[Free & Paid] Speech Synthesis Engines: Which Software Uses Which?

Currently, many text-to-speech software programs have been released.

However, when listening to the audio from text-to-speech software, you might think, "Wait, isn't this voice tone the same as other software?"

Actually, text-to-speech software requires a base speech synthesis engine.

Therefore, even if the software names are different, if the speech synthesis engine is the same, the voice tone will be the same.

This time, we will introduce speech synthesis engines that can be used for free and those that can be used for a fee.

Including information that might make you think, "Oh, that software was using this synthesis engine!"

Please take a look!

Speech synthesis engines that can be used for free

Free text-to-speech software mainly uses:

• AquesTalk
• Open JTalk

these speech synthesis libraries and speech engines.

AquesTalk

Developed by AQUEST Co., Ltd., AquesTalk is known for "Yukkuri Voice" and "Bouyomi Voice."

All software capable of reading in the voice tone commonly referred to as "Yukkuri" employs "AquesTalk."

Representative examples include Bouyomi-chan and SofTalk.

Since synthetic voices can be easily created from text, it is used in various situations from personal use to commercial products.
In addition to being used as a base for SofTalk and Bouyomi-chan, it is also used for sampling in UTAU's default voice. Furthermore, it is used as the guidance voice for household appliances such as telephones.

AquesTalk was first released on May 25, 2006. The development period was said to be just under two years. (AquesTalk releaseexit)
The sound source is not recorded but created by manually manipulating parameters; it is a pure synthetic voice with no person "inside."

In January 2010, the successor version of AquesTalk, AquesTalk2exit was announced.
It supports a wide range of platforms including Windows, Mac OS X, WinCE, iPhone, Android, and other smartphones. Recently, even an independent microchip (hardware) called AquesTalk pico has appeared.

Source: Nico Nico Pedia

Because API usage licenses and development libraries are provided, it can be used for various purposes if you have programming skills.

Check the company website for details.

AquestTalk

Yukkuri Voice is also explained in this article.

【2026 Latest】6 Recommended Yukkuri Voice/Bouyomi Software | Complete Comparison of PC and Smartphone Apps

Introducing carefully selected Yukkuri Voice and Bouyomi software ideal for video production and game commentary. From PC to smartphone, we explain how anyone can easily create high-quality audio with the latest 2026 apps.

Open JTalk

Open JTalk is a Japanese text-to-speech synthesis system developed by the Tokuda/Lee Laboratory at the Nagoya Institute of Technology.

It is open source, distributed under the Modified BSD License.

"Open JTalk" is used in Textalk. Once you hear it, you might feel like you've heard it before.

Open JTalk

Speech synthesis engines that can be used for a fee

Paid speech synthesis engines include:

• IBM: Watson Text to Speech
• Google: Text to Speech
• Amazon: Polly
• Microsoft: SAPI5

There are many attractive plans, such as several tens of thousands of characters for free.

The paid speech synthesis engines mentioned above provide demos on their websites, where you can play and listen to the audio.

Speech synthesis engines have a high difficulty level

In this article, we introduced speech synthesis engines.

By using a speech synthesis engine, you can create your own text-to-speech software or finish it as text-to-speech software customized to your liking.

However, when trying to actually use them, since they are provided as APIs, setup is difficult without programming skills.

API stands for "Application Programming Interface," and it refers to "programs specialized for a certain function that can be shared" or "a mechanism for sharing software functions." If frequently used functions are prepared as APIs, there is no need to build a program from scratch. You can proceed with development efficiently by using APIs as needed.

In the case of Web APIs, programs are published on the web and utilized by calling them from the outside. Web APIs are published in various fields, and many Web APIs are available for free.

For example, if you can get the latest information from other sites via an API, you can add new functions to your own website or app and improve your service. In recent years, as the level required for smartphone apps has increased, it has become common to use Web APIs in app development.

Source: internet academy

Companies that provide paid versions of text-to-speech software either develop their own speech synthesis engines or use the paid speech synthesis engines introduced here.

"Why don't I just make a speech synthesis engine myself?"

You might think so, but this is not an easy task.

It would be a task requiring a difficult process involving many researchers, developers, and money.

At the very least, it is difficult for an individual and is not realistic unless you have the scale of a company or a research institution.

Therefore, if you find using an API difficult, using paid text-to-speech software is more intuitive and easier to handle.

Many types of text-to-speech software, from free to paid, have been released.

I am sure you will find your favorite software.

Since they are summarized in detail in this article, please check it out!

【2026 Latest】10 Recommended Text-to-Speech Software! Including Free Software for Commercial Use

Compare recommended text-to-speech software! Carefully introducing everything from browser-based tools that don't require installation to high-performance desktop types, including free tools available for commercial use.

I hope this article is helpful to you.

I look forward to seeing you again.