Web Audio API

Web Audio API
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Loading sounds

For example, if we want to pause a sound and play it back from the paused position, we can implement a pause by tracking the amount of time a sound has been playing in the current session and also tracking the last offset in order to resume later:. To play back the underlying buffer again, you need to create a new source node AudioBufferSourceNode and call start :.

Though recreating the source node may seem inefficient at first, keep in mind that source nodes are heavily optimized for this pattern.

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By having this AudioBuffer around, you have a clean separation between buffer and player, and can easily play back multiple versions of the same buffer overlapping in time. If you find yourself needing to repeat this pattern, encapsulate playback with a simple helper function like playSound buffer in an earlier code snippet. Assuming we have already loaded the kick, snare, and hihat buffers, the code to do this is simple:.

A good way of dealing with this problem is to create your own scheduler using JavaScript timers and an event queue. This approach is described in A Tale of Two Clocks. Many types of audio nodes have configurable parameters. For example, the GainNode has a gain parameter that controls the gain multiplier for all sounds going through the node.

Specifically, a gain of 1 does not affect the amplitude, 0. The values of these nodes can be changed directly by setting the value attribute of a param instance:. The values can also be changed later, via precisely scheduled parameter changes in the future. We could also use setTimeout to do this scheduling, but this is not precise for several reasons:. The main JS thread may be busy with high-priority tasks like page layout, garbage collection, and callbacks from other APIs, which delays timers. The JS timer is affected by tab state.

For example, interval timers in backgrounded tabs fire more slowly than if the tab is in the foreground.

About AudioContext

When we do it this way, we have to pass in the context and any options that that particular node may take:. Processing live audio input using a MediaStream from getUserMedia. It forms a compound parameter with frequency to form the computedOscFrequency. Maybe for example where via the Web Audio API you could load in multiple sources and then have a native global event that would start all those tracks simultaneously. The next step to get it working again would be: sourceNode. Set the rendering thread state to suspended.

Instead of setting the value directly, we can call the setValueAtTime function, which takes a value and a start time as arguments. For example, the following snippet sets the gain value of a GainNode in one second:. In many cases, rather than changing a parameter abruptly, you would prefer a more gradual change. For example, when building a music player application, we want to fade the current track out, and fade the new one in, to avoid a jarring transition.

A basic guide to the Web Audio API

While you can achieve this with multiple calls to setValueAtTime as described previously, this is inconvenient. The difference between these two lies in the way the transition happens. In some cases, an exponential transition makes more sense, since we perceive many aspects of sound in an exponential manner. Given a playlist, we can transition between tracks by scheduling a gain decrease on the currently playing track, and a gain increase on the next one, both slightly before the current track finishes playing:.

If neither a linear nor an exponential curve satisfies your needs, you can also specify your own value curve via an array of values using the setValueCurveAtTime function.

What Is the Web Audio API? (Learn Web Audio from the Ground Up, Part 0)

With this function, you can define a custom timing curve by providing an array of timing values. It took a bit of math, though. This brings us to a very nifty feature of the Web Audio API that lets us build effects like tremolo more easily.

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  • A basic guide to the Web Audio API.

We can take any audio stream that would ordinarily be connected into another AudioNode , and instead connect it into any AudioParam. This important idea is the basis for many sound effects.

Making the Web Rock: The Web Audio API

The previous code is actually an example of such an effect called a low frequency oscillator LFO applied to the gain, which is used to build effects such as vibrato, phasing, and tremolo. It is worth noting, however, that an audio element can be used as the source for an Web Audio Context — we may delve more into this in the future.

Table of Contents

Then, we declare an async function. We await the response from fetch, and then get the response body as an array buffer and return it. Then, in play , we perform both the loading and playing, so our api becomes just a call to play with the file location and wait on the promise returned from our async load function.

Except… if you do this with your meow. The file will successfully be fetched, loaded, decoded… but not played. So, most browsers have various autoplay policies which restrict what the page can do with media before the user has interacted with it. Oh, and it would be nice not to need to re-download a file every time we want to play it if we anticipate needing to play it multiple times.

Hello Web Audio API

Now, when we load our meow. Then, in load , we also perform the decoding, falling back to a decode shim if the browser throws an error as it does in iOS , due to out-of-date API implementation.

Example code

Depending on the needs of your project, you may want to explore some of the libraries that can handle some of the grunt work for you, like Howler. The Meowsic machine project is on its way—next time, we prepare to begin working on the UI with Vue.


Jul 2, The Web Audio API provides a powerful and versatile system for controlling audio on the Web, allowing developers to choose audio sources. Jun 24, Let's take a look at getting started with the Web Audio API. We'll briefly look at some concepts, then study a simple boombox example that.

Images from Wikipedia Commons: cassette , padlock. Tags: audio javascript js web WebAudio. You are reminded that the universe can be a cruel place. AudioContext window.