Frequency spectrum
A map of a sound from bass to treble, showing which frequencies carry the voice, rumble, hum, hiss, and everything between.
See it
What it is
A frequency spectrum shows how a sound's energy is distributed from low to high frequencies. A spectrum analyzer puts frequency in hertz across the horizontal axis and level in decibels on the vertical axis, exposing the fundamental, harmonics, broadband noise, and narrow tones that one waveform view piles together. Human hearing covers roughly 20 Hz to 20 kHz, and the top of that range shortens with age.
Reach for it when the ear says rumble, hum, mud, harshness, or hiss but you need to locate the band. A narrow spike at 50 or 60 Hz and matching multiples points toward mains hum; a heap below 80 Hz may be handling rumble; strong energy around 6 to 8 kHz can explain biting sibilance. A spectrogram adds time, showing when those frequencies appear. Voxengo SPAN is the free analyzer most people start with, and the spectrogram in iZotope RX is how dialogue editors spot a chair creak by eye before they ever hear it.
Gotcha: the graph is evidence, not an EQ prescription. Healthy voices and instruments overlap across wide bands, and the tallest visible peak is not automatically a problem. FFT size also trades time detail for frequency detail, so confirm any suspicious band by listening before cutting it.
Ask AI for it
Open this recording in Audacity and run Analyze > Plot Spectrum with the Spectrum algorithm, a Hann window, and FFT Size 4096. Report the five strongest frequency regions in hertz and dB, check specifically for 50 or 60 Hz hum and harmonics, sub-80 Hz rumble, and 6 to 8 kHz sibilance, then verify every flagged region by listening before recommending EQ.