I’ve shown you how to create two rhythms by triggering three buffered audio files at specific time intervals. Var source = context.createBufferSource() įunction startPlayingRhythm1(bufferList) Timed Rhythms with Web Audio API and JavaScript Change the path and filename of the audio files to match yours and you’ve got it! window.onload = init Īlert("Web Audio API is not supported in this browser") Here’s the full code to create two different rhythms in JavaScript with the Web Audio API. The function for the second rhythm is similar to the first, but has a different tempo and of course different time specifications for the individual sounds. We could also achieve the same result with the following code. PlaySound(kick, startTime + 3*quarterNoteTime) PlaySound(kick, startTime + 2*quarterNoteTime) PlaySound(kick, startTime + quarterNoteTime) For example, to play the kick drum on every quarter note, we could use the following code. Using startTime and quarterNoteTime, we can do the math to make our buffered audio play precisely when it’s needed. For our purposes, the buffered audio is either kick, snare, or hihat. Each time, we pass along an audio buffer and a time specification. To create a rhythm, we call the playSound function for each individual note. Var quarterNoteTime = 60 / tempo Create a Rhythm Var tempo = 120 // BPM (beats per minute) Var startTime = context.currentTime + 0.100 We'll start playing the rhythm 100 milliseconds from "now" This gives us the exact length of each quarter note no matter what the actual tempo is set to. We need to take the number of seconds in a minute (60) and divide by tempo. The quarterNoteTime variable is important and requires a bit of math. The actual tempo (in BPM or beats per minute) is assigned to the tempo variable. This will start playing the rhythm 100 milliseconds from the moment it is triggered, which gives the user just enough time to release the button that was clicked. The startTime variable is set to context.currentTime + 0.100. This function is passed the contents of bufferList and assigns previously buffered audio assets to the variables kick, snare, and hihat. The startPlayingRhythm1 function is where the real magic happens. The playSound function plays a specified buffered audio asset at a specified time. They can be thought of as the Play Rhythm and Play Sound functions. One will contain the programmed rhythm, and the other will be used to play each individual audio asset (or note) within the rhythm. In order to play a timed rhythmic pattern, we need to create two functions. Buffering the audio assets immediately upon page load will help prevent any possible delay when the user actually attempts to play a rhythm. Next, our three audio files are loaded into the buffer using the BufferLoader class. For all other browsers, the warning alert “Web Audio API is not supported in this browser” is displayed. This function defines context as the new AudioContext for compatible browsers. Then we’ll create a function named init that’s called when the page loads. The files will be simple kick, snare and hi-hat drum sounds.įirst, we declare the variables context and bufferLoader in the global scope. For this tutorial, we’ll create two different rhythms using the same three buffered audio files. While it’s not the easiest or quickest way to create your backing tracks, it is rewarding in it’s own way. One of my favorite things about programming music is the moment of fruition when I finally hear what was, until that moment, only in my head. With the help of the Web Audio API, musical rhythms can be programmed in JavaScript and executed on the fly in your browser. Once you’re up to speed, you should be able to follow along as I explain how to create and play timed rhythms with Web Audio API and JavaScript. Before you tackle this, you should have a solid understanding of the Web Audio API. It builds on what we’ve covered in previous tutorials Web Audio API Basics, Web Audio API Audio Buffer, Play a Sound with Web Audio API, and Web Audio API BufferLoader. Timed Rhythms with Web Audio API and JavaScript is a tutorial that details how to create rhythms by triggering buffered audio at specific time intervals.
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