Which of these represents analog signal processing?

Analog signal processing involves manipulating signals that are represented in a continuous form, as opposed to discrete values used in digital signal processing. The option representing analog signal processing focuses on how signals can be mathematically altered or processed while retaining their analog nature.

Analog inverting specifically refers to a technique where an input analog signal is inverted, meaning its waveform is flipped around the horizontal axis. This is done using analog circuitry, such as operational amplifiers, which handle continuous signals without converting them into digital form. As a result, the integrity of the analog characteristic of the signal is maintained, and the processing can continue to be performed as part of an analog system.

Other options involve digital processes or specific analog techniques that may not represent the direct manipulation of continuous signals. For instance, digital filtering and digital modulation pertain to the processing of signals that have already been converted into digital form, while analog compression, although related to analog techniques, does not necessarily denote the basic process of analog signal manipulation but rather focuses on reducing the dynamic range of an analog signal. Thus, the focus of the correct answer is entirely aligned with the essence of analog signal processing.