Publisher Summary This chapter focuses on the techniques used to probe spectral processing in auditory cortex, and proposes a rather simple model for how auditory cortex might be able to achieve fast multi-spectral scale analysis. While pure tones and AM sounds have proved to be useful stimuli for studying the auditory system, a better understanding of the need to separately define spectral processing can be seen by using a natural stimulus. The chapter also explains the different methods of measuring spectral processing including linear versus nonlinear spectral processing; the frequency response area (FRA) and frequency tuning curve (FTC); and two-tone FRAs, inhibitory response areas, and non-linear processing. The chapter presents a physiological explanation of how the auditory cortex might analyze and represent multiple frequency scales in parallel, and also focuses on experiments using narrow-band stimuli such as tones. The techniques using broad-band stimuli have been used to characterize spectral receptive fields (RFs) and spectral temporal receptive fields (STRFs). An advantage of using broadband stimuli is that if there are interactions across frequency (such as special properties for across-channel processing), then broad-band stimuli have energy spanning these potential interactions.