What defines a sub-harmonic frequency?

A sub-harmonic frequency is indeed characterized by having a frequency that is a submultiple of another sine wave frequency. This means that if you take a primary frequency, the sub-harmonic frequency can be represented as an integer division of that primary frequency. For example, if the primary frequency is 100 Hz, then a sub-harmonic frequency could be 50 Hz (which is 100 Hz divided by 2) or 33.33 Hz (which is 100 Hz divided by 3). This concept is crucial in various fields, such as signal processing and sound engineering, where understanding the relationship between harmonics and sub-harmonics helps in analyzing waveforms and their interactions.

In this context, the other options do not accurately describe sub-harmonic frequencies. Defining it as an independent frequency does not capture the relationship it has with a primary frequency, while stating it as a multiple of the primary frequency would describe harmonics rather than sub-harmonics. The aspect of generating noise interference pertains to undesirable effects in signal transmission and is not a defining characteristic of sub-harmonic frequencies, which are simply defined by their mathematical relationship with the primary frequency.