Overtone - Realistic AI Offline Text to Speech (TTS)

Overtone is an offline Text-to-Speech asset for Unity. Enrich your game with 15+ languages, 900+ English voices, rapid performance, and cross-platform support.

Getting Started

Welcome to the Overtone documentation! In this section, we’ll walk you through the initial steps to start using the tools. We will explain the various features of Overtone, how to set it up, and provide guidance on using the different models for text to speech


Overtone provides a versatile text-to-speech solution, supporting over 15 languages to cater to a diverse user base. It is important to note that the quality of each model varies, which in turn affects the voice output. Overtone offers four quality variations: X-LOW, LOW, MEDIUM, and HIGH, allowing users to choose the one that best fits their needs.

The plugin includes a default English-only model, called LibriTTS, which boasts a selection of more than 900 distinct voices, readily available for use. As lower quality models are faster to process, they are particularly well-suited for mobile devices, where speed and efficiency are crucial.

How to download models

The TTSVoice component provides a convenient interface for downloading the models with just a click. Alternatively you can open the window from Window > Overtone > Download Manager


The plugin contains a demos to demonstrate the functionality: Text to speech. You can input text, select a downloaded voice in the TTSVoice component an listen to it



This class loads and setups the model into memory. It should be added into scenes that Overtone is planned to be used. It exposes 1 method, Speak which receives a string and a TTSVoice and returns an audioclip.

public async Task<AudioClip> Speak(string text, TTSVoiceNative voice)

Example programatic usage:

string text = "Hello World!";
TTSVoiceNative voice = TTSVoiceNative.LoadVoiceFromResources("en-us-ryan-high");
AudioClip audioClip = await Engine.Speak(text, Voice.VoiceModel);
source.clip = audioClip;
source.loop = false;



This script loads a voice model and frees it when necessary. It also allows the user to select the speaker id to use in the voice model.

Script Reference for TTSVoice.cs

Property Type Description Default Value
speakerId int The speaker id to be used 0
voiceName string The model to use libritts


TTSPlayer.cs is a script that combines a TTSVoice and a TTSEngine into synthesized text.

Script Reference for TTSPlayer.cs

Property Type Description Default Value
Engine TTSEngine The TTSEngine to use null
Voice TTSVoice The voice model to use null
Source AudioSource The source where to output the generated audio null


SSMLPreprocessor.cs is a static class that offers limited SSML (Speech Synthesis Markup Language) support for Overtone. Currently, this class supports preprocessing for the <break> tag.

Speech Synthesis Markup Language (SSML) is an XML-based markup language that provides a standard way to control various aspects of synthesized speech output, including pronunciation, volume, pitch, and speed.

While we plan to add partial SSML support in future updates, for now, the SSMLPreprocessor class only recognizes the <break> tag.

The <break> tag allows you to add a pause in the synthesized speech output.

Supported Platforms

Overtone supports the following platforms:

Platform Supported

If interested in any other platforms, please reach out.

Supported Languages

Language Best Quality Number of Voices
Català (Espanya) (ca-es) MEDIUM 3
Čeština (Česká Republika) (cs-cz) MEDIUM 1
Dansk (Danmark) (da-dk) MEDIUM 1
Deutsch (Deutschland) (de-de) HIGH 16
Ελληνικά (Ελλάδα) (el-gr) LOW 1
English (United Kingdom) (en-gb) MEDIUM 131
English (United States) (en-us) HIGH 958
Español (España) (es-es) MEDIUM 6
Español (México) (es-mx) MEDIUM 1
Suomi (Suomi) (fi-fi) MEDIUM 2
Français (France) (fr-fr) MEDIUM 6
Magyar (Magyarország) (hu-hu) MEDIUM 2
Íslenska (Ísland) (is-is) MEDIUM 4
Italiano (Italia) (it-it) X-LOW 1
ქართული (საქართველო) (ka-ge) MEDIUM 1
Қазақ Тілі (Қазақстан) (kk-kz) HIGH 8
Lëtzebuergesch (Lëtzebuerg) (lb-lu) MEDIUM 1
नेपाली (नेपाल) (ne-np) MEDIUM 36
Nederlands (België) (nl-be) MEDIUM 4
Nederlands (Nederland) (nl-nl) LOW 2
Norsk (no-no) MEDIUM 1
Polski (Polska) (pl-pl) MEDIUM 3
Português (Brasil) (pt-br) MEDIUM 2
Português (Portugal) (pt-pt) MEDIUM 1
Română (România) (ro-ro) MEDIUM 1
Русский (Россия) (ru-ru) MEDIUM 4
Slovenčina (Slovensko) (sk-sk) MEDIUM 1
Српски (sr-rs) MEDIUM 2
Svenska (Sverige) (sv-se) MEDIUM 1
Kiswahili (sw-cd) MEDIUM 1
Türkçe (Türkiye) (tr-tr) MEDIUM 2
Українська (Україна) (uk-ua) MEDIUM 4
Tiếng Việt (Việt Nam) (vi-vn) MEDIUM 67
中文 (中国) (zh-cn) MEDIUM 2


For any questions, issues or feature requests don’t hesitate to email us at help@leastsquares.io or join the discord. Very are happy to help and aim to have very fast response times :)

About us

We are a small company focused on building tools for game developers. Send us an email to careers@leastsquares.io if interested in working with us. For any other inquiries, feel free to contact us at hello@leastsquares.io or contact us on the discord

Sign up to our newsletter.

Want to receive news about discounts, new products and updates?