Mimic 3
A fast, privacy-focused, open-source, neural Text to Speech (TTS) engine.
Mimic 3 is a neural text to speech engine that can run locally, even on low-end hardware like the Raspberry Pi 4. It is the default text to speech engine on the Mark II.

Installation

Hardware Requirements

Mimic 3 was designed to run on the Raspberry Pi 4 (64-bit OS), but will also run on other platforms:
  • amd64
    • AMD/Intel-based desktops/laptops
    • Tested:
      • Very fast on Ryzen 9 5950X, RTF less than 0.05
  • arm64
    • Raspberry Pi 3/4 and Zero 2 with 64-bit Pi OS
    • Tested:
      • Usable on Pi 4, RTF around 0.5
  • armv7l
    • Raspberry Pi 1/2/3/4 and Zero 2 with 32-bit Pi OS
    • Tested:
      • Slow on Pi 3, RTF around 1.3

Real-Time Factor

The performance of a text to speech system is often measured by its real-time factor (RTF). This is the ratio of how long it takes to generate audio to how long the audio is when spoken. In general, lower is better for RTF.
An RTF of 1 means that it took one second of compute time to generate one second of spoken audio. An RTF of 0.5 is better than 1, however, since the same second of spoken audio now only took half a second to generate.

Mycroft Devices

Device
Supported
Notes
Mark II
Full support
Default engine. Runs well locally.
Mark 1
Partial support
Runs slower than real-time because the Mark 1 contains a Raspberry Pi 3B. It is not recommended at this time.
Picroft
Variable
Varies depending on the hardware. A Raspberry Pi 4 or better is recommended.

Software Requirements

  • Linux
    • Recommended: 64-bit Debian bullseye or Raspberry Pi OS
  • Python 3.7+
    • Recommended: Python 3.9
  • Python packages
  • System packages
    • libespeak-ng1
    • libatomic1 (32-bit ARM only)
    • libgomp1 (32-bit ARM only)
    • libatlas-base-dev (32-bit ARM only)

TTS Plugin for Mycroft AI

Install the necessary system packages:
sudo apt-get install libespeak-ng1
On 32-bit ARM platforms (a.k.a. armv7l or armhf), you will also need some extra libraries:
sudo apt-get install libatomic1 libgomp1 libatlas-base-dev
Then, ensure that you're using the latest pip:
mycroft-pip install --upgrade pip
Next, install the TTS plugin in Mycroft:
mycroft-pip install mycroft-plugin-tts-mimic3[all]
Removing [all] will install support for English only.
Additional language support can be selectively installed by replacing all with a two-character language code, such as de (German) or fr (French). See setup.py for an up-to-date list of language codes.
Enable the plugin in your mycroft.conf file:
mycroft-config set tts.module mimic3_tts_plug
or you can manually add the following to mycroft.conf with mycroft-config edit user:
"tts": {
"module": "mimic3_tts_plug"
}
See the plugin's documentation for more options.

Docker Image

A pre-built Docker image is available for AMD/Intel CPUs as well as 32/64-bit ARM:
mkdir -p "${HOME}/.local/share/mycroft/mimic3"
chmod a+rwx "${HOME}/.local/share/mycroft/mimic3"
docker run \
-it \
-p 59125:59125 \
-v "${HOME}/.local/share/mycroft/mimic3:/home/mimic3/.local/share/mycroft/mimic3" \
'mycroftai/mimic3'
Visit the web page at http://localhost:59125
The following convenience scripts are also available:

Debian Package

Grab the Debian package from the latest release for your platform:
  • mycroft-mimic3-tts_<version>_amd64.deb
    • For desktops and laptops (AMD/Intel CPUs)
  • mycroft-mimic3-tts_<version>_arm64.deb
  • mycroft-mimic3-tts_<version>_armhf.deb
    • For Raspberry Pi 1/2/3/4 and Zero 2 with 32-bit Pi OS
Once downloaded, install the package with (note the ./):
sudo apt install ./mycroft-mimic3-tts_<VERSION>_<PLATFORM>.deb
Once installed, the following commands will be available in /usr/bin:
  • mimic3
  • mimic3-server
  • mimic3-download

Python Package

First, ensure that you're using the latest pip:
pip install --upgrade pip
Then, install the package:
pip install mycroft-mimic3-tts[all]
Removing [all] will install support for English only.
Additional language support can be selectively installed by replacing all with a two-character language code, such as de (German) or fr (French). See setup.py for an up-to-date list of language codes.
Once installed, the following commands will be available:
  • mimic3
  • mimic3-download
  • mimic3-server

From Source

Clone the repository:
git clone https://github.com/mycroftAI/mimic3.git
Run the install script:
cd mimic3/
./install.sh
A virtual environment will be created in mimic3/.venv and the mycroft-mimic3-tts Python module will be installed in editiable mode (pip install -e).
Once installed, the following commands will be available in .venv/bin:
  • mimic3
  • mimic3-server
  • mimic3-download

Usage

There are many ways to use Mimic 3, including:

Voice Keys

Voices in Mimic 3 are keyed by a name with specific parts. These parts include the voice's language, region, training dataset, quality level, and speaker.
Structure of a Mimic 3 voice key
The default voice is en_UK/apope_low
Voice models are automatically downloaded from Github and stored in ${HOME}/.local/share/mycroft/mimic3 (technically ${XDG_DATA_HOME}/mycroft/mimic3). You can also manually download them.

Command-Line Interface

Basic Synthesis

The mimic3 command can be used to synthesize audio on the command line:
mimic3 --voice <voice> "<text>" > output.wav
where <voice> is a voice key like en_UK/apope_low. <TEXT> may contain multiple sentences, which will be combined in the final output WAV file. These can also be split into separate WAV files.

SSML

A subset of Speech Synthesis Markup Language, or SSML, is available through the command line and web interface. SSML allows you to fine tune your output.
cat << EOF |
<speak>
<s>
Spoken before pause with default voice.
</s>
<break time="2s" />
<voice name="en_US/vctk_low#p236">
<s>
Spoken after pause in a different voice.
</s>
</voice>
</speak>
EOF
mimic3 --ssml --voice 'en_US/cmu-arctic#eey' > output.wav
SSML even lets you mix and match languages:
cat << EOF |
<speak>
<voice name="de_DE/thorsten_low">
<s>
Eine Sprache ist niemals genug.
</s>
</voice>
<voice name="nl/rdh_low">
<s>
Eén taal is nooit genoeg.
</s>
</voice>
<voice name="en_US/vctk_low">
<s>
One language is never enough.
</s>
</voice>
</speak>
EOF
mimic3 --ssml > output.wav
If your SSML contains <mark> tags, add --mark-file <file> to the command-line and use --interactive mode. As the marks are encountered, their names will be written on separate lines to the file:
mimic3 --ssml --interactive --mark-file - '<speak>Test 1. <mark name="here" /> Test 2.</speak>'
The following SSML tags are supported:
  • <speak> - wrap around SSML text
    • lang - set language for document
  • <s> - sentence (disables automatic sentence breaking)
    • lang - set language for sentence
  • <w> / <token> - word (disables automatic tokenization)
  • <voice name="..."> - set voice of inner text
  • <prosody attribute="value"> - change speaking attributes
    • Supported attribute names:
      • volume - speaking volume
        • number in [0, 100] - 0 is silent, 100 is loudest (default)
        • +X, -X, +X%, -X% - absolute/percent offset from current volume
        • one of "default", "silent", "x-loud", "loud", "medium", "soft", "x-soft"
      • rate - speaking rate
        • number - 1 is default rate, < 1 is slower, > 1 is faster
        • X% - 100% is default rate, 50% is half speed, 200% is twice as fast
        • one of "default", "x-fast", "fast", "medium", "slow", "x-slow"
  • <say-as interpret-as=""> - force interpretation of inner text
    • interpret-as one of "spell-out", "date", "number", "time", or "currency"
    • format - way to format text depending on interpret-as
      • number - one of "cardinal", "ordinal", "digits", "year"
      • date - string with "d" (cardinal day), "o" (ordinal day), "m" (month), or "y" (year)
  • <break time=""> - Pause for given amount of time
    • time - seconds ("123s") or milliseconds ("123ms")
  • <sub alias=""> - substitute alias for inner text
  • <phoneme ph=""> - supply phonemes for inner text
    • See phonemes.txt in voice directory for available phonemes
    • Phonemes may need to be separated by whitespace
SSML <say-as> support varies between voice types:
  • gruut
  • eSpeak-ng
  • Character-based voices do not currently support <say-as>
  • epitran based voices do not currently support <say-as>

Long Texts

If your text is very long, and you would like to listen to it as its being synthesized, use --interactive mode:
mimic3 --interactive < long.txt
Each input line will be synthesized and played (see --play-program). By default, 5 sentences will be kept in an output queue, only blocking synthesis when the queue is full. You can adjust this value with --result-queue-size.
If your long text is fixed-width with blank lines separating paragraphs like those from Project Gutenberg, use the --process-on-blank-line option so that sentences will not be broken at line boundaries. For example, you can listen to "Alice in Wonderland" like this:
curl --output - 'https://www.gutenberg.org/files/11/11-0.txt' | \
mimic3 --interactive --process-on-blank-line

Multiple WAV Output

With --output-dir set to a directory, Mimic 3 will output a separate WAV file for each sentence:
mimic3 'Test 1. Test 2.' --output-dir /path/to/wavs
By default, each WAV file will be named using the (slightly modified) text of the sentence. You can have WAV files named using a timestamp instead with --output-naming time. For full control of the output naming, the --csv command-line flag indicates that each sentence is of the form id|text where id will be the name of the WAV file.
cat << EOF |
s01|The birch canoe slid on the smooth planks.
s02|Glue the sheet to the dark blue background.
s03|It's easy to tell the depth of a well.
s04|These days a chicken leg is a rare dish.
s05|Rice is often served in round bowls.
s06|The juice of lemons makes fine punch.
s07|The box was thrown beside the parked truck.
s08|The hogs were fed chopped corn and garbage.
s09|Four hours of steady work faced us.
s10|Large size in stockings is hard to sell.
EOF
mimic3 --csv --output-dir /path/to/wavs
You can adjust the delimiter with --csv-delimiter <delimiter>.
Additionally, you can use the --csv-voice option to specify a different voice or speaker for each line:
cat << EOF |
s01|#awb|The birch canoe slid on the smooth planks.
s02|#rms|Glue the sheet to the dark blue background.
s03|#slt|It's easy to tell the depth of a well.
s04|#ksp|These days a chicken leg is a rare dish.
s05|#clb|Rice is often served in round bowls.
s06|#aew|The juice of lemons makes fine punch.
s07|#bdl|The box was thrown beside the parked truck.
s08|#lnh|The hogs were fed chopped corn and garbage.
s09|#jmk|Four hours of steady work faced us.
s10|en_UK/apope_low|Large size in stockings is hard to sell.
EOF
mimic3 --voice 'en_US/cmu-arctic_low' --csv-voice --output-dir /path/to/wavs
The second contain can contain a #<speaker> or an entirely different voice!

Interactive Mode

With --interactive, Mimic 3 will switch into interactive mode. After entering a sentence, it will be played with --play-program.
mimic3 --interactive
Reading text from stdin...
Hello world!<ENTER>
Use CTRL+D or CTRL+C to exit.

Noise and Length Settings

Synthesis has the following additional parameters:
  • --noise-scale and --noise-w
    • Determine the speaker volatility during synthesis
    • 0-1, default is 0.667 and 0.8 respectively
  • --length-scale - makes the voice speaker slower (> 1) or faster (< 1)
Individual voices have default settings for these parameters in their config.json files (under inference).

List Voices

mimic3 --voices

CUDA Acceleration

If you have a GPU with support for CUDA, you can accelerate synthesis with the --cuda flag. This requires you to install the onnxruntime-gpu Python package.
Using nvidia-docker is highly recommended. See the Dockerfile.gpu file in the parent repository for an example of how to build a compatible container.

Web Server

A small HTTP server is available for serving multiple clients. This is faster than the command-line interface since voice models only need to be loaded once.
screenshot of web interface

Running the Server

mimic3-server
This will start a web server at http://localhost:59125
To access the web server from a different device, run mimic3-server --host 0.0.0.0 (you can also change the port with --port).
Some other useful arguments to mimic3-server:
  • --preload-voice <VOICE_KEY> - loads a voice model at startup instead of on first use
  • --cache-dir <DIRECTORY> - caches WAV files in <DIRECTORY> (uses system temporary directory if no <DIRECTORY>)
  • --num-threads <THREADS> - use more than one thread of inference, increasing throughput for multiple clients
See mimic3-server --help for more options.

Endpoints

  • /api/tts
    • POST text or SSML and receive WAV audio back
    • Use ?voice= to select a different voice/speaker
    • Set Content-Type to application/ssml+xml (or use ?ssml=1) for SSML input
  • /api/voices
    • Returns a JSON list of available voices
An OpenAPI test page is also available at http://localhost:59125/openapi

CUDA Acceleration

If you have a GPU with support for CUDA, you can accelerate synthesis with the --cuda flag. This requires you to install the onnxruntime-gpu Python package.
Using nvidia-docker is highly recommended. See the Dockerfile.gpu for an example of how to build a compatible container.

Running the Client

Assuming you have started mimic3-server and can access http://localhost:59125, then run:
mimic3 --remote --voice 'en_UK/apope_low' 'My hovercraft is full of eels.' > hovercraft_eels.wav
If your server is somewhere besides localhost, use mimic3 --remote <URL> ...
See mimic3 --help for more options.

MaryTTS Compatibility

Use the Mimic 3 web server as a drop-in replacement for MaryTTS, for example with Home Assistant.
Make sure to use a Mimic 3 voice key like en_UK/apope_low instead of a MaryTTS voice name:
tts:
- platform: marytts
host: "localhost"
port: 59125
voice: "en_UK/apope_low"

Speech Dispatcher

WORK IN PROGRESS: This has not been tested on a broad range of systems. Some debugging may be required.
Mimic 3 can be used with the Orca screen reader for Linux via speech-dispatcher.
After installing Mimic 3, start the web server. Next, make sure you have speech-dispatcher installed:
sudo apt-get install speech-dispatcher
Create the file /etc/speech-dispatcher/modules/mimic3-generic.conf with the contents:
GenericExecuteSynth "printf %s \'$DATA\' | /path/to/mimic3 --remote --voice \'$VOICE\' --stdout | $PLAY_COMMAND"
AddVoice "en" "MALE1" "en_UK/apope_low"
You will need sudo access to do this. Make sure to change /path/to/mimic3 to wherever you installed Mimic 3. Note that the --remote option is used to connect to a local Mimic 3 web server (use --remote <URL> if your server is somewhere besides localhost).
To change the voice later, you only need to replace en_UK/apope_low.
Next, edit the existing file /etc/speech-dispatcher/speechd.conf and ensure the following settings are present:
DefaultVoiceType "MALE1"
DefaultModule mimic3-generic
DefaultLanguage "en"
AudioOutputMethod "libao"
Restart speech-dispatcher with:
sudo systemctl restart speech-dispatcher
and test it out with:
spd-say 'Hello from speech dispatcher.'

Systemd Service

To ensure that Mimic 3 runs at boot, create a systemd service at $HOME/.config/systemd/user/mimic3.service with the contents:
[Unit]
Description=Run Mimic 3 web server
Documentation=https://github.com/MycroftAI/mimic3
[Service]
ExecStart=/path/to/mimic3-server
[Install]
WantedBy=default.target
Make sure to change /path/to/mimic3-server to wherever you installed Mimic 3.
Refresh the systemd services:
systemctl --user daemon-reload
Now try starting the service:
systemctl --user start mimic3
If that's successful, ensure it starts at boot:
systemctl --user enable mimic3
Verify the web server is running by visiting http://localhost:59125

Downloading Voices

Mimic 3 automatically downloads voices when they're first used, but you can manually download them too with mimic3-download.
For example:
mimic3-download 'en_US/*'
will download all U.S. English voices to ${HOME}/.local/share/mycroft/mimic3/voices.
You can list the available voices with --voices:
mimic3 --voices | awk '{print $1}'
KEY
de_DE/m-ailabs_low
de_DE/thorsten_low
el_GR/rapunzelina_low
en_UK/apope_low
en_US/cmu-arctic_low
en_US/ljspeech_low
en_US/vctk_low
es_ES/carlfm_low
es_ES/m-ailabs_low
...
Voice models are stored locally in your home directory:
tree "${HOME}/.local/share/mycroft/mimic3/voices"
├── de_DE
│ ├── m-ailabs_low
│ │ ├── ALIASES
│ │ ├── config.json
│ │ ├── generator.onnx
│ │ ├── LICENSE
│ │ ├── phoneme_map.txt
│ │ ├── phonemes.txt
│ │ ├── README.md
│ │ ├── SOURCE
│ │ ├── speaker_map.csv
│ │ └── speakers.txt
...
Some voices even have multiple speakers. This one has over one hundred.
See mimic3-download --help for more options.

How It Works

Mimic 3 uses the VITS, a "Conditional Variational Autoencoder with Adversarial Learning for End-to-End Text-to-Speech". VITS is a combination of the GlowTTS duration predictor and the HiFi-GAN vocoder.
Our implementation is heavily based on Jaehyeon Kim's PyTorch model, with the addition of Onnx runtime export for speed.
mimic 3 architecture

Phoneme Ids

At a high level, Mimic 3 performs two important tasks:
  1. 1.
    Converting raw text to numeric input for the VITS TTS model, and
  2. 2.
    Using the model to transform numeric input into audio output
The second step is the same for every voice, but the first step (text to numbers) varies. There are currently four implementations of step 1, described below.

gruut Phoneme-based Voices

Voices that use gruut for phonemization.
gruut normalizes text and phonemizes words according to a lexicon, with a pre-trained grapheme-to-phoneme model used to guess unknown word pronunciations.

eSpeak Phoneme-based Voices

Voices that use eSpeak-ng for phonemization (via espeak-phonemizer).
eSpeak-ng normalizes and phonemizes text using internal rules and lexicons. It supports a large number of languages, and can handle many textual forms.

Character-based Voices

Voices whose "phonemes" are characters from an alphabet, typically with some punctuation.
For voices whose orthography (writing system) is close enough to its spoken form, character-based voices allow for skipping the phonemization step. However, these voices do not support text normalization, so numbers, dates, etc. must be written out.

Epitran-based Voices

Voices that use epitran for phonemization.
epitran uses rules to generate phonetic pronunciations from text. It does not support text normalization, however, so numbers, dates, etc. must be written out.

Components of a Voice Model

Voice models are stored in a directory with a specific layout:
  • <language>_<region> (e.g., en_UK)
    • <voice-name>_<quality> (e.g., apope_low)
      • ALIASES - alternative names for the voice, one per line (optional)
      • config.json - training/inference configuration (see code for details)
      • generator.onnx - exported inference model (see ids_to_audio method in voice.py)
      • LICENSE - text, name, or URL of voice model license
      • phoneme_map.txt - mapping from source phoneme to destination phoneme(s) (optional)
      • phonemes.txt - mapping from integer ids to phonemes (_ = padding, ^ = beginning of utterance, $ = end of utterance, # = word break)
      • README.md - description of the voice
      • SOURCE - URL(s) of the dataset(s) this voice was trained on
      • VERSION - version of the voice in the format "MAJOR.Minor.bugfix" (e.g. "1.0.2")

License

Mimic 3 is available under the AGPL v3 license

Feedback or questions?

Join us in Mycroft Chat or the Community Forums.
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On this page
Installation
Hardware Requirements
Software Requirements
TTS Plugin for Mycroft AI
Docker Image
Debian Package
Python Package
From Source
Usage
Voice Keys
Command-Line Interface
Web Server
Speech Dispatcher
Downloading Voices
How It Works
Phoneme Ids
gruut Phoneme-based Voices
eSpeak Phoneme-based Voices
Character-based Voices
Epitran-based Voices
Components of a Voice Model
License
Feedback or questions?