The sounds of each piano are picked up by microphones and fed into an apparatus at the player's left side. This is called a Modul 69 B and was specially built for "Mantra" to the composer's specification by the Lawo company from Rastatt, near Baden-Baden. It consists of a microphone amplifier with three microphone inputs, a compressor, a filter, a ring modulator, a scaled sine-wave generator, and a volume control. By means of this device, each piano's sounds are ring modulated with a sine tone tuned to the central pitch corresponding to the note of the mantra formula governing each of the thirteen large segments of the composition, and the modulated sound is played over loudspeakers placed behind and above the performers. The first pianist presents the upper thirteen tones, the second pianist the lower thirteen tones. Because the starting/ending pitch of the mantra is successively transposed onto these central pitches, they sound completely "consonant", like ordinary piano tones. The other mantra pitches sound "dissonant" to varying degrees, and differ also from a normal piano to varying degrees in their timbre. "Hence one perceives a continual 'respiration' from consonant to dissonant to consonant modulator sounds, resulting from the precisely tuned relationships between the modulating sine tones and the modulated piano notes".