Columbia-Princeton Electronic Music Center. Two of them were re-recorded and released on By Request (1975), Dialogues for Piano and Two Loudspeakers (1963) and Episodes for Piano and Electronic Sound (1964), both featuring Phillip Ramey on piano. A third, Variations for Flute and Electronic Sounds (1964, featuring John Heiss on flute) was recorded and released in 1965