What would you call a sound with a frequency that varies over time?

A sound with a frequency that varies over time is known as noise. Noise is characterized by its chaotic and random nature, making it difficult to identify any specific frequency. This variability often leads to a sound that does not have a clear pitch, hence it differs significantly from tones or stable sounds, which maintain a consistent frequency over time.

In contrast, a stable sound is one that maintains a constant frequency, while a tone typically refers to a sound with a specific pitch that remains steady. Static sound can imply a lack of change or movement in frequency, which does not align with the definition of a sound whose frequency varies. Therefore, noise effectively encapsulates the idea of variability in sound frequency.