Whereas the general population usually sings accurately (Dalla Bella 2007), certain individuals display a real deficit in pitch matching whilst singing. The description of this deficit in adults is in its infancy. This is an acoustic study of 15 adults judged socially as poor singers. The accuracy is tested by three elementary tests of song: A reproduction of isolated notes, a reproduction of sequences of notes, a song "a capella". A test of microphone-tonal discrimination was added and the fundamental frequency of the productions was analyzed. We showed that the deficits are heterogeneous: The control of pitch can be insufficient on the level of the tonal centre, the intervals between notes, and sometimes on the level of the note itself with regard to the target being aimed at. The error tends to be an undervaluation. The capacity for fine discrimination is however preserved for part of our study population. Broader studies of deviating productions should be undertaken looking at the diversity of deterioration and the specificity of the tasks as they could shed a new light on the cognitive processes which control the installation of the vocal control.