Speech spectrograms are derived using cochlear-scaled band partitioning following Greenwood spacing

Evidence

The spectrogram (Sgram) was obtained by partitioning the speech signal into three frequency-bands logarithmically spaced between 70 and 5000 Hz according to Greenwood’s equation (70–494–1680–5000 Hz, the same used for the vocoder), and computing the amplitude envelope for each band. — Dijk, Pim van, Physiology, Psychoacoustics and…, 4478

Categorization

• XREF: Greenwood’s equation implements cochlear place-frequency mapping — ties signal processing to physiological frequency resolution, central to the reader’s purpose.
• SHARE: The specific 70-494-1680-5000 Hz band edges following Greenwood spacing would interest an audio signal processing colleague.