Module 6. The technical foundations of digital audio

Representing and storing audio digitally

Just like text and images, sound can be represented and stored digitally. However, digitally representing and storing sound is slightly more complex than storing images or text, in part because sound is temporal (that is to say, it unfolds through time) and because of the near-infinite variety of sounds that we can hear ( compared to the limited number of characters in any one alphabet or writing system).

Audio compression

In Activity 6.1, you may have noticed that the example of a 74-minute long sound file would need close to 747,000,000 bytes if you were to store it in its raw form. That's around three hundred seventy-four 2Gb USB flash drives! If you were interested in serving the sound file over the Web, that's still a lot of data to push over even in today's terms, so we often have to compress audio data.

Compression allows you to minimize the amount of data that it takes to represent digital audio. The most common type of compression uses perceptual coding, which makes an assumption about what average human beings cannot hear and eliminates it from the sound file. For example, very high-pitched and very low-pitched sounds could be discarded, as well as very soft sounds that follow right after very loud sounds. MP3 is an example of an audio format that uses perceptual coding.

Audio file formats

When saving a sound file after creating and editing it in your audio software, you will probably have the option of saving it in any of several file formats. Some popular file formats are WAVE (.wav), MP3 (.mp3), and Ogg Vorbis (.ogg). MP3 is by far the most popular format, but it is actually a proprietary format. Ogg is open source, but is not widely supported. You can learn more about audio file formats in a concise summary provided by an audio software company, NCH, on http://www.nch.com.au/acm/formats.html.

Manipulating sound

Because sound can be represented as waves that can be stored digitally as sequence of bits, you can not only change how an audio file sounds by manipulating the various features of the wave, but you can even create your own sounds. We will not cover sound manipulation and creation in this course, but you may learn more about it in the Audio in Multimedia course, MMS 172.

Summary

This module provided you a rough overview of the technical considerations related to recording, storing, and playing back digital audio.

While you may think that our sense of sight is more important than our sense of hearing, humans are actually very sensitive to sound. For example, studies have shown that when people are having a videoconference call over a poor connection, people are more tolerant of errors in the image quality than with errors in the sound. That is to say, people will often find dropped audio more displeasing and annoying that dropped visual information. In addition, recorded sound can have effects on people that analog or live sound may not be able to induce. You will learn about some unusual and powerful examples that illustrate the power of sound on people in Unit 3.