Sound API documentation

Version: stable

FUNCTION
sound.is_music_playing() check if background music is playing
sound.get_rms() get RMS value from mixer group
sound.get_peak() get peak gain value from mixer group
sound.set_group_gain() set mixer group gain
sound.get_group_gain() get mixer group gain
sound.get_groups() get all mixer group names
sound.get_group_name() get mixer group name string
sound.is_phone_call_active() check if a phone call is active
sound.play() plays a sound
sound.stop() stop a playing a sound(s)
sound.pause() pause a playing a sound(s)
sound.set_gain() set sound gain
sound.set_pan() set sound pan
MESSAGE
play_sound plays a sound
stop_sound stop a playing a sound(s)
set_gain set sound gain
sound_done reports when a sound has finished playing
PROPERTIES
gain number sound gain
pan number sound pan
speed number sound speed
sound hash sound data

Functions

sound.is_music_playing()

sound.is_music_playing()

Checks if background music is playing, e.g. from iTunes. On non mobile platforms, this function always return false. On Android you can only get a correct reading of this state if your game is not playing any sounds itself. This is a limitation in the Android SDK. If your game is playing any sounds, even with a gain of zero, this function will return false. The best time to call this function is:

  • In the init function of your main collection script before any sounds are triggered
  • In a window listener callback when the window.WINDOW_EVENT_FOCUS_GAINED event is received
Both those times will give you a correct reading of the state even when your application is swapped out and in while playing sounds and it works equally well on Android and iOS.

PARAMETERS

RETURNS

playing boolean true if music is playing, otherwise false.

EXAMPLES

If music is playing, mute "master": 
if sound.is_music_playing() then
    -- mute "master"
    sound.set_group_gain("master", 0)
end

sound.get_rms()

sound.get_rms(group,window)

Get RMS (Root Mean Square) value from mixer group. This value is the square root of the mean (average) value of the squared function of the instantaneous values. For instance: for a sinewave signal with a peak gain of -1.94 dB (0.8 linear), the RMS is 0.8 × 1/sqrt(2) which is about 0.566. Note the returned value might be an approximation and in particular the effective window might be larger than specified.

PARAMETERS

group string, hash group name
window number window length in seconds

RETURNS

rms_l number RMS value for left channel
rms_r number RMS value for right channel

EXAMPLES

Get the RMS from the "master" group where a mono -1.94 dB sinewave is playing: 
local rms = sound.get_rms("master", 0.1) -- throw away right channel.
print(rms) --> 0.56555819511414

sound.get_peak()

sound.get_peak(group,window)

Get peak value from mixer group. Note that gain is in linear scale, between 0 and 1. To get the dB value from the gain, use the formula 20 * log(gain). Inversely, to find the linear value from a dB value, use the formula 10db/20. Also note that the returned value might be an approximation and in particular the effective window might be larger than specified.

PARAMETERS

group string, hash group name
window number window length in seconds

RETURNS

peak_l number peak value for left channel
peak_r number peak value for right channel

EXAMPLES

Get the peak gain from the "master" group and convert to dB for displaying: 
local left_p, right_p = sound.get_peak("master", 0.1)
left_p_db = 20 * log(left_p)
right_p_db = 20 * log(right_p)

sound.set_group_gain()

sound.set_group_gain(group,gain)

Set mixer group gain Note that gain is in linear scale, between 0 and 1. To get the dB value from the gain, use the formula 20 * log(gain). Inversely, to find the linear value from a dB value, use the formula 10db/20.

PARAMETERS

group string, hash group name
gain number gain in linear scale

EXAMPLES

Set mixer group gain on the "soundfx" group to -4 dB: 
local gain_db = -4
local gain = 10^gain_db/20 -- 0.63095734448019
sound.set_group_gain("soundfx", gain)

sound.get_group_gain()

sound.get_group_gain(group)

Get mixer group gain Note that gain is in linear scale, between 0 and 1. To get the dB value from the gain, use the formula 20 * log(gain). Inversely, to find the linear value from a dB value, use the formula 10db/20.

PARAMETERS

group string, hash group name

RETURNS

gain number gain in linear scale

EXAMPLES

Get the mixer group gain for the "soundfx" and convert to dB: 
local gain = sound.get_group_gain("soundfx")
local gain_db = 20 * log(gain)

sound.get_groups()

sound.get_groups()

Get a table of all mixer group names (hashes).

PARAMETERS

RETURNS

groups table table of mixer group names

EXAMPLES

Get the mixer groups, set all gains to 0 except for "master" and "soundfx" where gain is set to 1: 
local groups = sound.get_groups()
for _,group in ipairs(groups) do
    if group == hash("master") or group == hash("soundfx") then
        sound.set_group_gain(group, 1)
    else
        sound.set_group_gain(group, 0)
    end
end

sound.get_group_name()

sound.get_group_name(group)

Get a mixer group name as a string. This function is to be used for debugging and development tooling only. The function does a reverse hash lookup, which does not return a proper string value when the game is built in release mode.

PARAMETERS

group string, hash group name

RETURNS

name string group name

EXAMPLES

Get the mixer group string names so we can show them as labels on a dev mixer overlay: 
local groups = sound.get_groups()
for _,group in ipairs(groups) do
    local name = sound.get_group_name(group)
    msg.post("/mixer_overlay#gui", "set_mixer_label", { group = group, label = name})
end

sound.is_phone_call_active()

sound.is_phone_call_active()

Checks if a phone call is active. If there is an active phone call all other sounds will be muted until the phone call is finished. On non mobile platforms, this function always return false.

PARAMETERS

RETURNS

call_active boolean true if there is an active phone call, false otherwise.

EXAMPLES

Test if a phone call is on-going: 
if sound.is_phone_call_active() then
    -- do something sensible.
end

sound.play()

sound.play(url,[play_properties],[complete_function])

Make the sound component play its sound. Multiple voices are supported. The limit is set to 32 voices per sound component. Note that gain is in linear scale, between 0 and 1. To get the dB value from the gain, use the formula 20 * log(gain). Inversely, to find the linear value from a dB value, use the formula 10db/20. A sound will continue to play even if the game object the sound component belonged to is deleted. You can call sound.stop() to stop the sound.

PARAMETERS

url string, hash, url the sound that should play
[play_properties] table
optional table with properties:
delay
number delay in seconds before the sound starts playing, default is 0.
gain
number sound gain between 0 and 1, default is 1. The final gain of the sound will be a combination of this gain, the group gain and the master gain.
pan
number sound pan between -1 and 1, default is 0. The final pan of the sound will be an addition of this pan and the sound pan.
speed
number sound speed where 1.0 is normal speed, 0.5 is half speed and 2.0 is double speed. The final speed of the sound will be a multiplication of this speed and the sound speed.
[complete_function] function(self, message_id, message, sender)) function to call when the sound has finished playing.
self
object The current object.
message_id
hash The name of the completion message, "sound_done".
message
table Information about the completion:
  • number play_id - the sequential play identifier that was given by the sound.play function.
sender
url The invoker of the callback: the sound component.

RETURNS

id number The identifier for the sound voice

EXAMPLES

Assuming the script belongs to an instance with a sound-component with id "sound", this will make the component play its sound after 1 second: 
sound.play("#sound", { delay = 1, gain = 0.5, pan = -1.0 } )
Using the callback argument, you can chain several sounds together: 
local function sound_done(self, message_id, message, sender)
  -- play 'boom' sound fx when the countdown has completed
  if message_id == hash("sound_done") and message.play_id == self.countdown_id then
    sound.play("#boom", nil, sound_done)
  end
end

function init(self)
  self.countdown_id = sound.play("#countdown", nil, sound_done)
end

sound.stop()

sound.stop(url)

Stop playing all active voices

PARAMETERS

url string, hash, url the sound that should stop

EXAMPLES

Assuming the script belongs to an instance with a sound-component with id "sound", this will make the component stop all playing voices: 
sound.stop("#sound")

sound.pause()

sound.pause(url,pause)

Pause all active voices

PARAMETERS

url string, hash, url the sound that should pause
pause bool true if the sound should pause

EXAMPLES

Assuming the script belongs to an instance with a sound-component with id "sound", this will make the component pause all playing voices: 
sound.pause("#sound", true)

sound.set_gain()

sound.set_gain(url,[gain])

Set gain on all active playing voices of a sound. Note that gain is in linear scale, between 0 and 1. To get the dB value from the gain, use the formula 20 * log(gain). Inversely, to find the linear value from a dB value, use the formula 10db/20.

PARAMETERS

url string, hash, url the sound to set the gain of
[gain] number sound gain between 0 and 1. The final gain of the sound will be a combination of this gain, the group gain and the master gain.

EXAMPLES

Assuming the script belongs to an instance with a sound-component with id "sound", this will set the gain to 0.5 
sound.set_gain("#sound", 0.5)

sound.set_pan()

sound.set_pan(url,[pan])

Set panning on all active playing voices of a sound. The valid range is from -1.0 to 1.0, representing -45 degrees left, to +45 degrees right.

PARAMETERS

url string, hash, url the sound to set the panning value to
[pan] number sound panning between -1.0 and 1.0

EXAMPLES

Assuming the script belongs to an instance with a sound-component with id "sound", this will set the gain to 0.5 
sound.set_pan("#sound", 0.5) -- pan to the right

Messages

play_sound

Post this message to a sound-component to make it play its sound. Multiple voices is supported. The limit is set to 32 voices per sound component. Note that gain is in linear scale, between 0 and 1. To get the dB value from the gain, use the formula 20 * log(gain). Inversely, to find the linear value from a dB value, use the formula 10db/20. A sound will continue to play even if the game object the sound component belonged to is deleted. You can send a stop_sound to stop the sound.

[delay] number delay in seconds before the sound starts playing, default is 0.
[gain] number sound gain between 0 and 1, default is 1.
[play_id] number the identifier of the sound, can be used to distinguish between consecutive plays from the same component.

EXAMPLES

Assuming the script belongs to an instance with a sound-component with id "sound", this will make the component play its sound after 1 second: 
msg.post("#sound", "play_sound", {delay = 1, gain = 0.5})

stop_sound

Post this message to a sound-component to make it stop playing all active voices

EXAMPLES

Assuming the script belongs to an instance with a sound-component with id "sound", this will make the component stop all playing voices: 
msg.post("#sound", "stop_sound")

set_gain

Post this message to a sound-component to set gain on all active playing voices. Note that gain is in linear scale, between 0 and 1. To get the dB value from the gain, use the formula 20 * log(gain). Inversely, to find the linear value from a dB value, use the formula 10db/20.

[gain] number sound gain between 0 and 1, default is 1.

EXAMPLES

Assuming the script belongs to an instance with a sound-component with id "sound", this will set the gain to 0.5 
msg.post("#sound", "set_gain", {gain = 0.5})

sound_done

This message is sent back to the sender of a play_sound message, if the sound could be played to completion.

[play_id] number id number supplied when the message was posted.

Properties

gain

The gain on the sound-component. Note that gain is in linear scale, between 0 and 1.

EXAMPLES

function init(self)
  local gain = go.get("#sound", "gain")
  go.set("#sound", "gain", gain * 1.5)
end

pan

The pan on the sound-component. The valid range is from -1.0 to 1.0, representing -45 degrees left, to +45 degrees right.

EXAMPLES

function init(self)
  local pan = go.get("#sound", "pan")
  go.set("#sound", "pan", pan * -1)
end

speed

The speed on the sound-component where 1.0 is normal speed, 0.5 is half speed and 2.0 is double speed.

EXAMPLES

function init(self)
  local speed = go.get("#sound", "speed")
  go.set("#sound", "speed", speed * 0.5)
end

sound

The sound data used when playing the sound. The type of the property is hash.

EXAMPLES

How to change the sound: 
function init(self)
  -- load a wav file bundled as a custom resource
  local wav = sys.load_resource("foo.wav")
  -- get resource path to the sound component
  local resource_path = go.get("#sound", "sound")
  -- update the resource with the loaded wav file
  resource.set_sound(resource_path, wav)
  -- play the updated sound
  sound.play("#sound")
end