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extern crate dft;
#[derive(Clone, Debug)]
pub struct FrequencyBucket {
pub min_freq: f64,
pub max_freq: f64,
pub intensity: f64
}
pub fn fft(input: Vec<f64>, sample_rate: f64) -> Vec<FrequencyBucket> {
let frames = input.len();
let plan = dft::Plan::new(dft::Operation::Forward, frames);
let mut intensities = input.clone();
dft::transform(&mut intensities, &plan);
let frequency_resolution = sample_rate / 2.0 / frames as f64;
intensities.iter().enumerate().map(|(index, &value)| {
let index = index as f64;
FrequencyBucket {
min_freq: index * frequency_resolution,
max_freq: (index+1.0) * frequency_resolution,
intensity: value
}
}).collect()
}
pub fn find_fundamental_frequency(frequency_domain: &Vec<FrequencyBucket>) -> Option<f64> {
//TODO look at all significant frequencies, find fundamental
//TODO return None is none of them are significant
let max_frequency = frequency_domain.iter()
.fold(None as Option<::transforms::FrequencyBucket>, |max, next|
if max.is_none() || max.clone().unwrap().intensity < next.intensity { Some(next.clone()) } else { max }
).unwrap().max_freq;
Some(max_frequency)
}
#[test]
fn fft_on_sine_wave() {
use std::f64::consts;
let sample_rate = 44100.0 as f64;
let amplitude = 1.0 as f64;
let frames = 16384;
let frequency = 10000.0 as f64; //10KHz
let frequency_resolution = sample_rate / 2.0 / frames as f64;
let samples = (0..frames)
.map(|x| {
let t = x as f64 / sample_rate;
(2.0 as f64 * consts::PI * frequency * t).sin() * amplitude
}).collect();
let result = fft(samples, sample_rate);
let fundamental = find_fundamental_frequency(&result);
assert!((fundamental-frequency).abs() < frequency_resolution, "expected={}, actual={}", frequency, fundamental);
}
pub fn hz_to_pitch(hz: f64) -> String {
let pitch_names = [
"C",
"C#",
"D",
"Eb",
"E",
"F",
"F#",
"G",
"G#",
"A",
"Bb",
"B"
];
let midi_number = 69.0 + 12.0 * (hz / 440.0).log2();
//midi_number of 0 is C-1.
let rounded_pitch = midi_number.round() as usize;
let name = pitch_names[rounded_pitch%pitch_names.len()].to_string();
let octave = rounded_pitch / pitch_names.len() - 1; //0 is C-1
let mut cents = ((midi_number * 100.0).round() % 100.0) as i32;
if cents >= 50 {
cents -= 100;
}
format!("{}{} {:+}", name, octave, cents)
}
#[test]
fn a4_is_correct() {
assert_eq!(hz_to_pitch(440.0), "A4 +0");
}
#[test]
fn a2_is_correct() {
assert_eq!(hz_to_pitch(110.0), "A2 +0");
}
#[test]
fn c4_is_correct() {
assert_eq!(hz_to_pitch(261.63), "C4 +0");
}
#[test]
fn f5_is_correct() {
assert_eq!(hz_to_pitch(698.46), "F5 +0");
}
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