Before you start working on a project you should decide what sampling rate you’re going to be working with. This can be a complicated decision. One thing to consider is the final delivery of your sound. If, for example, you plan to publish this content only as an audio CD, then you might choose to work with a 44,100 Hz sampling rate to begin with since that’s the required sampling rate for an audio CD. If you plan to publish your content to multiple formats, you might choose to work at a higher sampling rate and then convert down to the rate required by each different output format.
The sampling rate you use is directly related to the range of frequencies you can sample. With a sampling rate of 44,100 Hz, the highest frequency you can sample is 22,050 Hz. But if 20,000 Hz is the upper limit of human hearing, why would you ever need to sample a frequency higher than that? And why do we have digital systems able to work at sampling rates as high as 192,000 Hz?
First of all, the 20,000 Hz upper limit of human hearing is an average statistic. Some people can hear frequencies higher than 20 kHz, and others stop hearing frequencies after 16 kHz. The people who can actually hear 22 kHz might appreciate having that frequency included in the recording. It is, however, a fact that there isn’t a human being alive who can hear 96 kHz, so why would you need a 192 kHz sampling rate?
Perhaps we’re not always interested in the range of human hearing. A scientist who is studying bats, for example, may not be able to hear the high frequency sounds the bats make but may need to capture those sounds digitally to analyze them. We also know that musical instruments generate harmonic frequencies much higher than 20 kHz. Even though you can’t consciously hear those harmonics, their presence may have some impact on the harmonics you can hear. This might explain why someone with well-trained ears can hear the difference between a recording sampled at 44.1 kHz and the same recording sampled at 192 kHz.
The catch with recording at those higher sampling rates is that you need equipment capable of capturing frequencies that high. Most microphones don’t pick up much above 22 kHz, so running the signal from one of those microphones into a 96 kHz ADC isn’t going to give you any of the frequency benefits of that higher sampling rate. If you’re willing to spend more money, you can get a microphone that can handle frequencies as high at 140 kHz. Then you need to make sure that every further device handling the audio signal is capable of working with and delivering frequencies that high.
If you don’t need the benefits of sampling higher frequencies, the other reason you might choose a higher sampling rate is to reduce the latency of your digital audio system, as is discussed in Section 5.2.3.
A disadvantage to consider is that higher sampling rates mean more audio data, and therefore larger file sizes. Whatever your reasons for choosing a sampling rate, the important thing to remember is that you need to stick to that sampling rate for every audio file and every piece of equipment in your signal chain. Working with multiple sampling rates at the same time can cause a lot of problems.