Pitch-shifting algorithm design and applications in music

Sammanfattning: Pitch-shifting lowers or increases the pitch of an audio recording. This technique hasbeen used in recording studios since the 1960s, many Beatles tracks being producedusing analog pitch-shifting effects. With the advent of the first digital pitch-shiftinghardware in the 1970s, this technique became essential in music production. Nowadays,it is massively used in popular music for pitch correction or other creative purposes.With the improvement of mixing and mastering processes, the recent focusin the audio industry has been placed on the high quality of pitch-shifting tools. Asa consequence, current state-of-the-art literature algorithms are often outperformedby the best commercial algorithms. Unfortunately, these commercial algorithms are”black boxes” which are very complicated to reverse engineer.In this master thesis, state-of-the-art pitch-shifting techniques found in the literatureare evaluated, attaching great importance to audio quality on musical signals.Time domain and frequency domain methods are studied and tested on a wide rangeof audio signals. Two offline implementations of the most promising algorithms areproposed with novel features. Pitch Synchronous Overlap and Add (PSOLA), a simpletime domain algorithm, is used to create pitch-shifting, formant-shifting, pitchcorrection and chorus effects on voice and monophonic signals. Phase vocoder, amore complex frequency domain algorithm, is combined with high quality spectralenvelope estimation and harmonic-percussive separation to design a polyvalentpitch-shifting and formant-shifting algorithm. Subjective evaluations indicate thatthe resulting quality is comparable to that of the commercial algorithms.