sfxr.lua/sfxr.lua

-- sfxr.lua
-- original by Tomas Pettersson, ported to Lua by nucular

--[[
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
]]--

local sfxr = {}
local bit = bit32 or require("bit")

-- Constants

sfxr.VERSION = "0.0.1"

sfxr.SQUARE = 0
sfxr.SAWTOOTH = 1
sfxr.SINE = 2
sfxr.NOISE = 3

sfxr.FREQ_44100 = 44100
sfxr.FREQ_22050 = 22050
sfxr.BITS_FLOAT = 0
sfxr.BITS_16 = 16
sfxr.BITS_8 = 8

-- Utilities

local function trunc(n)
    return math.floor(n - 0.5)
end

local function random(low, high)
    return low + math.random() * (high - low)
end

local function maybe(n)
    return trunc(random(0, n or 1)) == 0
end

local function clamp(n, min, max)
    return math.max(min or -math.huge, math.min(max or math.huge, n))
end

local function cpypol(a, b)
    if b < 0 then
        return -a
    else
        return a
    end
end

local function shallowcopy(t)
    if type(t) == "table" then
        local t2 = {}
        for k,v in pairs(t) do
            t2[k] = v
        end
        return t2
    else
        return t
    end
end

function mergetables(t1, t2)
    for k, v in pairs(t2) do
        if type(v) == "table" then
            if type(t1[k] or false) == "table" then
                mergetables(t1[k] or {}, t2[k] or {})
            else
                t1[k] = v
            end
        else
            t1[k] = v
        end
    end
    return t1
end

local function setseed(seed)
    math.randomseed(seed)
    for i=0, 5 do
        math.random()
    end
end

-- IEEE754 32-bit big-endian floating point numbers
-- source: https://stackoverflow.com/questions/14416734/

local function packIEEE754(number)
	if number == 0 then
		return string.char(0x00, 0x00, 0x00, 0x00)
	elseif number ~= number then
		return string.char(0xFF, 0xFF, 0xFF, 0xFF)
	else
		local sign = 0x00
		if number < 0 then
			sign = 0x80
			number = -number
		end
		local mantissa, exponent = math.frexp(number)
		exponent = exponent + 0x7F
		if exponent <= 0 then
			mantissa = math.ldexp(mantissa, exponent - 1)
			exponent = 0
		elseif exponent > 0 then
			if exponent >= 0xFF then
				return string.char(sign + 0x7F, 0x80, 0x00, 0x00)
			elseif exponent == 1 then
				exponent = 0
			else
				mantissa = mantissa * 2 - 1
				exponent = exponent - 1
			end
		end
		mantissa = math.floor(math.ldexp(mantissa, 23) + 0.5)
		return string.char(
			sign + math.floor(exponent / 2),
			(exponent % 2) * 0x80 + math.floor(mantissa / 0x10000),
			math.floor(mantissa / 0x100) % 0x100,
			mantissa % 0x100)
	end
end

local function unpackIEEE754(packed)
	local b1, b2, b3, b4 = string.byte(packed, 1, 4)
	local exponent = (b1 % 0x80) * 0x02 + math.floor(b2 / 0x80)
	local mantissa = math.ldexp(((b2 % 0x80) * 0x100 + b3) * 0x100 + b4, -23)
	if exponent == 0xFF then
		if mantissa > 0 then
			return 0 / 0
		else
			mantissa = math.huge
			exponent = 0x7F
		end
	elseif exponent > 0 then
		mantissa = mantissa + 1
	else
		exponent = exponent + 1
	end
	if b1 >= 0x80 then
		mantissa = -mantissa
	end
	return math.ldexp(mantissa, exponent - 0x7F)
end

-- Constructor

function sfxr.newSound(...)
    local instance = setmetatable({}, sfxr.Sound)
    instance:__init(...)
    return instance
end

-- The main Sound class

sfxr.Sound = {}
sfxr.Sound.__index = sfxr.Sound

function sfxr.Sound:__init()
    -- Build tables to store the parameters in
    self.volume = {}
    self.envelope = {}
    self.frequency = {}
    self.vibrato = {}
    self.change = {}
    self.duty = {}
    self.phaser = {}
    self.lowpass = {}
    self.highpass = {}

    -- These won't be affected by Sound.resetParameters()
    self.supersamples = 8
    self.volume.master = 0.5
    self.volume.sound = 0.5

    self:resetParameters()
end

function sfxr.Sound:resetParameters()
    -- Set all parameters to the default values
    self.repeatspeed = 0.0
    self.wavetype = sfxr.SQUARE

    self.envelope.attack = 0.0
    self.envelope.sustain = 0.3
    self.envelope.punch = 0.0
    self.envelope.decay = 0.4

    self.frequency.start = 0.3
    self.frequency.min = 0.0
    self.frequency.slide = 0.0
    self.frequency.dslide = 0.0

    self.vibrato.depth = 0.0
    self.vibrato.speed = 0.0
    self.vibrato.delay = 0.0

    self.change.amount = 0.0
    self.change.speed = 0.0
    
    self.duty.ratio = 0.0
    self.duty.sweep = 0.0

    self.phaser.offset = 0.0
    self.phaser.sweep = 0.0

    self.lowpass.cutoff = 1.0
    self.lowpass.sweep = 0.0
    self.lowpass.resonance = 0.0
    self.highpass.cutoff = 0.0
    self.highpass.sweep = 0.0
end

function sfxr.Sound:generate(freq, bits)
    -- Basically the main synthesizing function, yields the sample data

    freq = freq or sfxr.FREQ_44100
    bits = bits or sfxr.BITS_FLOAT
    assert(freq == sfxr.FREQ_44100 or freq == sfxr.FREQ_22050, "Invalid freq argument")
    assert(bits == sfxr.BITS_FLOAT or bits == sfxr.BITS_16 or bits == sfxr.BITS_8, "Invalid bits argument")

    -- Initialize ALL the locals!
    local fperiod, maxperiod
    local slide, dslide
    local square_duty, square_slide
    local chg_mod, chg_time, chg_limit

    local phaserbuffer = {}
    local noisebuffer = {}

    -- Reset the sample buffers
    for i=1, 1025 do
        phaserbuffer[i] = 0
    end

    for i=1, 33 do
        noisebuffer[i] = random(-1, 1)
    end

    local function reset()
        -- subtract 0.017 to match the pitch of the original
        fperiod = 100 / ((self.frequency.start - 0.017)^2 + 0.001)
        maxperiod = 100 / (self.frequency.min^2 + 0.001)
        period = trunc(fperiod)
        
        slide = 1.0 - self.frequency.slide^3 * 0.01
        dslide = -self.frequency.dslide^3 * 0.000001

        square_duty = 0.5 - self.duty.ratio * 0.5
        square_slide = -self.duty.sweep * 0.00005

        if self.change.amount >= 0 then
            chg_mod = 1.0 - self.change.amount^2 * 0.9
        else
            chg_mod = 1.0 - self.change.amount^2 * 10
        end

        chg_time = 0
        chg_limit = 0
        if self.change.speed == 1 then
            chg_limit = 0
        else
            chg_limit = trunc((1 - self.change.speed)^2 * 20000 + 32)
        end
    end
    reset()

    local second_sample = false

    local env_vol = 0
    local env_stage = 1
    local env_time = 0
    local env_length = {self.envelope.attack^2 * 100000,
        self.envelope.sustain^2 * 100000,
        self.envelope.decay^2 * 100000}

    local phase = self.phaser.offset^2 * 1020
    phase = cpypol(phase, self.phaser.offset)
    local dphase = self.phaser.sweep^2
    dphase = cpypol(dphase, self.phaser.sweep)
    local ipp = 0

    local iphase = math.abs(trunc(phase))

    local fltp = 0
    local fltdp = 0
    local fltw = self.lowpass.cutoff^3 * 0.1
    local fltw_d = 1 + self.lowpass.sweep * 0.0001
    local fltdmp = 5 / (1 + self.lowpass.resonance^2 * 20) * (0.01 + fltw)
    fltdmp = clamp(fltdmp, nil, 0.8)
    local fltphp = 0
    local flthp = self.highpass.cutoff^2 * 0.1
    local flthp_d = 1 + self.highpass.sweep * 0.0003

    local vib_phase = 0
    local vib_speed = self.vibrato.speed^2 * 0.01
    local vib_amp = self.vibrato.depth * 0.5

    local rep_time = 0
    local rep_limit = trunc((1 - self.repeatspeed)^2 * 20000 + 32)
    if self.repeatspeed == 0 then
        rep_limit = 0
    end

    -- Yay, the main closure

    local function next()
        -- Repeat maybe
        rep_time = rep_time + 1
        if rep_limit ~= 0 and rep_time >= rep_limit then
            rep_time = 0
            reset()
        end

        -- Update the change time and apply it if needed
        chg_time = chg_time + 1
        if chg_limit ~= 0 and chg_time >= chg_limit then
            chg_limit = 0
            fperiod = fperiod * chg_mod
        end

        -- Apply the frequency slide and stuff
        slide = slide + dslide
        fperiod = fperiod * slide

        if fperiod > maxperiod then
            fperiod = maxperiod
            -- If the frequency is too low, stop generating
            if (self.frequency.min > 0) then
                return nil
            end
        end

        -- Vibrato
        local rfperiod = fperiod
        if vib_amp > 0 then
            vib_phase = vib_phase + vib_speed
            rfperiod = fperiod * (1.0 + math.sin(vib_phase) * vib_amp)
        end

        -- Update the period
        period = trunc(rfperiod)
        if (period < 8) then period = 8 end

        -- Update the square duty
        square_duty = clamp(square_duty + square_slide, 0, 0.5)

        -- Volume envelopes

        env_time = env_time + 1

        if env_time > env_length[env_stage] then
            env_time = 0
            env_stage = env_stage + 1
            -- After the decay stop generating
            if env_stage == 4 then
                return nil
            end
        end

        if env_stage == 1 then
            env_vol = env_time / env_length[1]
        elseif env_stage == 2 then
            env_vol = 1 + (1 - env_time / env_length[2])^1 * 2 * self.envelope.punch
        elseif env_stage == 3 then
            env_vol = 1 - env_time / env_length[3]
        end

        -- Phaser

        phase = phase + dphase
        iphase = clamp(math.abs(trunc(phase)), nil, 1023)

        -- Filter stuff

        if flthp_d ~= 0 then
            flthp = clamp(flthp * flthp_d, 0.00001, 0.1)
        end

        -- And finally the actual tone generation and supersampling

        local ssample = 0
        for si = 0, self.supersamples do
            local sample = 0

            phase = phase + 1

            -- fill the noise buffer every period
            if phase >= period then
                --phase = 0
                phase = phase % period
                if self.wavetype == sfxr.NOISE then
                    for i = 1, 33 do
                        noisebuffer[i] = random(-1, 1)
                    end
                end
            end

            -- Tone oscillators ahead!!!

            -- update the base waveform
            local fp = phase / period

            if self.wavetype == sfxr.SQUARE then
                if fp < square_duty then
                    sample = 0.5
                else
                    sample = -0.5
                end

            elseif self.wavetype == sfxr.SAWTOOTH then
                sample = 1 - fp * 2

            elseif self.wavetype == sfxr.SINE then
                sample = math.sin(fp * 2 * math.pi)

            elseif self.wavetype == sfxr.NOISE then
                sample = noisebuffer[trunc(phase * 32 / period) % 32 + 1]
            end

            -- Apply the lowpass filter to the sample

            local pp = fltp
            fltw = clamp(fltw * fltw_d, 0, 0.1)
            if self.lowpass.cutoff ~= 1 then
                fltdp = fltdp + (sample - fltp) * fltw
                fltdp = fltdp - fltdp * fltdmp
            else
                fltp = sample
                fltdp = 0
            end
            fltp = fltp + fltdp

            -- Apply the highpass filter to the sample

            fltphp = fltphp + (fltp - pp)
            fltphp = fltphp - (fltphp * flthp)
            sample = fltphp

            -- Apply the phaser to the sample

            phaserbuffer[bit.band(ipp, 1023) + 1] = sample
            sample = sample + phaserbuffer[bit.band(ipp - iphase + 1024, 1023) + 1]
            ipp = bit.band(ipp + 1, 1023)

            -- Accumulation and envelope application
            ssample = ssample + sample * env_vol
        end

        -- Apply the volumes
        ssample = (ssample / self.supersamples) * self.volume.master
        ssample = ssample * (2 * self.volume.sound)

        -- Hard limit
        ssample = clamp(ssample, -1, 1)

        -- Frequency conversion
        second_sample = not second_sample
        if freq == sfxr.FREQ_22050 and second_sample then
            -- hah!
            local nsample = next()
            if nsample then
                return (ssample + nsample) / 2
            else
                return nil
            end
        end

        -- bit conversions
        if bits == sfxr.BITS_FLOAT then
            return ssample
        elseif bits == sfxr.BITS_16 then
            return trunc(ssample * 32000)
        else
            return trunc(ssample * 127 + 128)
        end
    end

    return next
end

function sfxr.Sound:getEnvelopeLimit(freq)
    local env_length = {self.envelope.attack^2 * 100000,
        self.envelope.sustain^2 * 100000,
        self.envelope.decay^2 * 100000}
    local limit = trunc(env_length[1] + env_length[2] + env_length[3] + 2)
    
    if freq == nil or freq == sfxr.FREQ_44100 then
        return limit
    elseif freq == sfxr.FREQ_22050 then
        return math.ceil(limit / 2)
    else
        error("Invalid freq argument")
    end
end

function sfxr.Sound:generateTable(freq, bits)
    local t = {}
    local i = 1
    for v in self:generate(freq, bits) do
        t[i] = v
        i = i + 1
    end
    return t
end

function sfxr.Sound:generateString(freq, bits, endianness)
    assert(bits == sfxr.BITS_16 or bits == sfxr.BITS_8, "Invalid bits argument")
    assert(endianness == "big" or endianness == "little", "Invalid endianness")
    local s = ""

    local buf = {}
    buf[100] = 0
    local i = 1

    for v in self:generate(freq, bits) do
        if bits == sfxr.BITS_8 then
            buf[i] = v
            i = i + 1
        else
            if endianness == "big" then
                buf[i] = bit.rshift(v, 8)
                buf[i + 1] = bit.band(v, 0xFF)
                i = i + 2
            else
                buf[i] = bit.band(v, 0xFF)
                buf[i + 1] = bit.rshift(v, 8)
                i = i + 2
            end
        end

        if i >= 100 then
            s = s .. string.char(unpack(buf))
            i = 0
        end
    end

    s = s .. string.char(unpack(buf, i, 100))
    return s
end

function sfxr.Sound:generateSoundData(freq, bits)
    freq = freq or sfxr.FREQ_44100
    local tab = self:generateTable(freq, sfxr.BITS_FLOAT)

    if #tab == 0 then
        return nil
    end

    local data = love.sound.newSoundData(#tab, freq, bits, 1)

    for i = 0, #tab - 1 do
        data:setSample(i, tab[i + 1])
    end

    return data
end

function sfxr.Sound:play(freq, bits)
    local data = self:generateSoundData(freq, bits)

    if data then
        local source = love.audio.newSource(data)
        source:play()
        return source
    end
end

function sfxr.Sound:randomize(seed)
    if seed then setseed(seed) end

    local wavetype = self.wavetype
    self:resetParameters()
    self.wavetype = wavetype

    if maybe() then
        self.repeatspeed = random(0, 1)
    end

    if maybe() then
        self.frequency.start = random(-1, 1)^3 + 0.5
    else
        self.frequency.start = random(-1, 1)^2
    end
    self.frequency.limit = 0
    self.frequency.slide = random(-1, 1)^5
    if self.frequency.start > 0.7 and self.frequency.slide > 0.2 then
        self.frequency.slide = -self.frequency.slide
    elseif self.frequency.start < 0.2 and self.frequency.slide <-0.05 then
        self.frequency.slide = -self.frequency.slide
    end
    self.frequency.dslide = random(-1, 1)^3

    self.duty.ratio = random(-1, 1)
    self.duty.sweep = random(-1, 1)^3

    self.vibrato.depth = random(-1, 1)^3
    self.vibrato.speed = random(-1, 1)
    self.vibrato.delay = random(-1, 1)

    self.envelope.attack = random(-1, 1)^3
    self.envelope.sustain = random(-1, 1)^2
    self.envelope.punch = random(-1, 1)^2
    self.envelope.decay = random(-1, 1)
    
    if self.envelope.attack + self.envelope.sustain + self.envelope.decay < 0.2 then
        self.envelope.sustain = self.envelope.sustain + 0.2 + random(0, 0.3)
        self.envelope.decay = self.envelope.decay + 0.2 + random(0, 0.3)
    end

    self.lowpass.resonance = random(-1, 1)
    self.lowpass.cutoff = 1 - random(0, 1)^3
    self.lowpass.sweep = random(-1, 1)^3
    if self.lowpass.cutoff < 0.1 and self.lowpass.sweep < -0.05 then
        self.lowpass.sweep = -self.lowpass.sweep
    end
    self.highpass.cutoff = random(0, 1)^3
    self.highpass.sweep = random(-1, 1)^5

    self.phaser.offset = random(-1, 1)^3
    self.phaser.sweep = random(-1, 1)^3

    self.change.speed = random(-1, 1)
    self.change.amount = random(-1, 1)
end

function sfxr.Sound:mutate(amount, seed, changeFreq)
    if seed then setseed(seed) end
    local amount = (amount or 1)
    local a = amount / 20
    local b = (1 - a) * 10
    local changeFreq = changeFreq or true

    if changeFreq == true then
        if maybe(b) then self.frequency.start = self.frequency.start + random(-a, a) end
        if maybe(b) then self.frequency.slide = self.frequency.slide + random(-a, a) end
        if maybe(b) then self.frequency.dslide = self.frequency.dslide + random(-a, a) end
    end

    if maybe(b) then self.duty.ratio = self.duty.ratio + random(-a, a) end
    if maybe(b) then self.duty.sweep = self.duty.sweep + random(-a, a) end

    if maybe(b) then self.vibrato.depth = self.vibrato.depth + random(-a, a) end
    if maybe(b) then self.vibrato.speed = self.vibrato.speed + random(-a, a) end
    if maybe(b) then self.vibrato.delay = self.vibrato.delay + random(-a, a) end

    if maybe(b) then self.envelope.attack = self.envelope.attack + random(-a, a) end
    if maybe(b) then self.envelope.sustain = self.envelope.sustain + random(-a, a) end
    if maybe(b) then self.envelope.punch = self.envelope.punch + random(-a, a) end
    if maybe(b) then self.envelope.decay = self.envelope.decay + random(-a, a) end

    if maybe(b) then self.lowpass.resonance = self.lowpass.resonance + random(-a, a) end
    if maybe(b) then self.lowpass.cutoff = self.lowpass.cutoff + random(-a, a) end
    if maybe(b) then self.lowpass.sweep = self.lowpass.sweep + random(-a, a) end
    if maybe(b) then self.highpass.cutoff = self.highpass.cutoff + random(-a, a) end
    if maybe(b) then self.highpass.sweep = self.highpass.sweep + random(-a, a) end

    if maybe(b) then self.phaser.offset = self.phaser.offset + random(-a, a) end
    if maybe(b) then self.phaser.sweep = self.phaser.sweep + random(-a, a) end

    if maybe(b) then self.change.speed = self.change.speed + random(-a, a) end
    if maybe(b) then self.change.amount = self.change.amount + random(-a, a) end

    if maybe(b) then self.repeatspeed = self.repeatspeed + random(-a, a) end
end

function sfxr.Sound:randomPickup(seed)
    if seed then setseed(seed) end
    self:resetParameters()
    self.frequency.start = random(0.4, 0.5)
    self.envelope.attack = 0
    self.envelope.sustain = random(0, 0.1)
    self.envelope.punch = random(0.3, 0.6)
    self.envelope.decay = random(0.1, 0.5)
    
    if maybe() then
        self.change.speed = random(0.5, 0.7)
        self.change.amount = random(0.4, 0.6)
    end
end

function sfxr.Sound:randomLaser(seed)
    if seed then setseed(seed) end
    self:resetParameters()
    self.wavetype = trunc(random(0, 2)) + 1
    if self.wavetype == sfxr.SINE and maybe() then
        self.wavetype = trunc(random(0, 1)) + 1
    end

    if maybe(2) then
        self.frequency.start = random(0.3, 0.9)
        self.frequency.min = random(0, 0.1)
        self.frequency.slide = -0.35 - random(0, 0.3)
    else
        self.frequency.start = random(0.5, 1)
        self.frequency.min = clamp(self.frequency.start - 0.5 - random(0, 0.6), 0.2)
        self.frequency.slide = -0.15 - random(0, 0.2)
    end

    if maybe() then
        self.duty.ratio = random(0, 0.5)
        self.duty.sweep = random(0, 0.2)
    else
        self.duty.ratio = random(0.4, 0.9)
        self.duty.sweep = -random(0, 0.7)
    end

    self.envelope.attack = 0
    self.envelope.sustain = random(0.1, 0.3)
    self.envelope.decay = random(0, 0.4)

    if maybe() then
        self.envelope.punch = random(0, 0.3)
    end

    if maybe(2) then
        self.phaser.offset = random(0, 0.2)
        self.phaser.sweep = -random(0, 0.2)
    end

    if maybe() then
        self.highpass.cutoff = random(0, 0.3)
    end
end

function sfxr.Sound:randomExplosion(seed)
    if seed then setseed(seed) end
    self:resetParameters()
    self.wavetype = sfxr.NOISE
    
    if maybe() then
        self.frequency.start = random(0.1, 0.5)
        self.frequency.slide = random(-0.1, 0.3)
    else
        self.frequency.start = random(0.2, 0.9)
        self.frequency.slide = -0.2 - random(0, 0.2)
    end
    self.frequency.start = self.frequency.start^2

    if maybe(4) then
        self.frequency.slide = 0
    end
    if maybe(2) then
        self.repeatspeed = random(0.3, 0.8)
    end

    self.envelope.attack = 0
    self.envelope.sustain = random(0.1, 0.4)
    self.envelope.punch = random(0.2, 0.8)
    self.envelope.decay = random(0, 0.5)

    if maybe() then
        self.phaser.offset = random(-0.3, 0.6)
        self.phaser.sweep = -random(0, 0.3)
    end
    if maybe(2) then
        self.change.speed = random(0.6, 0.8)
        self.change.amount = random(0.8, 2.4)
    elseif maybe() then
        self.change.amount = random(0, 0.7)
        self.change.speed = random(0, 0.6)
    end
end

function sfxr.Sound:randomPowerup(seed)
    if seed then setseed(seed) end
    self:resetParameters()
    if maybe() then
        self.wavetype = sfxr.SAWTOOTH
    else
        self.duty.ratio = random(0, 0.6)
    end

    if maybe() then
        self.frequency.start = random(0.2, 0.5)
        self.frequency.slide = random(0.1, 0.5)
        self.repeatspeed = random(0.4, 0.8)
    else
        self.frequency.start = random(0.2, 0.5)
        self.frequency.slide = random(0.1, 0.5)
        if maybe() then
            self.change.amount = random(0, 0.7)
            self.change.speed = random(0, 0.6)
        end
    end
    self.envelope.attack = 0
    self.envelope.sustain = random(0, 0.4)
    self.envelope.decay = random(0.1, 0.5)
end

function sfxr.Sound:randomHit(seed)
    if seed then setseed(seed) end
    self:resetParameters()
    self.wavetype = trunc(random(0, 2)) + 1

    if self.wavetype == sfxr.SINE then
        self.wavetype = 3
    elseif self.wavetype == sfxr.SQUARE then
        self.duty.ratio = random(0, 0.6)
    end

    self.frequency.start = random(0.2, 0.8)
    self.frequency.slide = -0.3 - random(0, 0.4)
    self.envelope.attack = 0
    self.envelope.sustain = random(0, 0.1)
    self.envelope.decay = random(0.1, 0.3)

    if maybe() then
        self.highpass.cutoff = random(0, 0.3)
    end
end

function sfxr.Sound:randomJump(seed)
    if seed then setseed(seed) end
    self:resetParameters()
    self.wavetype = sfxr.SQUARE

    self.duty.value = random(0, 0.6)
    self.frequency.cutoff = random(0.3, 0.6)
    self.frequency.slide = random(0.1, 0.3)

    self.envelope.attack = 0
    self.envelope.sustain = random(0.1, 0.4)
    self.envelope.decay = random(0.1, 0.3)

    if maybe() then
        self.highpass.cutoff = random(0, 0.3)
    end
    if maybe() then
        self.lowpass.cutoff = 1 - random(0, 0.6)
    end
end

function sfxr.Sound:randomBlip(seed)
    if seed then setseed(seed) end
    self:resetParameters()
    self.wavetype = trunc(random(0, 1)) + 1

    if self.wavetype == 0 then
        self.duty.ratio = random(0, 0.6)
    end

    self.frequency.start = random(0.2, 0.6)
    self.envelope.attack = 0
    self.envelope.sustain = random(0.1, 0.2)
    self.envelope.decay = random(0, 0.2)
    self.highpass.cutoff = 0.1
end

function sfxr.Sound:exportWAV(f, freq, bits)
    freq = freq or sfxr.FREQ_44100
    bits = bits or sfxr.BITS_16
    assert(freq == sfxr.FREQ_44100 or freq == sfxr.FREQ_22050, "Invalid freq argument")
    assert(bits == sfxr.BITS_16 or bits == sfxr.BITS_8, "Invalid bits argument")

    local close = false
    if type(f) == "string" then
        f = io.open(f, "wb")
        close = true
    end

    -- Some utility functions
    function seek(pos)
        if io.type(f) == "file" then
            f:seek("set", pos)
        else
            f:seek(pos)
        end
    end

    function tell()
        if io.type(f) == "file" then
            return f:seek()
        else
            return f:tell()
        end
    end

    function bytes(num, len)
        local str = ""
        for i = 1, len do
            str = str .. string.char(num % 256)
            num = math.floor(num / 256)
        end
        return str
    end

    function w16(num)
        f:write(bytes(num, 2))
    end

    function w32(num)
        f:write(bytes(num, 4))
    end

    function ws(str)
        f:write(str)
    end

    -- These will hold important file positions
    local pos_fsize
    local pos_csize

    -- Start the file by writing the RIFF header
    ws("RIFF")
    pos_fsize = tell()
    w32(0) -- remaining file size, will be replaced later
    ws("WAVE") -- type

    -- Write the format chunk
    ws("fmt ")
    w32(16) -- chunk size
    w16(1) -- compression code (1 = PCM)
    w16(1) -- channel number
    w32(freq) -- sample rate
    w32(freq * bits / 8) -- bytes per second
    w16(bits / 8) -- block alignment
    w16(bits) -- bits per sample

    -- Write the header of the data chunk
    ws("data")
    pos_csize = tell()
    w32(0) -- chunk size, will be replaced later

    -- Aand write the actual sample data
    local samples = 0

    for v in self:generate(freq, bits) do
        samples = samples + 1

        if bits == sfxr.BITS_16 then
            -- wrap around a bit
            if v >= 256^2 then v = 0 end
            if v < 0 then v = 256^2 - 1 end
            w16(v)
        else
            f:write(string.char(v))
        end
    end

    -- Seek back to the stored positions
    seek(pos_fsize)
    w32(pos_csize - 4 + samples * bits / 8) -- remaining file size
    seek(pos_csize)
    w32(samples * bits / 8) -- chunk size

    if close then
        f:close()
    end
end

function sfxr.Sound:save(f, compressed)
    local close = false
    if type(f) == "string" then
        f = io.open(f, "w")
        close = true
    end

    local code = "local "

    -- we'll compare the current parameters with the defaults
    local defaults = sfxr.newSound()

    -- this part is pretty awful but it works for now
    function store(keys, obj)
        local name = keys[#keys]

        if type(obj) == "number" then
            -- fetch the default value
            local def = defaults
            for i=2, #keys do
                def = def[keys[i]]
            end

            if obj ~= def then
                local k = table.concat(keys, ".")
                if not compressed then
                    code = code .. "\n" .. string.rep(" ", #keys - 1)
                end
                code = code .. string.format("%s=%s;", name, obj)
            end

        elseif type(obj) == "table" then
            local spacing = compressed and "" or "\n" .. string.rep(" ", #keys - 1)
            code = code .. spacing .. string.format("%s={", name)

            for k, v in pairs(obj) do
                local newkeys = shallowcopy(keys)
                newkeys[#newkeys + 1] = k
                store(newkeys, v)
            end

            code = code .. spacing .. "};"
        end
    end

    store({"s"}, self)
    code = code .. "\nreturn s, \"" .. sfxr.VERSION .. "\"" 
    f:write(code)

    if close then
        f:close()
    end
end

function sfxr.Sound:load(f)
    local close = false
    if type(f) == "string" then
        f = io.open(f, "r")
        close = true
    end

    local code
    if io.type(f) == "file" then
        code = f:read("*a")
    else
        code = f:read()
    end

    local params, version = assert(loadstring(code))()
    -- check version compatibility
    if version > sfxr.VERSION then
        return version
    end

    -- merge the loaded table into the own
    mergetables(self, params)

    if close then
        f:close()
    end
end

function sfxr.Sound:saveBinary(f)
    local close = false
    if type(f) == "string" then
        f = io.open(f, "w")
        close = true
    end

    function writeFloat(x)
        local packed = packIEEE754(x):reverse()
        assert(packed:len() == 4)
        f:write(packed)
    end

    f:write('\x66\x00\x00\x00') -- version 102
    assert(self.wavetype < 256)
    f:write(string.char(self.wavetype) .. '\x00\x00\x00')
    writeFloat(self.volume.sound)

    writeFloat(self.frequency.start)
    writeFloat(self.frequency.min)
    writeFloat(self.frequency.slide)
    writeFloat(self.frequency.dslide)
    writeFloat(self.duty.ratio)
    writeFloat(self.duty.sweep)

    writeFloat(self.vibrato.depth)
    writeFloat(self.vibrato.speed)
    writeFloat(self.vibrato.delay)

    writeFloat(self.envelope.attack)
    writeFloat(self.envelope.sustain)
    writeFloat(self.envelope.decay)
    writeFloat(self.envelope.punch)

    f:write('\x00') -- unused filter_on boolean
    writeFloat(self.lowpass.resonance)
    writeFloat(self.lowpass.cutoff)
    writeFloat(self.lowpass.sweep)
    writeFloat(self.highpass.cutoff)
    writeFloat(self.highpass.sweep)

    writeFloat(self.phaser.offset)
    writeFloat(self.phaser.sweep)

    writeFloat(self.repeatspeed)

    writeFloat(self.change.speed)
    writeFloat(self.change.amount)

    if close then
        f:close()
    end
end

function sfxr.Sound:loadBinary(f)
    local close = false
    if type(f) == "string" then
        f = io.open(f, "r")
        close = true
    end

    local s
    if io.type(f) == "file" then
        s = f:read("*a")
    else
        s = f:read()
    end

    if close then
        f:close()
    end

    local off = 1

    local function readFloat()
        local f = unpackIEEE754(s:sub(off, off+3):reverse())
        off = off + 4
        return f
    end

    -- Start reading the string

    local version = s:byte(off)
    off = off + 4
    if version < 100 or version > 102 then
        return nil, "unknown version number "..version
    end

    self.wavetype = s:byte(off)
    off = off + 4
    self.volume.sound = version==102 and readFloat() or 0.5

    self.frequency.start = readFloat()
    self.frequency.min = readFloat()
    self.frequency.slide = readFloat()
    self.frequency.dslide = version>=101 and readFloat() or 0

    self.duty.ratio = readFloat()
    self.duty.sweep = readFloat()

    self.vibrato.depth = readFloat()
    self.vibrato.speed = readFloat()
    self.vibrato.delay = readFloat()

    self.envelope.attack = readFloat()
    self.envelope.sustain = readFloat()
    self.envelope.decay = readFloat()
    self.envelope.punch = readFloat()

    off = off + 1 -- filter_on - seems to be ignored in the C++ version
    self.lowpass.resonance = readFloat()
    self.lowpass.cutoff = readFloat()
    self.lowpass.sweep = readFloat()
    self.highpass.cutoff = readFloat()
    self.highpass.sweep = readFloat()

    self.phaser.offset = readFloat()
    self.phaser.sweep = readFloat()

    self.repeatspeed = readFloat()

    if version >= 101 then
        self.change.speed = readFloat()
        self.change.amount = readFloat()
    end

    assert(off-1 == s:len())
end

return sfxr