rubato

An audio sample rate conversion library for Rust.

This library provides resamplers to process audio in chunks.

The ratio between input and output sample rates is completely free. Implementations are available that accept a fixed length input while returning a variable length output, and vice versa.

Rubato can be used in realtime applications without any allocation during processing by preallocating a [Resampler] and using its input_buffer_allocate and output_buffer_allocate methods before beginning processing. The log feature feature should be disabled for realtime use (it is disabled by default).

Input and output data format

Input and output data is stored non-interleaved.

Input and output data are stored as slices of references, &[AsRef<[f32]>] or &[AsRef<[f64]>]. The inner vectors (AsRef<[f32]> or AsRef<[f64]>) hold the sample values for one channel each.

Since normal vectors implement the AsRef trait, Vec<Vec<f32>> and Vec<Vec<f64>> can be used for both input and output.

Asynchronous resampling

The asynchronous resamplers are available with and without anti-aliasing filters.

Resampling with anti-aliasing is based on band-limited interpolation using sinc interpolation filters. The sinc interpolation upsamples by an adjustable factor, and then the new sample points are calculated by interpolating between these points. The resampling ratio can be updated at any time.

Resampling without anti-aliasing omits the cpu-heavy sinc interpolation. This runs much faster but produces a lower quality result.

Synchronous resampling

Synchronous resampling is implemented via FFT. The data is FFT:ed, the spectrum modified, and then inverse FFT:ed to get the resampled data. This type of resampler is considerably faster but doesn't support changing the resampling ratio.

SIMD acceleration

Asynchronous resampling with anti-aliasing

The asynchronous resampler supports SIMD on x86_64 and on aarch64. The SIMD capabilities of the CPU are determined at runtime. If no supported SIMD instruction set is available, it falls back to a scalar implementation.

On x86_64 it will try to use AVX. If AVX isn't available, it will instead try SSE3.

On aarch64 (64-bit Arm) it will use Neon if available.

Synchronous resampling

The synchronous resamplers benefit from the SIMD support of the RustFFT library.

Cargo features

fft_resampler: Enable the FFT based synchronous resamplers

This feature is enabled by default. Disable it if the FFT resamplers are not needed, to save compile time and reduce the resulting binary size.

log: Enable logging

This feature enables logging via the log crate. This is intended for debugging purposes. Note that outputting logs allocates a std::string::String and most logging implementations involve various other system calls. These calls may take some (unpredictable) time to return, during which the application is blocked. This means that logging should be avoided if using this library in a realtime application.

Example

Resample a single chunk of a dummy audio file from 44100 to 48000 Hz. See also the "process_f64" example that can be used to process a file from disk.

use rubato::{Resampler, SincFixedIn, SincInterpolationType, SincInterpolationParameters, WindowFunction};
let params = SincInterpolationParameters {
    sinc_len: 256,
    f_cutoff: 0.95,
    interpolation: SincInterpolationType::Linear,
    oversampling_factor: 256,
    window: WindowFunction::BlackmanHarris2,
};
let mut resampler = SincFixedIn::<f64>::new(
    48000 as f64 / 44100 as f64,
    2.0,
    params,
    1024,
    2,
).unwrap();

let waves_in = vec![vec![0.0f64; 1024];2];
let waves_out = resampler.process(&waves_in, None).unwrap();

Included examples

The examples directory contains a few sample applications for testing the resamplers. There are also Python scripts for generating simple test signals, as well as analyzing the resampled results.

The examples read and write raw audio data in 64-bit float format. They can be used to process .wav files if the files are first converted to the right format. Use sox to convert a .wav to raw samples:

sox some_file.wav -e floating-point -b 64 some_file_f64.raw

After processing, the result can be converted back to new .wav. This examples converts to 16-bits at 44.1 kHz:

sox -e floating-point -b 64 -r 44100 -c 2 resampler_output.raw -e signed-integer -b 16 some_file_resampled.wav

Many audio editors, for example Audacity, are also able to directly import and export the raw samples.

Compatibility

The rubato crate requires rustc version 1.61 or newer.

Changelog

• v0.15.0
  • Make FFT resamplers optional via fft_resampler feature.
  • Fix calculation of input and output sizes when creating FftFixedInOut resampler.
  • Fix panic when using very small chunksizes (less than 5).
• v0.14.1
  • More bugfixes for buffer allocation and max output length calculation.
  • Fix building with log feature.
• v0.14.0
  • Add argument to let input/output_buffer_allocate() optionally pre-fill buffers with zeros.
  • Add convenience methods for managing buffers.
  • Bugfixes for buffer allocation and max output length calculation.
• v0.13.0
  • Switch to slices of references for input and output data.
  • Add faster (lower quality) asynchronous resamplers.
  • Add a macro to help implement custom object safe resamplers.
  • Optional smooth ramping of ratio changes to avoid audible steps.
  • Add convenience methods for handling last frames in a stream.
  • Add resampler reset method.
  • Refactoring for a more logical structure.
  • Add helper function for calculating cutoff frequency.
  • Add quadratic interpolation for sinc resampler.
  • Add method to get the delay through a resampler as a number of output frames.
• v0.12.0
  • Always enable all simd acceleration (and remove the simd Cargo features).
• v0.11.0
  • New api to allow use in realtime applications.
  • Configurable adjust range of asynchronous resamplers.
• v0.10.1
  • Fix compiling with neon feature after changes in latest nightly.
• v0.10.0
  • Add an object-safe wrapper trait for Resampler.
• v0.9.0
  • Accept any AsRef<[T]> as input.

License: MIT