81 lines
2.4 KiB
Markdown
81 lines
2.4 KiB
Markdown
# Signalsmith Stretch: C++ pitch/time library
|
|
|
|
This is a C++11 library for pitch and time stretching, using the final approach from the ADC22 presentation _Four Ways To Write A Pitch-Shifter_.
|
|
|
|
It can handle a wide-range of pitch-shifts (multiple octaves) but time-stretching sounds best for more modest changes (between 0.75x and 1.5x). There are some audio examples on the [main project page](https://signalsmith-audio.co.uk/code/stretch/).
|
|
|
|
## How to use it
|
|
|
|
```cpp
|
|
#include "signalsmith-stretch.h"
|
|
|
|
signalsmith::stretch::SignalsmithStretch<float> stretch;
|
|
```
|
|
|
|
### Configuring
|
|
|
|
The easiest way to configure is a `.preset???()` method:
|
|
|
|
```cpp
|
|
stretch.presetDefault(channels, sampleRate);
|
|
stretch.presetCheaper(channels, sampleRate);
|
|
```
|
|
|
|
If you want to test out different block-sizes etc. then you can use `.configure()` manually.
|
|
|
|
### Processing (and resetting)
|
|
|
|
```cpp
|
|
// Clears internal buffers
|
|
stretch.reset();
|
|
|
|
float **inputBuffers, **outputBuffers;
|
|
int inputSamples, outputSamples;
|
|
stretch.process(inputBuffers, inputSamples, outputBuffers, outputSamples);
|
|
|
|
// Inspect latency
|
|
int totalLatency = stretch.inputLatency() + stretch.outputLatency();
|
|
```
|
|
|
|
The `.process()` method takes anything where `buffer[channel][index]` gives you a sample. This could be a `float **` or a `double **` or some custom object.
|
|
|
|
To get a time-stretch, just hand it differently-sized input/output buffers.
|
|
|
|
### Pitch-shifting
|
|
|
|
```cpp
|
|
stretch.setTransposeFactor(2); // up one octave
|
|
|
|
stretch.setTransposeSemitones(12); // also one octave
|
|
```
|
|
|
|
You can set a "tonality limit", which uses a non-linear frequency map to preserve a bit more of the timbre:
|
|
|
|
```cpp
|
|
stretch.setTransposeSemitones(4, 8000/sampleRate);
|
|
```
|
|
|
|
Alternatively, you can set a custom frequency map, mapping input frequencies to output frequencies (both normalised against the sample-rate):
|
|
|
|
```cpp
|
|
stretch.setFreqMap([](float inputFreq) {
|
|
return inputFreq*2; // up one octave
|
|
});
|
|
```
|
|
|
|
## Compiling
|
|
|
|
Just include `signalsmith-stretch.h` in your build.
|
|
|
|
It's pretty slow if optimisation is disabled though, so you might want to enable optimisation just where it's used.
|
|
|
|
### DSP Library
|
|
|
|
This uses the Signalsmith DSP library for FFTs and other bits and bobs.
|
|
|
|
For convenience, a copy of the license is included (with its own `LICENSE.txt`) in `dsp/`, but if you're already using this elsewhere then you should remove this copy to avoid versioning issues.
|
|
|
|
## License
|
|
|
|
[MIT License](LICENSE.txt) for now - get in touch if you need anything else.
|