Writing Sample: Digital Audio Primer

These frogs are creating audio samples—regular measurements of a sound wave's volume over time.

These frogs are creating audio samples—regular measurements of a sound wave’s volume over time.

Both high-tech professionals and lay people tend to confuse the terms and concepts of internet audio, which is digital in nature.
I used interactive Flash animation and an audio voice-over to demystify this highly technical subject and make it understandable to both geeks and non-geeks. The use of metaphorical characters—frogs—helped keep the topic light and fun. I’ve since delivered this presentation many times. Here’s an excerpt from my narrative:

How Is Digital Audio Produced?

To record a sound digitally, we must first create a numeric description of the sound wave. Remember that even the most complex sound is just a continuous variation in air pressure over the course of time. Keeping this in mind, we should be able to measure and record the amplitude of a sound at regular intervals in time, and then reconstruct the sound wave from our recorded data. Here’s an example of how that might work:

A microphone is used to generate a small electrical current whose strength varies with changes in air pressure. If we record the strength of the current frequently enough, we’ll be able to reconstruct the sound wave.

Here we measure a sound whose frequency is around 440 cycles per second. We’ll need to take numerous measurements during each cycle to accurately reconstruct the shape of the wave.  

In fact, to make a digital audio recording that is completely convincing to the ear, we must take measurements over 40,000  times per second. Each measurement is called a sample – we’re grabbing a sample of the air pressure at that moment. How often we take the measurements is known as the sample rate. Music CDs are recorded at a sample rate of 44,100 times per second, or 44.1 kiloHertz.

As you can imagine, it’s not simple to record 44.1 thousand numbers in a single second, and it can result in huge data files.