What process do audio PCM encoders use to accommodate the sensitivity of the human ear to sound levels?

The correct answer is log-based companding. This process is specifically designed to adapt to the human ear's varying sensitivity to different sound levels. The human ear does not perceive sound in a linear fashion; it is more sensitive to changes in quieter sounds compared to louder sounds. Logarithmic companding applies a nonlinear transformation to audio signals, compressing the dynamic range and reducing the volume of the louder sounds while expanding the quieter sounds. This allows for more efficient use of the available dynamic range and helps to preserve audio quality, especially in systems that handle a wide range of sound levels.

In contrast, linear compression would not effectively accommodate the logarithmic nature of human hearing sensitivity, as it treats all levels of sound uniformly. Amplification simply increases the power of a signal without considering the nuances of how we perceive different sound levels. Harmonic encoding focuses on representing the audio in a way that emphasizes certain frequencies but does not specifically address dynamic range adjustments based on human auditory sensitivity. Thus, logarithmic companding is the best choice for addressing the sensitivity of the human ear in audio PCM encoding.