Brady, P.T. (1970). Fixed-scale mechanism of absolute pitch. J. Acoust.  Soc.  Am. 48,  883-887

With intensive training, the author, who had no previous ability in identification of randomly presented tones from the 12-tone musical scale, achieved a performance level of 65% exactly correct and 97% correct within \pm 1 half-step (semitone). The training task consisted of spending many hours hearing an identifying randomly presented tones with feedback on the judgments. Successful acquisition of absolute-tone identifcation contributes to the evidence that an adult can learn this task, but apparently only with great effort. It is suggested that naturally occurring absolute pitch is not an innate ability. Rather, this skill results from perceiving only one musical scale (for example, C-major), and if music is played in a different scale, the notes retain their C-major perceptual values. This mechanism, which is probably acquired in early childhood, can account for much of the introspective and performance data from possessors and non-possessors of absolute pitch.