5. Scheduling of events

Scheduling Web Audio with precision

• A Tale of Two Clocks

• the two clocks: Web Audio Clock & JavaScript Clock

Web Audio Clock

• access to audio subsystem’s hardware clock
• currentTime property for audio clock, floating-point number of seconds
• starting and stopping sounds, schedules changes to the sound (changing frequency or volume)
• schedules paramenters and audio events
• high-precision
• returns value in sound sample level (15 decimal digits of precision)

JavaScript Clock

• Date.now() and setTimeout()
• useful callback window.setTimeout() and window.setInterval() to call code back
• not very precise
• Date.now() returns value in milliseconds
• sensitive to other things happening on main JavaScript thread, may cause in too-immediate or delayed playback of audio files

Scheduling methods and parameters

• start() and stop() (previously known as noteOn and noteOff)
• Web Audio Clock: set*ValueAtTime() methods: linearRampToValueAtTime(), exponentialRampToValueAtTime(), setTargetAtTime(), setValueCurveAtTime(), cancelScheduledValues
• JavaScript Clock: setTimeout(), scheduleNote(), nextNote()

Synchronous vs Asynchronous

• Synchronous: happening at the same time (real-time)
• might have conflict in timing
• waits for one task to finsh before moving on to another task
• happens in a single series
• Asynchronous: not blocking the main JavaScript execution thread
• Happening at different times, fast-paced
• able to move on to another task before the previous one finishes
• different routines able to run in background

LINKS:

• ArrayBuffer
• Load and decode sound files
• Audio formats codec
• Media (video & audio) formats codec
• Audio format tests
• A Tale of Two clocks
• Synchronous vs Asynchronous