Attention is drawn to the need for controlling (during encoding) and checking (after encoding) the quality or accuracy of musical data. Some large databases of melodies are now becoming available, and methods of control and checking are presented which are specially suited to these. Two applications are discussed in detail: to Gregorian Chant and to German folksong. An effective method in tonal and modal music is found to be the investigation of melodic progressions which remain unusual even after amalgamation by transposition to a central register.