What Does the Unit kHz Mean in Digital Music?

kHz is short for kilohertz, and is a measurement of frequency (cycles per second). In digital audio, this measurement describes the number of data chunks used per second to represent an analog sound in digital form. These data chunks are known as the sampling rate or sampling frequency.

This definition is often confused with another popular term in digital audio, called bitrate (measured in kbps). However, the difference between these two terms is that bitrate measures how much is sampled every second (size of the chunks) rather than the number of chunks (frequency).

Note: kHz is sometimes referred to as sampling rate, sampling interval, or cycles per second.

In digital audio the most common sampling rates you'll encounter include:

• 8 kHz for speech, audiobooks, etc.
• 22 kHz for digitized analog mono recordings such as vinyl records and cassette tapes
• 32 kHz for streaming music, radio stations
• 44.1 kHz is used for audio CDs and typically the de facto standard for downloaded music (like from iTunes) in formats like MP3, AAC, WMA, and others
• 48 and 96 kHz is used for high definition equipment and professional audio

In theory, the higher the kHz value that is used, the better the sound quality will be. This is due to more data chunks used to describe the analog waveform.

This is normally true in the case of digital music which contains a complex mix of frequencies. However, this theory falls down when you are dealing with other types of analog sound like speech.

The popular sampling rate for speech is 8 kHz; way below audio CD quality at 44.1 kHz. This is because the human voice has a frequency range of approximately 0.3 to 3 kHz. With this example in mind, a higher kHz doesn't always mean better quality audio.

What's more is that as the frequency climbs to levels that most humans can't even hear (usually around 20 kHz), it's been suggested that even those inaudible frequencies can negatively affect the sound quality.

You can test this by listening to something at an ultra high frequency that your sound device supports but that you're not supposed to hear, and you might find that depending on your equipment, you'll actually hear clicks, whistles, and other sounds.

These sounds mean that the sampling rate is set too high. You can either buy different equipment that can support those frequencies or you reduce the sampling rate to something much more manageable, such as 44.1 kHz.