FM via https://github.com/haruki7049/lightmix

fm.zig

const std = @import("std");
const lightmix = @import("lightmix");

const T = f64;
const SAMPLE_RATE: u32 = 44100;
const CHANNELS: u16 = 1;
const LENGTH: usize = SAMPLE_RATE * 2;
const FREQUENCY: T = 440.0;
const VOLUME: T = 0.5;

pub fn gen(allocator: std.mem.Allocator) !lightmix.Wave(T) {
    var samples = try allocator.alloc(T, LENGTH);

    for (0..samples.len) |i| {
        // Modulator
        const radians_per_sec_mod: T = FREQUENCY * 10.0 * std.math.pi;
        const mod: T = std.math.sin(
            @as(T, @floatFromInt(i)) * radians_per_sec_mod / @as(T, @floatFromInt(SAMPLE_RATE)),
        );

        // Modulation index
        const mod_idx: T = 1.0;

        // Carrier
        const radians_per_sec_car: T = FREQUENCY * 3.33 * std.math.pi;
        const car: T = std.math.sin(
            @as(T, @floatFromInt(i)) * radians_per_sec_car / @as(T, @floatFromInt(SAMPLE_RATE)) + (mod * mod_idx),
        );

        // Carrier index
        const car_idx: T = VOLUME;

        // result
        const result: T = car * car_idx;

        samples[i] = result;
    }

    return lightmix.Wave(T){
        .allocator = allocator,
        .samples = samples,
        .sample_rate = SAMPLE_RATE,
        .channels = CHANNELS,
    };
}