Node.js

import { createEspeak } from "@spelling-creator/spellophone";
// or, explicitly:
import { createEspeak } from "@spelling-creator/spellophone/node";

createEspeak loads the wasm module and the core data, then returns an Espeak instance. Everything on the instance is synchronous after that.

Options

const espeak = await createEspeak({
  // Preload these dictionaries. Everything else still loads on demand.
  languages: ["en", "de"],
  // Emit a phoneme event per phoneme during synthesis: true or "ipa".
  phonemeEvents: "ipa",
  // Use a data directory other than the one in the package.
  data: "/srv/espeak-ng-data",
  // Use a wasm file other than the one in the package.
  wasm: "/srv/espeak-ng.wasm",
});

Dictionaries load on demand

espeak-ng needs a per-language dictionary before it can speak or transcribe a language. In Node.js these are read from disk, synchronously, the first time a voice asks for one, so setVoice("de") just works. languages lets you pay that cost at startup instead, and "all" preloads every language (about 19 MB of memory).

Writing audio files

encodeWav turns the samples into a WAV file, the same output espeak-ng -w produces:

import { writeFile } from "node:fs/promises";
import { createEspeak, encodeWav } from "@spelling-creator/spellophone";

const espeak = await createEspeak();
const { samples, sampleRate } = espeak.synthesize("Good morning.", {
  voice: "en-gb",
});
await writeFile("morning.wav", encodeWav(samples, sampleRate));

For other formats, hand the raw PCM to an encoder. The samples are signed 16-bit, mono, little-endian in memory, at espeak.sampleRate Hz.

Threads

An Espeak instance is synchronous and single-threaded, which is how espeak-ng itself works. Synthesis of a sentence takes a few milliseconds, so this is rarely a problem. If it is, create one instance per worker thread with node:worker_threads; instances do not share state.

Where the files live

The package ships three things the Node build reads at run time:

Path	Contents
wasm/espeak-ng.wasm	espeak-ng compiled to WebAssembly
wasm/espeak-ng.js	The Emscripten glue that loads it
espeak-ng-data/	The compiled data, gzipped, plus manifest.json

If you bundle a Node application, keep those files next to the bundle or point createEspeak at them with the data and wasm options.