5.4.1 Audio Files

Sound data is represented by a special <audio> data type that stores not only the audio samples themselves, but metadata such as sample rate, number of channels, and how many bits are used for each sample.

Procedure: load-audio file-name [#:mode static]

Load audio within file-name. The following file formats are currently supported:

• WAV
• MP3
• Ogg Vorbis

Audio files can be loaded in two different ways, as indicated by mode:

• static: Load the entire audio file into memory.
• stream: Load chunks of the audio file as needed.

Generally speaking, sound effects don’t take up much space and should be loaded statically, but music files are much larger and should use streaming. Static loading is the default.

Procedure: audio? obj

Return #t if obj is an audio object.

Procedure: streaming-audio? audio

Return #t if audio uses stream loading.

Procedure: static-audio?

Return #t if audio uses static loading.

Procedure: audio-mode audio

Return the loading mode for audio, either static or stream.

Procedure: audio-duration audio

Return the duration of audio in seconds.

Procedure: audio-bits-per-sample audio

Return the number of bits per sample in audio.

Procedure: audio-channels audio

Return the number of channels in audio.

Procedure: audio-sample-rate audio

Return the sample rate of audio.

Procedure: audio-play audio [#:pitch 1.0] [#:volume 1.0] [#:min-volume 0.0] [#:max-volume 1.0] [#:max-distance] [#:reference-distance 0.0] [#:rolloff-factor 1.0] [#:cone-outer-volume 0.0] [#:cone-inner-angle 0.0] [#:cone-outer-angle] [#:position (vec3 0.0 0.0 0.0)] [#:velocity (vec3 0.0 0.0 0.0)] [#:direction (vec3 0.0 0.0 0.0)] [#:relative? #f]

Play audio. There are many, many knobs to tweak that will affect the sound that comes out of the player’s speakers.:

• pitch: Pitch multiplier. The default value of 1.0 means no change in pitch.
• volume: Volume multiplier. The default value of 1.0 means no change in volume.
• min-volume: Minimum volume.
• max-volume: Maximum volume.
• max-distance: Used with the inverse clamped distance model (the default model) to set the distance where there will no longer be any attenuation of the source.
• reference-distance: The distance where the volume for the audio would drop by half (before being influenced by the rolloff factor or maximum distance.)
• rolloff-factor: For slowing down or speeding up the rate of attenuation. The default of 1.0 means no attenuation adjustment is made.
• cone-outer-volume: The volume when outside the oriented cone.
• cone-inner-angle: Inner angle of the sound cone, in radians. The default value is 0.
• cone-outer-angle: Outer angle of the sound cone, in radians. The default value is 2pi radians, or 360 degrees.
• position: The source of the sound emitter in 3D space.
• velocity: The velocity of the sound emitter in 3D space.
• direction: The direction of the sound emitter in 3D space.
• relative?: A flag that determines whether the position is in absolute coordinates or relative to the listener’s location. Absolute coordinates are used by default.

For games with basic sound needs (that is to say they don’t need 3D sound modeling), the only things that really matter are volume and pitch.