Which of the following is TRUE of a decibel?

A decibel is indeed defined as a ratio of two numbers used to express the difference or change in a specific measurement, often relating to power or intensity. In the context of audiovisual technology, the decibel scale is commonly applied to measures of sound and signal levels. It allows for a logarithmic way to represent large ranges of values in a more manageable format, making it easier to understand significant changes in sound level or electrical signals.

This definition underscores why option D is the correct statement. By using the decibel scale, professionals can compare the intensity of sounds or signal strengths relative to a reference level. The ability to express ratios in this manner is foundational for many applications in audio, broadcasting, and electronic measurement.

The other options are based on aspects of how decibels relate to sound and power but do not accurately capture the broad definition of what a decibel is. For example, while certain logarithmic functions relate specifically to power and sound pressure levels, they do not encompass the full definition of a decibel. Therefore, the assertion that a decibel is fundamentally a ratio effectively communicates the core concept of what decibels represent in various technical fields.