resampler 0.1.0

A small FFT based audio resampling library
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# resampler


Resampler is a small, no dependency crate that is optimized for resampling audio data from one to the other sampling
rate. Optimized for the most common audio sampling rates.

## Usage Example


```rust
use resampler::{Resampler, SampleRate};

// Create a stereo resampler (2 channels) from 44.1 kHz to 48 kHz.
let mut resampler = Resampler::<2>::new(SampleRate::Hz44100, SampleRate::Hz48000);

// Get required buffer sizes (already includes all channels).
let input_size = resampler.chunk_size_input();
let output_size = resampler.chunk_size_output();

// Create input and output buffers (interleaved format: [L0, R0, L1, R1, ...]).
let input = vec![0.0f32; input_size];
let mut output = vec![0.0f32; output_size];

// Process audio.
match resampler.resample(&input, &mut output) {
    Ok(()) => println!("Resample successful"),
    Err(error) => eprintln!("Resampling error: {error:?}"),
}
```

## Implementation


The resampler uses an FFT-based overlap-add algorithm with Kaiser windowing for high-quality audio resampling.
Key technical details:

- Custom mixed-radix FFT with the standard Cooley-Tukey algorithm.
- SIMD optimizations: All butterflies have SSE, AVX, and ARM NEON implementations with compile time CPU feature
  detection.
- Real-valued FFT: Exploits conjugate symmetry for 2x performance.
- Kaiser window: Beta parameter of 10.0 provides excellent stopband attenuation of -100 dB while maintaining good
  time-domain localization.
- Optimal configurations: Pre-computed FFT sizes and factorizations for all supported sample rate pairs, with throughput
  scaling to ensure a latency around 256 samples.

## Performance


SSE on x86_64 and NEON on aarch64 are enabled by default. But to get the best performance on x86_64 AVX (+avx) and FMA
(+fma) should be enabled at compile time as a target feature.

## Quality Analysis


The following spectrograms demonstrate the high-quality output of the resampler across different conversion scenarios:

### 44.1 kHz → 48 kHz Conversion


<img src="assets/analysis_44100_to_48000.png" width="100%" alt="Analysis of 44.1 kHz to 48 kHz resampling">

### 22.05 kHz → 44.1 kHz Conversion


<img src="assets/analysis_22050_to_44100.png" width="100%" alt="Analysis of 22.05 kHz to 44.1 kHz resampling">

## License


Licensed under either of

- Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

## Contribution


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as
defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.