The method usually used to identify different sounds or divisions of sounds is to compare sonograms visually. There have been some attempts to reduce the subjectivity and increase the repeatability of this approach, for example by tracing the sonograms onto paper and examining the areas of overlap and mismatch, the use of multi-variate statistics and digitizing tablets. Digital recording of sounds has allowed sounds to be input directly into computers which can be used to display sounds and facilitate measurement. To date there has been little attempt at their use or analysis. We outline a series of programs which have been developed to compare statistically any unit of a sound with a pre-recorded library of similar units. The creation of such a library allows the rapid and objective categorization of large numbers of sounds. These programs have been used to analyse songs recorded from wrens Troglodytes troglodytes and house crickets Acheta domesticus. Potential applications of this software to the field of bioacoustic investigation are discussed.