klattsch

A primitive parallel-formant speech synthesizer in the browser. Late-70s / early-80s tier (Votrax, SAM).

The name is a portmanteau of Klatt (Dennis Klatt, the formant-synth pioneer) and Klatsch (German for gossip / casual chat).

Live demo

Commercial support - integration consulting from the author

What it does

You type a phoneme string in ARPABET, with optional directives, and the computer says it.

HH AH L OW                        hello, default voice
b140 HH AH L OW                   higher voice
bA3 HH AH L OW                    higher voice (note name)
AY+15 D IH D                      "I did" with a rising contour
D IH D DH AE(+40) T               "did THAT" with a transient pitch ornament on AE
r200 bC#4 ( HH AH ) ( L OW )      sung syllables, one note per group

See the in-app syntax help panel for the full directive table.

Installation

npm install klattsch

The same package works as a CLI, as an importable engine in Node, and as an embeddable engine + AudioWorklet in the browser. Zero runtime dependencies.

Usage

CLI

Render a phoneme string straight to a WAV file:

npx klattsch "HH AH L OW" hello.wav

Node / OfflineAudioContext

import { compileString, FormantSynth, encodeWav } from 'klattsch';

const sampleRate = 48000;
const { schedule, totalMs } = compileString('HH AH L OW');
const synth = new FormantSynth({ sampleRate, schedule });
const buf = new Float32Array(Math.ceil(totalMs * sampleRate / 1000));
synth.process(buf);

const { bytes } = encodeWav(buf, sampleRate);
// write bytes to a .wav file

Browser with a bundler (Vite, webpack, esbuild, Rollup)

import { compileString } from 'klattsch';
import workletUrl from 'klattsch/formant-worklet.js?url';

const ctx = new AudioContext();
await ctx.audioWorklet.addModule(workletUrl);
const node = new AudioWorkletNode(ctx, 'formant-processor');
node.connect(ctx.destination);

const { schedule } = compileString('HH AH L OW');
node.port.postMessage({ type: 'schedule', schedule });

Browser without a bundler (CDN)

<script type="module">
  import { compileString } from 'https://esm.sh/klattsch';

  const ctx = new AudioContext();
  await ctx.audioWorklet.addModule('https://esm.sh/klattsch/formant-worklet.js');
  const node = new AudioWorkletNode(ctx, 'formant-processor');
  node.connect(ctx.destination);

  const { schedule } = compileString('HH AH L OW');
  node.port.postMessage({ type: 'schedule', schedule });
</script>

How it works

• Excitation: voiced source is a Rosenberg-style glottal pulse with a tunable open / closed quotient (g / "effort") and unvoiced source is xorshift noise. These are crossfaded by each phoneme's voicing parameter, with optional aspiration noise mixed in.
• Filtering: three parallel bandpass biquads for each formant.
• Prosody: the sequencer compiles phoneme strings into a time-stamped schedule of formant targets.
• Voice character: vibrato (depth + rate), aspiration / breathiness, spectral tilt, and glottal effort are all controllable.

References

• Klatt, D. H. (1980). Software for a cascade/parallel formant synthesizer.
• Hillenbrand et al. (1995). Acoustic characteristics of American English vowels.
• Rosenberg, A. E. (1971). Effect of glottal pulse shape on the quality of natural vowels.
• Robinson, R. Bristow-Johnson. Audio EQ Cookbook.
• Mokhtari, P. & Tanaka, K. (2000). A Corpus of Japanese Vowel Formant Patterns. Bulletin of the Electrotechnical Laboratory (ETL), Vol. 64, Special Issue, 57-66. (project page, data file) - source of the Japanese vowel formants in the ja-mokhtari-2000 phoneme bank.

See also

• libadlmidi-js - WebAssembly build of libADLMIDI, an OPL3 FM synthesis library with AudioWorklet integration. Where klattsch does parallel-formant vocal-tract synthesis, libadlmidi-js does FM-operator synthesis: the sound of early-80s arcade boards and AdLib cards. Includes oplsfxr, a sfxr-style sound effect generator.

Built with klattsch

• klattsch-sing - a piano-roll sequencer for speech-based singing synthesis. Draw notes, type words or phonemes, render to WAV. Supports MIDI import, quantization, tempo + time signature, demo songs, and a custom KSP project file format. Built on the klattsch npm package.

Commercial Support

klattsch is built and maintained by Tony Gies. For studios, indie developers, and agencies integrating klattsch into a shipped product, consulting is available through his consultancy, Crash United, LLC.

Support Offerings

| Service | Description | |---------|-------------| | Game / app integration | Wiring klattsch into your engine (Unity, Godot, web, Electron, Flutter), with dialog-system glue and tooling for non-programmer collaborators (writers, sound designers) | | Custom character voices | Crafting a recognizable voice signature for a specific character: formant tuning, prosody templates, phoneme calibration, voice tests against scripted dialogue | | Audio pipeline work | Routing klattsch through your DSP graph: mixing with music, ducking, environmental effects (reverb, distortion, radio filtering), multi-voice ensembles, dynamic vocal sizing | | Language / phoneme expansion | Non-English phoneme tables, alternate transcription formats, custom symbol sets for stylized worlds (alien races, fantasy languages, in-universe scripts) | | Performance tuning | Real-time constraints (game audio thread, low-latency targets), WASM/Rust ports, embedded or constrained-runtime targets | | Custom DSP features | Cascade synthesis, additional formants, LPC pre-filtering, vocoder modes, custom synth extensions beyond the included parallel-resonator engine | | Priority bug fixes | Reported issues triaged and patched ahead of the public queue, with backports to your pinned version | | Workshops / talks | Formant synthesis, retro speech tech, or DSP fundamentals for your team |

For pricing, scoping, or anything not listed above, email [email protected] to discuss your project.

Sponsorship

To support ongoing development without a formal contract, GitHub Sponsors or Ko-fi are the simplest paths.

License

MIT © Tony Gies