What device provides a graphic display of energy versus frequency?

The spectrum analyzer is the device that provides a graphic display of energy versus frequency. It is specifically designed to analyze the frequency spectrum of signals, allowing users to visualize the amplitude (energy) of signals as they relate to their frequency components. This capability is essential in various applications, such as telecommunications, audio engineering, and electromagnetic spectrum analysis. By displaying this information graphically, engineers and technicians can identify the presence and levels of various frequencies in a signal, assess signal quality, and troubleshoot issues in electronic systems.

The other devices listed have different primary functions. A signal generator is used to produce electrical signals with specific properties, often for testing or calibration purposes, but does not provide a direct visual representation of energy versus frequency. A frequency modulator modulates the frequency of a carrier wave to encode information, but it does not analyze or display spectral content. A waveform converter processes and modifies waveforms but is not focused on providing a frequency spectrum display. Thus, the spectrum analyzer is uniquely suited for the task described in the question.