Comparing Audio File Size to Quality

It's important to understand how audio is captured. The quality of the audio file is determined by its sample rate. With audio, digital audio (such as from DATs) is rated as the highest quality, recorded at 48 kHz, or 48,000 samples per second. These samples are "snapshots"of the audio signal. The higher the number, the more details about that source that are being recorded. The lower the number, the longer the time intervals are when your sound is sampled. This means that the computer basically fills in the intervals between samples, resulting in a less-accurate representation of the original source signal.

A good way to describe what takes place with the sample rate is to imagine a connect-the-dots game (see Figure 2.20). Notice the more-accurate definition between points over the course of 1 second. The more samples that are taken, the better-quality reproduction that signal has. Where is the cutoff? Well, that depends on you. The lower the sample rate, the smaller the file size. The higher the sample rate, the better the quality of the sound file. Each project you produce determines the individual specifications. I recommend that you always capture at the highest sample rate (the best quality). You can always convert it down (44 kHz to 11.025 kHz), but you can never go in the reverse direction. See Chapter 10, "Outputting Your Work," to find out more about output options and signal qualities available through Premiere.

Figure 2.20. Sample rate is similar to a connect-the-dots game. The higher the sample rate, the more accurate the detail it captures.

Other factors to be aware of when capturing audio are the bit depth settings and the stereo settings. Bit depth is the number of bits per sample. The two most common are 8-bit and 16-bit. Similar to sample rate, the higher the number, the better-quality sound file you will have. You can also choose to digitize your audio in mono or stereo. Stereo tracks create a sense of perception and space. This is usually created by having two tracks (as opposed to one track in mono) and panning one track to the left speaker and one to the right speaker. You have more control over panning your sound tracks to the left, center, or right. Having separate tracks also offers you more control over changing levels, pans, and other beneficial factors. But just like everything else in life, the better the quality, the larger the file size.

tip

Unless free hard drive space is absolutely at a minimum, always capture your audio at the highest quality. The highest-quality audio files are still only a fraction of the file size of the same length video clip.