This is a phase vocoder implementation written in Python. It can be used to time-stretch audio files. This program also implements independent pitch-shifting of audio in the frequency domain, with optional formant correction.
In order to use the main pvc.py script you must install the numpy, scipy, and SoundFile modules.
To use the JACK application you must also install tkinter and JACK-Client.
Run the following command to view the available parameters:
python3 pvc.py --help
A basic JACK client is also implemented that can perform pitch shifting of audio in real time. It can be started using the following command:
python3 pvc_jack.py
You'll then need to connect the inputs and outputs up using QJackCtl (or an equivalent program) as with any other JACK application. To use the program under PipeWire, add pw-jack at the beginning of the above command (on Debian, you may need to install the pipewire-audio-client-libraries package).
Currently, this phase vocoder can create significant phase artifacts when pitch-shifting audio at non-integer factors due to loss of vertical phase coherence (the different frequencies drift out of phase with respect to one another, causing a smearing effect). A few alternate algorithms are provided that may be able to reduce this problem but so far I have not found a complete solution.
Bernsee, Stephan M. "On the Importance of Formants in Pitch Shifting." Stephan Bernsee's Blog, 6 Feb. 2000, blogs.zynaptiq.com/bernsee/formants-pitch-shifting/.
Bernsee, Stephan M. "Pitch Shifting Using The Fourier Transform." Stephan Bernsee's Blog, 21 Sep. 1999, blogs.zynaptiq.com/bernsee/pitch-shifting-using-the-ft/.
De Götzen, Amalia, et al. "Traditional (?) Implementations of a Phase-Vocoder: The Tricks of the Trade." Proceedings of the COST G-6 Conference on Digital Audio Effects, 7-9 Dec. 2000.
Driedger, Johnathan, and Meinard Müller. "A Review of Time-Scale Modification of Music Signals." Applied Sciences, 18 Feb. 2016, vol. 6, no. 2, p. 57, www.mdpi.com/2076-3417/6/2/57.
Dudas, Richard, and Cort Lippe. "The Phase Vocoder - Part I." Cycling '74, 2 Nov. 2006, cycling74.com/tutorials/the-phase-vocoder-%E2%80%93-part-i.
Ellis, Dan. "A Phase Vocoder in Matlab." Dan Ellis's Home Page, 2002, www.ee.columbia.edu/~dpwe/resources/matlab/pvoc/.
Laroche, Jean, and Mark Dolson. "Phase-Vocoder: About this phasiness business." ResearchGate, Nov. 1997, www.researchgate.net/publication/3714372_Phase-vocoder_about_this_phasiness_business.
Sethares, William A. "A Phase Vocoder in Matlab." sethares homepage, sethares.engr.wisc.edu/vocoders/phasevocoder.html.