How often the waveform is sampled each second is called the samplerate. The value sampled at the snapshot time is a digital number representing the volume at that time. An audio CD, for example, is sampled at the frequency of 44,100 times per second, which is traditionally identified as 44.1kHz. A sample is nothing more than a snapshot of a waveform sampled at fixed intervals. A typical waveform from Adobe Audition CC 2014įor any sound to be digitized, like a color image in Fireworks or Photoshop, the wave needs to be sampled. The horizontal line is time, and if the signal doesn’t leave the horizontal line, that’s silence.įigure 6-1. These waves, an example is shown inFigure 6-1, are called the waveform. As for the height of the waves, that’s called the amplitude of the signal, and the higher the wave, the louder the sound. We traditionally visualize sound as a sine wave-the closer together the waves, the higher the frequency and therefore the sound. Note W3C Audio Working Group has also developed a Web MIDI API specification (but it is currently only available as a trial implementation by Google Chrome, so we won’t explain this API at this time.īefore we start it would be useful to review the basics of digital audio. Mozilla used to implement a simpler audio processing specification called the “Audio Data API” but has since replaced this also with the Web Audio API specification. Safari is using a webkit prefix in its implementation at this point in time. Microsoft has added it to its development roadmap, so we can assume universal support. This specification has been implemented in all major desktop browsers except for Internet Explorer (IE). The Web Audio API () is a specification that is being developed by the W3C Audio Working Group. It also enables the visualization of audio data and the analysis of the data, for example, to determine a beat or identify which instruments are playing or whether a voice you are hearing is female or male. This enables the development of sophisticated web-based games or audio production applications where the audio can be dynamically created and modified in JavaScript. The Web Audio API (Application Programming Interface) complements the features we just learned about for manipulating video data. And that brings us to the subject of this chapter: how to manipulate sound data in a web browser. To do this one needs to stop regarding audio as sound and see it for what it really is: data that can be manipulated. The key aspect of audio is that when it is digitized it can be manipulated. From the simple effects such as click sounds that act as user feedback to voice-over narrations describing products or events, audio is a major communication medium which, as one of the authors likes to say, “seals the deal.” This is not to denigrate audio, but, in many respects, audio is treated as either an afterthought or an annoyance. When it comes to the Web, audio is.‘well’.it is just there. Manipulating Audio Through the Web Audio API Make the most of the new video and audio standards for the Web (2015) CHAPTER 6
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