It’s Just a Phase: Exploring Synthesis With the Phase Vocoder
Can we do time-stretching…in real-time? What if instead of just stretching time, we could freeze it, scrub through it, and morph between different moments in a sound?
We will explore this question, and more, by trying to build out some creative ideas for synthesis armed with just a few samples and the trusty FFT.
We will cover the basics of time-stretching audio using the FFT with phase-vocoding, and in doing so try to build an intuition of how phases in a Fourier Transform affect the sound with some beautiful interactive plots.
We'll then try to build out a full synth using some of these (usually offline) time-stretching techniques - a waveform player where you can scrub over the sound at any speed, use a playhead to pause, freezing the sound, then randomly move around. We will introduce some pitch shifting, and show that phase-vocoding offers a texturally rich and organic alternative to granular synthesis - no grain boundaries or windowing artifacts.
Through the whole talk I'll try to answer questions like:
- What the heck even ARE phases?
- How do we handle phase coherence differently for onsets versus harmonic sounds?
- How do we make processed noise sound natural instead of artificial?
- How can we use these algorithms in real-time synthesis?
Throughout, we'll dig into practical implementation details - you'll come away with some tools for using FFTs in ways you might not have expected, and techniques for making these algorithms work in real-time. I’ll also provide a link to an open-source library that uses these techniques.
Target Audience: Audio developers with basic FFT knowledge interested in creative synthesis applications and practical DSP implementation.
Cameron Thomas
Founder
Minuit
Hi, I'm Cam.
I run Minuit, a small indie plugin company where I'm currently releasing (or just released, hopefully) Solstice - an experimental synthesiser based on the phase-vocoding techniques I'll be talking about today.
Previously, I spent six years as a Staff Software Engineer at Vochlea Music, developing the Dubler voice-to-MIDI applications. These days I've gone indie to explore more experimental sound design ideas, whilst also taking on contract plugin development.
I'm particularly interested in making complex DSP feel intuitive and playable. As someone who makes experimental and ambient music in my spare time, I enjoy finding new ways to process sound that go beyond traditional synthesis methods - which is exactly what led me down the phase-vocoder rabbit hole, after playing around with neural synthesis back in 2018/19 and finding it frustrating to work with.