pvoc 0.1.1

A phase vocoder for making audio effects
Documentation 
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extern crate rustfft;
extern crate num;

use std::f64::consts::PI;
use std::collections::VecDeque;
use num::{Float, Complex, FromPrimitive, ToPrimitive};

#[allow(non_camel_case_types)]
type c64 = Complex<f64>;

/// Represents a component of the spectrum, composed of a frequency and amplitude.
#[derive(Copy, Clone)]
pub struct Bin {
    pub freq: f64,
    pub amp: f64,
}

impl Bin {
    pub fn new(freq: f64, amp: f64) -> Bin {
        Bin {
            freq: freq,
            amp: amp,
        }
    }
}

/// source: http://blogs.zynaptiq.com/bernsee/pitch-shifting-using-the-ft/
pub struct PhaseVocoder {
    channels: usize,
    sample_rate: f64,
    frame_size: usize,
    time_res: usize,

    samples_waiting: usize,
    in_buf: Vec<VecDeque<f64>>,
    out_buf: Vec<VecDeque<f64>>,
    last_phase: Vec<Vec<f64>>,
    sum_phase: Vec<Vec<f64>>,
    output_accum: Vec<VecDeque<f64>>,

    forward_fft: rustfft::FFT<f64>,
    backward_fft: rustfft::FFT<f64>,
}

impl PhaseVocoder {
    /// Constructs a new phase vocoder.
    ///
    /// channels: number of channels of audio
    /// sample_rate: it's the sample rate
    /// frame_size: fourier transform size
    /// time_res: number of frames to overlap
    pub fn new(channels: usize,
               sample_rate: f64,
               frame_size: usize,
               time_res: usize)
               -> PhaseVocoder {
        PhaseVocoder {
            channels: channels,
            sample_rate: sample_rate,
            frame_size: frame_size,
            time_res: time_res,

            samples_waiting: 0,
            in_buf: vec![VecDeque::new(); channels],
            out_buf: vec![VecDeque::new(); channels],
            last_phase: vec![vec![0.0; frame_size]; channels],
            sum_phase: vec![vec![0.0; frame_size]; channels],
            output_accum: vec![VecDeque::new(); channels],

            forward_fft: rustfft::FFT::new(frame_size, false),
            backward_fft: rustfft::FFT::new(frame_size, true),
        }
    }

    /// Read samples from input into queue, processs, then fill as much of output as possible.
    /// `processor` is a function to manipulate the spectrum before it is resynthesized. It's called
    /// like: `processor(num_channels, num_bins, &analysis_output, &mut synthesis_input)`
    /// Samples are expected to be normalized to the range [-1, 1].
    pub fn process<S, F>(&mut self, input: &[&[S]], output: &mut [&mut [S]], processor: F)
        where S: Float + ToPrimitive + FromPrimitive,
              F: Fn(usize, usize, &[Vec<Bin>], &mut [Vec<Bin>])
    {
        assert_eq!(input.len(), self.channels);
        assert_eq!(output.len(), self.channels);

        // push samples to input queue
        for chan in 0..input.len() {
            for samp in 0..input[chan].len() {
                self.in_buf[chan].push_back(input[chan][samp].to_f64().unwrap());
                self.samples_waiting += 1;
            }
        }
        while self.samples_waiting >= 2 * self.frame_size * self.channels {
            let frame_size = self.frame_size;
            let step_size = frame_size / self.time_res;
            let expect = 2.0 * PI * (step_size as f64) / (frame_size as f64);
            let freq_per_bin = self.sample_rate / (frame_size as f64);

            for _ in 0..self.time_res {
                let mut analysis_out = vec![vec![Bin::new(0.0, 0.0); frame_size]; self.channels];
                let mut synthesis_in = vec![vec![Bin::new(0.0, 0.0); frame_size]; self.channels];

                // ANALYSIS
                for chan in 0..self.channels {
                    let samples = &self.in_buf[chan];
                    let mut last_phase = &mut self.last_phase[chan];
                    let mut fft_in = vec![c64::new(0.0, 0.0); frame_size];
                    let mut fft_out = vec![c64::new(0.0, 0.0); frame_size];

                    // read in
                    for i in 0..frame_size {
                        let window = window((i as f64) / (frame_size as f64));
                        fft_in[i] = c64::new(samples[i] * window, 0.0);
                    }

                    self.forward_fft.process(&fft_in, &mut fft_out);

                    for i in 0..frame_size {
                        let x = fft_out[i];

                        let (amp, phase) = x.to_polar();

                        // convert phase to frequency
                        let mut tmp = phase - last_phase[i];
                        last_phase[i] = phase;
                        tmp -= (i as f64) * expect;
                        let mut qpd = (tmp / PI) as i32;
                        if qpd >= 0 {
                            qpd += qpd & 1;
                        } else {
                            qpd -= qpd & 1;
                        }
                        tmp -= PI * (qpd as f64);
                        tmp = (self.time_res as f64) * tmp / (2.0 * PI);
                        tmp = (i as f64) * freq_per_bin + tmp * freq_per_bin;

                        analysis_out[chan][i] = Bin::new(tmp, amp * 2.0);
                    }
                }

                // PROCESSING
                processor(self.channels, frame_size, &analysis_out, &mut synthesis_in);

                // SYNTHESIS
                for chan in 0..self.channels {
                    let mut sum_phase = &mut self.sum_phase[chan];
                    let mut fft_in = vec![c64::new(0.0, 0.0); frame_size];
                    let mut fft_out = vec![c64::new(0.0, 0.0); frame_size];
                    for i in 0..frame_size {
                        let amp = synthesis_in[chan][i].amp;
                        let mut tmp = synthesis_in[chan][i].freq;

                        // convert frequency to phase
                        tmp -= (i as f64) * freq_per_bin;
                        tmp /= freq_per_bin;
                        tmp = 2.0 * PI * tmp / (self.time_res as f64);
                        tmp += (i as f64) * expect;
                        sum_phase[i] += tmp;
                        let phase = sum_phase[i];

                        fft_in[i] = c64::from_polar(&amp, &phase);
                    }

                    self.backward_fft.process(&fft_in, &mut fft_out);

                    // accumulate
                    for i in 0..frame_size {
                        let window = window((i as f64) / (frame_size as f64));
                        if i == self.output_accum[chan].len() {
                            self.output_accum[chan].push_back(0.0);
                        }
                        self.output_accum[chan][i] += window * fft_out[i].re /
                                                      ((frame_size as f64) *
                                                       (self.time_res as f64));
                    }

                    // write out
                    for _ in 0..step_size {
                        self.out_buf[chan].push_back(self.output_accum[chan].pop_front().unwrap());
                        self.in_buf[chan].pop_front();
                    }
                }
            }
            self.samples_waiting -= self.frame_size * self.channels;
        }

        // pop samples from output queue
        for chan in 0..self.channels {
            for samp in 0..output[chan].len() {
                output[chan][samp] = match self.out_buf[chan].pop_front() {
                    Some(x) => FromPrimitive::from_f64(x).unwrap(),
                    None => break,
                }
            }
        }
    }
}

fn window(x: f64) -> f64 {
    -0.5 * (2.0 * PI * x).cos() + 0.5
}