@audio/filter-preemphasis

Pre-emphasis / de-emphasis filter

npm install @audio/filter-preemphasis

import { emphasis, deemphasis } from '@audio/filter-preemphasis'

First-order highpass (emphasis) and its inverse (de-emphasis) — used before and after coding or transmission.

$H(z) = 1 - \alpha z^{-1}$ (emphasis)  /  $H(z) = \dfrac{1}{1 - \alpha z^{-1}}$ (de-emphasis)

Rolloff: emphasis boosts above $f_c = \frac{(1-\alpha) f_s}{2\pi}$ — $\alpha = 0.97$ gives ~210 Hz at 44.1 kHz Inverse pair: deemphasis exactly cancels emphasis — $H_e(z) \cdot H_d(z) = 1$ (round-trip error ~5.5e-17)

emphasis(buffer, { alpha: 0.97 })    // before encoding
deemphasis(buffer, { alpha: 0.97 })  // after decoding — exact inverse

| Function | Param | Default | | |---|---|---|---| | emphasis | alpha | 0.97 | GSM/AMR speech coding convention | | deemphasis | alpha | 0.97 | must match the emphasis call it inverts |

Pass the same params object on every call to persist the one-pole state across blocks.

Use when: speech coding (GSM, AMR uses $\alpha = 0.97$), tape recording, FM broadcasting.

Part of @audio/filter — the filter family umbrella. This README is generated from the umbrella docs.

MIT © audiojs