Often, it measures the power spectrum.
- An analogue spectrum analyzer uses either a variable bandpass filter whose mid-frequency is automatically tuned (shifted, swept) through the range of frequencies of which the spectrum is to be measured or a superheterodyne receiver where the local oscillator is swept through a range of frequencies.
- A digital spectrum analyzer uses the Fast Fourier Transform (FFT), a mathematical process that transforms a waveform into its frequency components in the spectrum. As a result, computer programs can compute such transforms, and makes audio processing easier. FFTs have applications in much wider fields.
Non-electronic spectrum analyzers
Used to measure atomic particles.