Rust: `no_std` digital low pass filter library

This is a no_std Rust library for simple digital low pass filters. You can use it for example to get the low frequencies from a song.

I'm not an expert on digital signal processing. Code contributions are highly welcome! :)

How to use

```rust use std::path::PathBuf; use std::fs::File; use audiovisualizer::waveform::staticc::pngfile::visualize; use audiovisualizer::{Channels, ChannelInterleavement}; use std::time::Instant; use lowpassfilter::simple::sp::applylpfi16_sp; use minimp3::{Decoder as Mp3Decoder, Frame as Mp3Frame, Error as Mp3Error};

fn main() { let mut path = PathBuf::new(); path.push("test/samples"); path.push("sample_1.mp3"); let mut decoder = Mp3Decoder::new(File::open(path).unwrap());

let mut lrlr_mp3_samples = vec![];
loop {
    match decoder.next_frame() {
        Ok(Mp3Frame { data: samples_of_frame, .. }) => {
            for sample in samples_of_frame {
                lrlr_mp3_samples.push(sample);
            }
        }
        Err(Mp3Error::Eof) => break,
        Err(e) => panic!("{:?}", e),
    }
}
// split into left and right channel
let (mut left, mut right) = Channels::Stereo(ChannelInterleavement::LRLR)
    .stereo_interleavement()
    .to_channel_data(&lrlr_mp3_samples);


// left: low pass filter with i16 samples in single precision
apply_lpf_i16_sp(&mut left, 44100, 120);
// right: lpf with i16 samples in single precision
apply_lpf_i16_sp(&mut right, 44100, 120);

// visualize audio as waveform in a PNG file
visualize(
    &left,
    Channels::Mono,
    "test/out",
    "sample_1_waveform_lowpassed_left.png"
);
visualize(
    &right,
    Channels::Mono,
    "test/out",
    "sample_1_waveform_lowpassed_right.png"
);

} ```