The experimental Robotone audio effect plugin applies a fixed pitch onto a sound controlled by a MIDI note event. Originally this technique puts zero phase values on every STFT frame before reconstruction [1,2,3]. However, the phase zeroing effect is emulated in Robotone using the Sliding DFT as implemented in SDFT. This enables polyphonic usage in a single processing step.
The basic idea behind this effect is to reinterpret the frequency axis by replacing the DFT bin frequencies with overtone series as played on a MIDI keyboard. When applied to the vocal input, this particular modification produces a robotic sound at a fixed pitch. Additional phase vocoder based corrections result in pitch shifting. Unfortunately, the pitch shifted output does not preserve the formants. This issue might be resolved in a future version.
However both effect variants can be used to add a harmonic touch to vocals in a musical way. I suppose so at least...
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Vincent Verfaille, Daniel Arfib (2001). Adaptive Digital Audio Effects. https://dafx.de/paper-archive/2001/papers/verfaille_a.pdf
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Vincent Verfaille, Udo Zölzer, Daniel Arfib (2006). Adaptive Digital Audio Effects. https://hal.science/hal-00095922/document
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Udo Zölzer (2011). Digital Audio Effects. https://www.dafx.de/DAFX_Book_Page_2nd_edition/index.html
Robotone is licensed under the terms of the GPL license. For details please refer to the accompanying LICENSE file distributed with Robotone.