Understanding Digital Audio: Key Concepts and Terminology

Key Digital Audio Concepts Explained

Frequency

The number of vibrations per second that gives rise to analog sound. The sound spectrum is characterized by its frequency range, which is measured in Hertz (Hz). The human ear picks up only those sounds within the frequency range of 20 Hz to 20,000 Hz.

Sampling Rate (Sample Rate)

Digital audio is a sequence of zeros and ones obtained by sampling an analog signal. The sampling rate, or sample rate, defines how often the value of the analog signal is taken to generate digital audio. This rate is measured in Hertz (Hz). For example, 44,100 Hz indicates that in one second, 44,100 samples were taken from the analog audio signal to create the corresponding digital audio. Higher-quality audio will have a higher sampling rate. Some standard frequencies are 44,100 Hz, 22,050 Hz, and 11,025 Hz.

Resolution (Bit Resolution)

The number of bits used to store each sample of the analog signal. An 8-bit resolution provides 256 (2⁸) levels of spaciousness, while a 16-bit resolution reaches 65,536 (2¹⁶). Digital audio quality will be higher with a higher resolution. For example, CD-quality audio is usually a sound of 44,100 Hz, 16-bit, stereo.

Transmission Speed (Bitrate)

The bitrate defines how much physical space (in bits) a certain length of audio takes. For example, a 3-minute MP3 audio file at 128 kbps occupies 2.81 MB of physical space (3 min x 60 sec/min x 128 kBit/sec = 23,040 kbits -> 23,040 kbps x 1024 bits/Kbit / 8 bits/byte / 1024 bytes/Kbyte / 1024 Kbytes/Mbyte = 2.81 MBytes or MB). For example, the MP3 audio format often works with bitrates of 128 kbps (kilobits per second). Audio quality will be higher with a higher bitrate, and the file containing it will have a larger size. This metric is mainly used in the MP3 audio format for internet downloads.

CBR / VBR

Constant / Variable Bitrate. CBR indicates that the audio has been encoded to maintain a constant bitrate throughout the audio clip, while VBR varies between a maximum and minimum range in terms of transfer rate.

Codec

An acronym for encoding / decoding. A codec is an algorithm that limits the number of bytes an audio file occupies. Files encoded with a specific codec require the same codec to be decoded and reproduced. The most widely used audio codec is MP3.

Decibel

A unit of measurement for the volume or intensity of a sound. Silence, or the absence of sound, is quantified as 0 dB, and the pain threshold for human hearing is around 130 to 140 dB.