Tones

Tones are provided on recorded media – video, audio, analog, and digital – to establish a reference for playback levels and frequency response. While pink noise, sounding like static and containing a full range of frequencies, is commonly used as a frequency response reference, tones are sine waves recorded at varying, specific frequencies. 1kHz and 400Hz are common tones for level reference, with the addition of 10kHz and 100Hz tones for high and low frequency response.

An engineer typically records tones at the same time as the program material so that both tones and program reflect the same technical environment. Dolby® A tone and Dolby® SR noise are proprietary reference signals for Dolby noise reduction.

Common tones recorded prior to program are used as reference for playback levels and frequency response.