Pitch drift is a commonly known phenomenon among singers. It occurs in most a cappella groups. Reasons for the phenomenon are not known, despite that it is very common and unwanted. It is usually mistakenly argued that pitch drift depends on the singers skills. The objective of this thesis is to find the causes of pitch drift. We reviewed scientific publications related to the theme and analysed the changes in intonation on audio tracks, which we recorded in the context of this thesis. Tracks were analyzed with algorithms for pitch detection. We used an existing plug-in based on pYIN algorithm and our own modified implementation of algorithm based on autocorrelation. The analysis results have further confirmed the findings of some publications, saying that the intonation in the songs changes due to differences between the just intonation and the equal temperament. Changes occur when difference in tuning between two notes is negative. More such cases are there in the song, greater change in the intonation can occur.
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