README
¶
Nanowarp
An ongoing attempt to create a professional grade audio time stretching algorithm. Reference implementation is going to be in Go, and a possible (Fil-)C implementation will share this repo with a Go version.
Includes a modified version of github.com/youpy/go-wav (ISC license) with added 32-bit float WAV support export.
Current state: algorithm mostly ready. No user-facing API exists yet.
Installation and usage
- Install Go
- Open terminal/shell/command prompt.
- Install Nanowarp
go install github.com/neputevshina/nanowarp/cmd/nanowarp@latest
- Use it
nanowarp -i inputfile.wav -t <stretch> [-o outputfile.wav]
or
nanowarp -i inputfile.wav -from <bpm> -to <bpm> -st <semitones> [-o outputfile.wav]
If your system can't find nanowarp executable, you have probably changed PATH variable in your system.
Probably the simplest way to bring it back if you are under Windows is by reinstalling the Go.
On Linux, you should probably know what to do.
Consult
nanowarp -help
to get the list of available options.
Implementation
Nanowarp is a phase gradient heap integration (PGHI) phase vocoder[1] where partial derivatives of phase are obtained through time-frequency reassignment[2]. This way accurate phase-time advance can be obtained using only one windowed grain instead of two.
Like in original implementation of PGHI-PV, FFT is oversampled by factor of 2 with zero-padding. Stereo coherence is obtained through stretching mono and adding phase difference of respective side channels to it after stretching to get stereo signals back[4].
A phase ramp for the entire output signal is generated. Onsets are detected using rectified complex-domain novelty function[3]. If onset is detected, phase ramp will have a derivative of 1 in a region around detected onset. Starting points of these sample regions are scaled by the stretch size, and points between regions are linearly interpolated.
Then the large-grained (nfft=4096) PGHI phase vocoder is applied, using phase ramp for the input sample indexes. If the derivative of the signal is 1, samples are passed through to the output unmodified.
Demos
TODO
Beat-emphasis onset detection
Testing strategy
- Various impulse train signals
- LFO FM Sine
- Vocals under hard saturation
- Drum loops
- Full tracks: pop, electronica, acoustica, black metal
Known issues
- No pitch modification. Requires a good resampler library, e.g. r8brain. Either port it or use through cgo.
- No streaming support. All processing is in-memory with obvious RAM costs.
- Slow.
- Smaller dynamic range comparing to original audio. Related to phase accuracy.
- Phase interruption on transients sometimes results in a “chopped” sound.
References
- Průša, Z., & Holighaus, N. (2017). Phase vocoder done right.
- Flandrin, P. et al. (2002). Time-frequency reassignment: from principles to algorithms.
- Duxbury, C., Bello, J. P., Davies, M., & Sandler, M. (2003, September). Complex domain onset detection for musical signals. In Proc. Digital Audio Effects Workshop (DAFx) (Vol. 1, pp. 6-9). London: Queen Mary University.
- Altoè, A. (2012). A transient-preserving audio time-stretching algorithm and a real-time realization for a commercial music product.
Documentation
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Index ¶
Constants ¶
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Variables ¶
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Functions ¶
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Types ¶
type Options ¶
type Options struct {
// Use time-phase derivative differences from mono in stereo preservation
// instead of phase differences.
Diffadv bool
// Output scaled onsets only.
Onsets bool
// Scale the time between transients quadratically.
Riddim bool
// Don't perform transient separation, output raw PVDR with phase reset
// with arbitrary periodicity.
Raw bool
}
Source Files
Directories