Spectrograms and speech processing

Last update : July 24, 2022

Spectrograms are visual representations of the spectrum of frequencies in a sound or other signal as they vary with time (or with some other variable). Spectrograms can be used to identify spoken words phonetically. The instrument that generates a spectrogram is called a spectrograph.

Spectrograms are approximated as a filterbank that results from a series of bandpass filters or calculated from the time signal using the Fast Fourier Transform (FFT).

FFT is an algorithm to compute the Discrete Fourier Transform (DFT) and its inverse. A significative parameter of the DFT is the choice of the Window Function. In signal processing, a window function is a mathematical function that is zero-valued outside of some chosen interval. The following window functions are common for spectrograms :

I recorded a sound example.wav file with my name spoken three times, to use as test file for different spectrogram software programs.

Real-Time Spectrogram Software

There are some great software programs to perform a spectrogram for speech analysis in realtime or with recorded sound files :

  • Javascript Spectrogram
  • Wavesurfer
  • Spectrogram16
  • Audacity
  • RTS
  • iSound

Javascript Spectrogram

Jan Schnupp, sensory neuroscientist, former Professor at the Department of Physiology, Anatomy and Genetics within the Division of Medical Sciences at the University of Oxford, developed an outstanding javascript program to calculate and display a real-time spectrogram in a webpage, from the input to the computer’s microphone. It requires a browser which supports HTML5 and web audio and it requires also WebRTC, which is supported in recent versions of Chrome, Firefox and Opera browsers. WebRTC is a free, open project that enables web browsers with Real-Time Communications (RTC) capabilities via simple JavaScript APIs.

Javascript spectrogram with 3x voice sound "Marco Barnig"

Javascript realtime spectrogram with 3x voice input “Marco Barnig” by microphone

Jan Schnupp  is currently Professor of Neuroscience at the City University of Hong Kong. He is also the author of the website howyourbrainworks.net offering free, accessible introductory online lecture courses to neuroscience.


WaveSurfer is an open source multiplatform tool for sound visualization and manipulation. Typical applications are speech/sound analysis and sound annotation/transcription. WaveSurfer may be extended by plug-ins as well as embedded in other applications. A comprehensive user manual and numerous tutorials for Wavesurfer are available on the net.

WaveSurfer was developed at the Centre for Speech Technology (CCT) at the KTH Royal Institute of Technology in Sweden. The latest stable Windows release (1.8.8p6, May 7, 2020) and the source code of WaveSurfer can be downloaded from Sourceforge. The authors of Wavesurfer are Jonas Beskow and Kåre Sjölander.

wavesurfer auto

Wavesurfer auto-calculated, auto-sized spectrogram

By right-clicking in the Wafesurfer pane, a pop-up window opens with menus to add more panes, to customize the configuration and to change the parameters for analysis. In the following rendering, the panes Waveform, Pitch Contour, Formant Plot and Transcription have been added to the spectrogram pane and to the Time Axis pane. The spectrogram frequency range was cut at 5 KHz.

Wafesurfer customized

Wafesurfer customized

Two other panes can be selected: Power Plot and Data Plot. Additional specific panes can be created with plugins.

Wavesurfer uses the Snack Sound Toolkit created by Kåre Sjölander. There exist other software programs with the name Wavesurfer, for example wavesurfer.js, a customizable waveform audio visualization tool, built on top of Web Audio API and HTML5 Canvas by katspaugh.


Spectrogram16 is a calibrated, dual channel audio spectrum analyzer for Windows that can provide either a scrolling time-frequency display or a spectrum analyzer scope display in real time for any sound source connected to the sound card. A detailed user guide (51 pages) is joined to the program.

Spectrogram16 customized

Spectrogram16 customized

The tool was created by Richard Horne, the founder of Visualization Software LLC. The company closed  a few years ago. The WayBackMachine shows that Richard Horne announced in 2008 that version 16 of Spectrogram is now freeware (see also local copy). The software is still available from most  free software download websites. Richard Horne, MS, who retired as a Civilian Electrical Engineer for the Navy, was member of the Management Team of Vocal Innovations.

The Spectrogram program was (and is still) appreciated by amateur radio operators for aligning ham receivers.


RTGRAM is a free Windows program for displaying a real-time scrolling spectrographic display of an audio signal. With RTGRAM you can monitor the spectro-temporal characteristics of sounds being played into the computer’s microphone or line input ports. RTGRAM is optimised for speech signals and has options for different sampling rates, analysis bandwidths (wideband = 300 Hz, narrowband = 45 Hz), temporal resolution (time per pixel = 1 – 10 ms), dynamic range (30 – 70 dB) and colour maps.


RTGRAM realtime spectrogram with 3x voice input “Marco Barnig” by microphone

The current version of RTGRAM is 1.3, released in April 2010. It is part of the Speech Filing System (SFS) tools for speech research.

RTGRAM is free, but not public domain software, its intellectual property is owned by Mark Huckvale, University College London.


Audacity is a free, open source, cross-platform software for recording and editing sounds. Audacity was started in May 2000 by Dominic Mazzoni and Roger Dannenberg at Carnegie Mellon University. The current version is 3.0.3, released on July 26, 2021.


Audacity auto-calculated, auto-sized spectrogram

A huge documentation about Audacity with manuals, tutorials, tips, wikis, FAQ’s is available in several languages.

RTS tm

RTS (Real-Time Spectrogram) is a product of Engineering Design, founded in 1980 to address problems in instrumentation and measurement, physical acoustics, and digital signal analysis. Since 1984, Engineering Design has been the developer of the SIGNAL family of sound analysis software. RTS is highly integrated with SIGNAL.


STRAIGHT (Speech Transformation and Representation by Adaptive Interpolation of weiGHTed spectrogram) was originally designed to investigate human speech perception in terms of auditorily meaningful parametric domains. STRAIGHT is a tool for manipulating voice quality, timbre, pitch, speed and other attributes flexibly. The tool was invented by Hideki Kawahara when he was in the Advanced Telecommunications Research Institute International (ATR) in Japan. Hideki Kawahara is now Emeritus Professor from the Wakayama University, Japan.


Irman Abdić created an audio tool (iSound) for displaying spectrograms in real time using Sphinx-4 as part of his thesis at the Faculty of Mathematics, Natural Sciences and Information Technologies (FAMNIT) from Koper, Slovenia.

No Real-Time Spectrogram Software

Other great software programs to create no-realtime spectrograms of recorded voice samples are :

  • Praat
  • SoX
  • SFS / WASP
  • Sonogram Visible Speech


Praat (= talk in dutch) is a free scientific computer software package for the analysis of speech in phonetics. It was designed, and continues to be developed, by Paul Boersma and David Weenink of the Institute of Phonetics Sciences at the University of Amsterdam. Praat runs on a wide range of operating systems. The program also supports speech synthesis, including articulatory synthesis.
Praat displays two windows : Praat Objects and Praat Picture.

Praat Objects Window

Praat Objects Window

Praat Picture Window

Praat Picture Window

The spectrogram can also be rendered in a customized window.


Praat customized window

The current version 6.1.51 of Praat was released on August 25, 2021. The source code for this release is available at Github. A huge documentation with FAQ’s, tutorials, publications, user guides is available for Praat. The plugins are located in the directory C:/Users/name/Praat/.

An outstanding plugin for Praat is EasyAlign. It is a user-friendly automatic phonetic alignment tool for continuous speech. It is possible to align speech from an orthographic or phonetic transcription. It requires a few minor manual steps and the result is a multi-level annotation within a TextGrid composed of phonetic, syllabic, lexical and utterance tiers. EasyAlign was developed by Jean-Philippe Goldman at the Department of Linguistics, University of Geneva.


SoX (Sound EXchange) is a free cross-platform command line utility that can convert various formats of computer audio files in to other formats. It can also apply various effects to these sound files and play and record audio files on most platforms. SoX is called the Swiss Army knife of sound processing programs.

SoX is written in standard C and was created in July 1991 by Lance Norskog. In May 1996, Chris Bagwell started to maintain and release updated versions of SoX. Throughout its history, SoX has had many contributing authors. Today Chris Bagwell is still the main developer.

The current Windows distribution is 14.4.2 released  in February 22, 2015. The source code is available at Sourceforge.

SoX provides a very powerful spectrogram effect. The spectrogram is rendered in a png image-file and shows time in the x-axis, frequency in the y-axis and audio signal amplitude in the z-axis. The z-axis values are represented by the colour of the pixels in the x-y plane. The command

sox example.wav -n spectrogram

creates the following auto-calculated, auto-sized spectrogram :

SoX auto

SoX auto-calculated, auto-sized spectrogram

The main options to customize a spectrogram created with SoX are :

-x num : change the width of the spectrogram from its default value of 800px
-Y num : sets the total height of the spectrogram; the default value is 550px
-z num : sets the dynamic range from 20 to 180 dB; the default value is 120 dB
-q num : sets the z-axis quantisation (number of different colours)
-w name : select the window function; the default function is Hann
-l : creates a printer-friendly spectrogram with a light background
-a : suppress the display of the axis lines
-t text : set an image title
-c text : set an image comment (below and to the left of the image)
-o text : set the name of the output file; the default name is spectrogram.png
rate num k : analyse a small portion of the frequency domain (up to 1/2 num kHz)

A customized rendering follows :


Customized SoX spectrogram

The customized SoX spectrogram was created with the following command :

sox example.wav -n rate 10k spectrogram -x 480 -y 240 -q 4 -c "www.web3.lu" 
-t "SoX Spectrogram of the triple speech sound Marco Barnig"


WASP is a free Windows program for the recording, display and analysis of speech. With WASP you can record and replay speech signals, save them and reload them from disk, edit annotations, and display spectrograms and a fundamental frequency track. WASP is a simple application that is complete in itself, but which is also designed to be compatible with the Speech Filing System (SFS) tools for speech research. The current version 1.80 was released in June 2020.
The following figure shows a customized WASP window with a  speech waveform pane, a wideband spectrogram, a pitch track and annotations.

WASP customized spectrogram

WASP customized spectrogram with pitch and annotation tracks

WASP is free, but not public domain software, its intellectual property is owned by Mark Huckvale, University College London.

Sonogram Visible Speech

Sonogram Visible Speech is a very advanced program for sound, music and speech analysis. It provides multiple tools to perform various transformations and spectral studies on audio signals and to display the results in numerous panels : perspectogram, pitch, wavelet, cepstrum, 3D plots, auto-correlation charts etc.

In short terms, Sonogram is a  powerful and complex audio spectrum analyzer with a comprehensive GUI layout.

Sonogram Visible Speech Main Window

Sonogram is programmed in Java and needs Java Runtime in version 16 at least. It runs in Windows, MacOS and Unix/Linux. The current version 5 has been released in August 18, 2021. The source code is available at Github. The next figure shows the start of the program in a Linux terminal.

Program Start with Sonogram.sh

The following files show the help-, settings- and info-panels:

Sonogram Online Help


Sonogram Settings


Sonogram Detailed Info

Sonogram includes a 3D-chart to present processed sound signals in three dimensions and a convenient audio recorder.

3D Perspectogram


Sonogram Audio Recorder

Sonogram Visible Speech was programed from 2000 to 2021 by Christoph Lauer. When he started the project he worked at the DFKI (Deutsches Forschungsinstitut für künstliche Intelligenz) in Saarbrücken. In December 2007 he joined the Saarland University as a scientific assistant, two years later the IDTM (Fraunhofer Institute for Digital Media Technology) as an Audio DSP Researcher. Since 2014 Christoph Lauer  works as a Machine Learning Researcher for the BMW Group.

Specific Spectrogram Software

Spectrograms can also be used for teaching, artistic or other curious purposes :

  • FaroSon
  • SpectroTyper
  • ImageSpectrogram


FaroSon (The Auditory Lighthouse), is a Windows program for the real-time conversion of sound into a coloured pattern representing loudness, pitch and timbre. The loudness of the sound is reflected in the brightness and saturation of the colours. The timbre of the sound is reflected in the colours themselves: sounds with predominantly bass character have a red colour, while sounds with a predominantly treble character have a blue colour. The pitch of the sound is reflected in the horizontal banding patterns: when the pitch of the sound is low, then the bands are large and far apart, and when it is high, the bands are narrow and close together. If the pitch of the sound is falling you see the bands diverge; when it is rising, you see the bands converge.



FaroSon is free, but not public domain software, its intellectual property is owned by Mark Huckvale, University College London.


AudioCheck offers the Internet’s largest collection of online sound tests, test tones, and tone generators. Audiocheck provides a unique online tool called SpectroTyper to insert plain text into a .wav sound file. The downloaded file plays as cool-sounding computer-like tones and is secretly readable from a spectrogram view (linear frequency scale best). It can be used for fun, to hide easter eggs in a music production or to tag copyrighted audio material with own identifiers or source informations.

Here is the barnig_txt.wav sound file with my integrated name as an example, the result is shown below in the SoX spectrogram, created with the command :

sox barnig_txt.wav -n rate 10k spectrogram -x 480 -y 120

SoX Spectrogram of a sound with inserted text, synthesized with SpectroTyper

SpectroTyper and other audio tools and tone generators have been created by Stéphane Pigeon, a research engineer & sound designer from Belgium. He received the degree of electrical engineering from the Université Catholique de Louvain (UCL) in June 1994, with a specialization in signal processing. He finalized a PhD thesis in applied science in 1999. Then, Stéphane Pigeon joined the Royal Military Academy as a part-time researcher. In parallel, he worked as a consultant, exclusively for Roland Corporation in the area of the musical instrument market. He designed various audio-related websites, like AudioCeck.net started in 2007. He also released some iOS apps. His most succesful project is myNoise.net, started in 2013, which offers a unique collection of online noise generators.


Richard David James, best known by his stage name Aphex Twin, is an British electronic musician and composer. In 1999, he released Windowlicker as a single on Warp Records. In this record he synthesized his face as a sound, only viewable in a spectrogram.

Gavin Black (alias plurSKI) created a perl script to do the same : take a digital picture and convert it into a wave file. Creating a spectrogram of that file then reproduces the original picture.

Here is the barnig_portrait.wav sound file with my integrated portrait as an example, the result is shown below in the SoX spectrogram, created with the command :

sox barnig_portrait.wav -n spectrogram -x 480 -y 480

SoX Spectrogram of a sound with inserted picture, synthesized with imageSpectrogram

On July 24, 2022, Scott Duplichan published an Audio SpectrumViewer for Windows on Sourceforge. During the development he used the wav-sample with my embedded portrait to test his realtime spectrum viewer. Scott found a converter to create a better image with a smaller wav-file.

The spectrum viewer app contains a demo folder with an audioFileImage subfolder where you can start batch-files to compare the original with the improved spectrum. The result with the new converter is shown in the following screen-shot:


A list with links to websites providing additional informations about spectrograms is presented below :

Mary TTS (Text To Speech)

Last update : January 5, 2017

MaryTTS is an open-source, multilingual Text-to-Speech Synthesis platform written in Java. It was originally developed as a collaborative project of DFKI’s Language Technology Lab and the Institute of Phonetics at Saarland University. It is now maintained by the Multimodal Speech Processing Group in the Cluster of Excellence MMCI and DFKI (Deutsches Forschungszentrum für Künstliche Intelligenz GmbH).

Mary stands for Modular Architecture for Research in sYynthesis. The earliest version of MaryTTS was developed around 2000 by Marc Schröder. The current stable version is 5.2, released on September 15, 2016.

I installed Mary TTS on my Windows, Linux and Mac computers. On the Mac (OSX 10.10 Yosemite), version 5.1.2 of Mary TTS was placed on the desktop in the folders marytts-5.1.2 and marytts-builder-5.1.2. The Mary TTS Server is started first by opening a terminal window in the folder marytts-5.1 with the following command :

marytss-5.1.2 mbarnig$ bin/marytts-server.sh

To start the Mary TTS client with the related GUI, a second terminal window is opened in the same folder  with the command :

marytss-5.1.2 mbarnig$ bin/marytts-client.sh

On Windows , the related scripts are marytts-server.bat and marytts-client.bat.

As the development version 5.2 of Mary TTS supports more languages and comes with toolkits for quickly adding support for new languages and for building unit selection and HMM-based synthesis voices, I downloaded a snapshot-zip-file from Github with the most recent source code. After unzipping, the source code was placed in the folder marytts-master on the desktop.

To compile Mary TTS from source on the Mac, the latest JAVA development version (jdk-8u31-macosx-x64.dmg) and Apache Maven (apache-maven-3.2.5-bin.tar.gz), a software project management and comprehension tool, are required.

On Mac, Java is installed in


and Maven is installed in


It is important to set the environment variables $JAVA_HOME, $M2_HOME and the $PATH to the correct values (export in /Users/mbarnig/.bash-profile).

The succesful installation of Java and Maven can be verified with the commands :

mbarnig$ java -version
mbarnig$ mvn --version


Mary TTS : Maven and Java versions

This looks good!

In the next step I compiled the Mary TTS source code by running the command

marytts-master mbarnig$ mvn install

in the top-level marytts-master folder. This build the system, run unit and integration tests, packaged the code and installed it in the following folders :


The build took 2:55 minutes and was succesful, without errors or warnings.


Results of building MARYTTS 5.2 SNAPSHOT

The following modules have been compiled :

  • MaryTTS
  • marytts-common
  • marytts-signalproc
  • marytts-runtime
  • marytts-lang-de, en, te, tr, ru, it, fr, sv, lx (lx is a pseudo locale for a test language)
  • marytts-languages
  • marytts-client
  • marytts-builder
  • marytts-redstart
  • marytts-transcription
  • marytts-assembly with the sub-modules assembly-builder and assembly-runtime
  • voice_cmu_slt_hsmm

After checking the whole file structure, I started the Mary TTS 5.2 server


Mary TTS snapshot 5.2 Server

and the Mary TTS 5.2 client


Mary TTS Snapshot 5.2 client

did some trials with text to audio conversion in the GUI window


Mary TTS Client GUI

launched the Mary TTS 5.2 component installer

Mary TTS Component Installer

Mary TTS Component Installer

and finally installed some french, german and english available voices.


Mary TTS Voice Installer GUI

In the next step I will try to create my own voices and develop a voice for the luxembourgish language.

In January 2017, I updated my systems with the stable MaryTTS version 5.2 which supports the luxembourgish language.

eSpeak Formant Synthesizer

Last update : November 2, 2014


eSpeak is a compact multi-platform multi-language open source speech synthesizer using a formant synthesis method.

eSpeak is derived from the “Speak” speech synthesizer for British English for Acorn Risc OS computers, developed by Jonathan Duddington in 1995. He is still the author of the current eSpeak version 1.48.12 released on November 1, 2014. The sources are available on Sourceforge.

eSpeak provides two methods of formant synthesis : the original eSpeak synthesizer and a Klatt synthesizer. It can also be used as a front end for MBROLA diphone voices. eSpeak can be used as a command-line program or as a shared library. On Windows, a SAPI5 version is also installed. eSpeak supports SSML (Speech Synthesis Marking Language) and uses an ASCII representation of phoneme names which is loosely based on the Kirshenbaum system.

In formant synthesis, voiced speech (vowels and sonorant consonants) is created by using formants. Unvoiced consonants are created by using pre-recorded sounds. Voiced consonants are created as a mixture of a formant-based voiced sound in combination with a pre-recorded unvoiced sound. The eSpeakEditor allows to generate formant files for individual vowels and voiced consonants, based on a sequence of keyframes which define how the formant peaks (peaks in the frequency spectrum) vary during the sound. A sequence of formant frames can be created with a modified version of Praat, a free scientific computer software package for the analysis of speech in phonetics. The Praat formant frames, saved in a spectrum.dat file, can be converted to formant keyframes with eSpeakEdit.

To use eSpeak on the command line, type

espeak "Hello world"

There are plenty of command line options available, for instance to load from file, to adjust the volume, the pitch, the speed or the gaps between words, to select a voice or a language, etc.

To use the MBROLA voices in the Windows SAPI5 GUI or at the command line, they have to be installed during the setup of the program. It’s possible to rerun the setup to add additional voices. To list the available voices type

espeak --voices

eSpeak uses a master phoneme file containing the utility phonemes, the consonants and a schwa. The file is named phonemes (without extension) and located in the espeak/phsource program folder. The vowels are defined in the language specific phoneme files in text format. These files can also redefine consonants if you wish. The language specific phoneme text-files are located in the same espeak/phsource folder and must be referenced in the phonemes master file (see example for luxembourgish).

phonemetable lb base
include ph_luxembourgish

In addition to the specific phoneme file ph_luxembourgish (without extension), the following files are requested to add a new language, e.g. luxembourgish :

lb file (without extension) in the folder espeak/espeak-data/voices : a text file which in its simplest form contains only 2 lines :

name luxembourgish
language lb

lb_rules file (without extension) in the folder espeak/dictsource : a text file which contains the spelling-to-phoneme translation rules.

lb_list file (without extension) in the folder espeak/dictsource : a text file which contains pronunciations for special words (numbers, symbols, names, …).

The eSpeakEditor (espeakedit.exe) allows to compile the lb_ files into an lb_dict file (without extension) in the folder espeak/espeak-data and to add the new phonemes into the files phontab, phonindex and phondata in the same folder. These compiled files are used by eSpeak for the speech synthesis. The file phondata-manifest lists the type of data that has been compiled into the phondata file. The files dict_log and dict_phonemes provide informations about the phonemes used in the lb_rules and lb_dict files.

eSpeak applies tunes to model intonations depending on punctuation (questions, statements, attitudes, interaction). The tunes (s.. = full-stop, c.. = comma, q.. = question, e.. = exclamation) used for a language can be specified by using a tunes statement in the voice file.

tunes s1  c1  q1a  e1

The named tunes are defined in the text file espeak/phsource/intonation (without extension) and must be compiled for use by eSpeak with the espeakedit.exe program (menu : Compile intonation data).


Three years ago, Matthew Temple ported the eSpeak program from C++ to JavaScript using Emscripten : speak.js. Based on this Javascript project, Norbert Landsteiner from Austria created the meSpeak.js text-to-speech web library. The latest version is 1.9.6 released in February 2014.

meSpeak.js is supported by most browsers. It introduces loadable voice modules. The typical usage of the meSpeak.js library is shown below :

<!DOCTYPE html>
<html lang="en">
 <title>Bonjour le monde</title>
 <script type="text/javascript" src="mespeak.js"></script>
 <script type="text/javascript">
 function speakIt() {
 meSpeak.speak("Bonjour le monde");
<h1>Try meSpeak.js</h1>
<button onclick="speakIt();">Speak It</button>

Click here to test this example.

The mespeak_config.json file contains the data of the phontab, phonindex, phondata and intonations files and the default configuration values (amplitude, pitch, …). This data is encoded as base64 octed stream. The voice.json file includes the id of the voice, the dictionary used and the corresponding binary data (base64 encoded) of these two files. There are various desktop or online Base64 Decoders and Encoders available on the net to create the required .json files (base64decode.org, motobit.com, activexdev.com, …).

meSpeak cam mix multiple parts (diiferent languages or voices) in a single utterance.meSpeak supports the Web Audio API (AudioContext) with internal wav files, Flash is used as a fallback.


A list with links to websites providing additional informations about eSpeak and meSpeak follows :

Supertoy Teddy and Huggable

Supertoy Teddy

Supertoy Teddy

Supertoy Teddy is the world’s first talking teddy with a mind of its own and the ability to hold real conversations with those who speak to it. It has been developed by Ashley Conlan (CEO of Supertoy Robotics) and Kartsen Fluegge (CEO of Pannous GmbH), the creators of the successful app Jeannie, the Siri style chatbot that has been downloaded over 3 million times on mobile devices.

Supertoy Teddy uses artificial intelligence (AI). A smartphone acts as its brawn and the internet server as its brain. Supertoy Teddy’s robotic mouth moves in synchronization to what it says and inbuilt speakers enhance the volume of its voice. Role play will be added to the Supertoy Teddy and several costumes and dresses will be sold at the online shop.

The robot’s hardware is simple: just an audio in/out interface and a motor for mouth animation. Supertoy Teddy connects via standard audio plug to an iOS or Android device. Asley Conlan suggests putting the phone inside the Supertoy for realism. The magic is in the software, which has evolved from the popular Jeannie chatbot app.

[jwplayer player=”1″ mediaid=”12984″]

The creators of Supertoy Teddy have started a Kickstarter campaign for crowdfunding during the funding period July 24, 2013 – August 23, 2013. I am one of the bakers of the project.

Huggable (MIT)

Huggable (MIT)

Huggable is a similar type of robotic companion that has being developed at the MIT Media Lab (Personal Robots Group) for healthcare, education, and social communication applications a few years ago. The early technical development of the Huggable was supported in part by a Microsoft iCampus grant in 2006.

Google text to speech (TTS) with processing

Referring to the post about Google STT, this post is related to Google speech synthesis with processing. Amnon Owed presented in November 2011 processing code snippets to make use of Google’s text-to-speech webservice. The idea was born in the processing forum.

The sketch makes use of the Minim library that comes with Processing. Minim is an audio library that uses the JavaSound API, a bit of Tritonus, and Javazoom’s MP3SPI to provide an easy to use audio library for people developing in the Processing environment. The author of Minim is Damien Di Fede (ddf), a creative coder and composer interested in interactive audio art and music games. In November 2009, Damien was joined by Anderson Mills who proposed and co-developed the UGen Framework for the library.

I use the Minim 2.1.0 beta version with this new UGen Framework. I installed the Minim library in the libraries folder in my sketchbook and deleted the integrated 2.0.2 version in the processing (2.0b8) folder modes/java/libraries.

Today I run succesful trials with the english, french and german Google TTS engine. I am impressed by the results.

Voice driven web applications

Last update : July 17, 2013

The new JavaScript Web Speech API specified by W3C makes it easy to add speech recognition to a web page and to create voice driven web applications. It enables developers to use scripting to generate text-to-speech output and to use speech recognition as an input for forms, continuous dictation and control. The JavaScript API allows web pages to control activation and timing and to handle results and alternatives.

The Web Speech specification was published by the Speech API Community Group, chaired by Glen Shires, software engineer at Google. The specification is not a W3C Standard nor is it on the W3C Standards Track.

A demo working in the Chrome browser 25 and later is available at the HTML5 rocks website.

There are two processes : Text-to-Speech (speech synthesis : TTS) and Speech-to-Text (speech recognition : ASR). There are at least three different approaches to synthesize text :

  • integrated :  a TTS module is built into the OS, or a separately installed TTS engine can plug-in to the OS’s TTS module.
  • packaged : instead of requiring a separate install, a synthesizer and voices can be packaged and shipped with the application.
  • in the cloud : a web-service is used to synthesize text. The advantage of this is a more predictable and consistent voice quality, independent from the hardware and operation system used on the mobile client.

Concerning ASR, Wolf Paulus, an internationally experienced technologist and innovator, compared the performance (speed and accuracy) of the speech recognition systems developed by Google, Nuance, iSpeech and AT&T.

A HTML Speech XG Speech API Proposal, introduced by Microsoft to the  HTML Speech Incubator Group, is available as unofficial draft at the W3C website.

A list of speech recognition software is available at Wikipedia. The main hosted speech applications are presented below :


iSpeech provides speech solutions for individuals and business, in different fields as mobiles, connected homes, automotive, publishing (audio books), e-learning and more. The solutions include Text-to-speech (TTS) and speech recognition (ASR).

iSpeech offers API’s and SDK for developers for different devices and programming languages (iPhone, Android, Blackberry, PHP, JAVA, Python, .NET, Flash, Ruby, Perl) and comprehensive documentations, integration guides, web samples and FAQ’s. iSpeech povides development keys to use the three servers :

  • Mobile Development
  • Mobile Production
  • Web/General/Desktop/Other Production

The applications must be configured to use the correct servers.To make the web/general key work, you need to buy credits. The low usage price is $0.02 per word (TTS) or per transaction (ASR).

An free iSpeech app for iOS devices (version 1.3.5 updated May 13, 2013) to convert text to speech with the best sounding voices is available at the iTune store. This app is powered by the iSpeech.org Text to Speech (TTS) software as a service (SaaS) API. Other apps for iOS and Android devices are listed at the iSpeech website. A Text-to-Speech demo is also available.


Nuance Communications is a multinational computer software technology corporation, headquartered in Burlington, Massachusetts, that provides speech and imaging applications.

In August 2012, Nuance announced Nina, a collection of personal assistant technologies that will bring Siri-like functionality to customer service mobile apps.

Nuance provides the Dragon Mobile SDK to developers that joined the NDEV Dragon Mobile developer program. This creates a unique opportunity in the mobile developer ecosystem to power any application with Nuance’s proven, best-in-class Dragon Naturally Speaking voice recognition technology.

In joining NDEV Mobile, developers have free access to wrappers and widgets for simple application customization, all through a self-service website. Developers also have access to an on-line community forum for support, a variety of code samples and full documentation. Once an NDEV Mobile developer has integrated the SDK into their application, Nuance provides 90 days of free access to the cloud-based speech services to validate the power of speech recognition on their application. To put an application in production, a licence fee of 3.000 $ has to be prepaid.The low usage price is 0,009 $ per transaction.

The following platforms are supported :

  • Apple  iOS
  • Android
  • Windows Phone
  • HTTP web services interface

A mobile assistant & voice app for iOS and Android is available in the iTunes at GooglePlay stores.

AT&T Watson Speech engine

AT&T offers a free speech development program to access the tools needed to build, test, onboard and certify applications across a range of devices, OSes and platforms.

There are three classes of functionality in the AT&T speech API family :

  • Speech to Text : 9 contexts are optimized to return the text of what the end users say. The text can be returned in multiple formats, including, JSON and XML.
  • Text to Speech : Male and female ‘characters’ are available for both English and Spanish.
  • Speech to Text Custom :  the speech service is customized by sending a list of words or phrases commonly spoken by the end users to improve recognition of those unique words. The Grammar List supports 19 languages, the Generic with Hints supports English and Spanish.

The Call Management (Beta) API that is powered by Tropo™ exposes SMS and Voice Calling RESTful APIs, which enable app developers to create voice-enabled apps that send or receive calls, provide Interactive Voice Response (IVR) logic, Automatic Speech Recognition (ASR), Voice to Text (VTT), Text (SMS) integration, and more. SDK’s are available for HTML5 (Sencha Touch), Android, iOS and Microsoft. Tools are provided for key platforms, including Android, Brew MP, HTML5, RIM BlackBerry and Windows Phone.

The Speech API provides two methods for transcribing audio into text and one method for rendering text into audio. An AT&T Natural Voices Text-to-Speech Demo is availbale at the AT&T research website.

API access to the AT&T sandbox and production environments costs 99$ a year. The sandbox and production environments allow you to develop, test, and deploy applications using AT&T APIs, including 1 million points (one transaction = one point) each month to spend on any APIs they like. A US based credit card is required to charge 20$ for each additional group of 2,000 points exceeding one million. See the AT&T pricelist.

AT&T Application Resource Optimizer (ARO) is a free diagnostic tool for analyzing the performance of your mobile applications. It can help your app run faster and smarter by providing recommendations to help optimize your mobile application’s performance, speed, network impact and battery utilization.

Speech API FAQ’s as well as code samples, documents, tutorials, guides, SDK’s, tools, blogs, forums and more are available at the AT&T speech development website.

Google Speech API

The Google Speech API can be accessed safely through a Chrome browser using x-webkit-speech. Some people have reverse engineered the Google speech API for other uses on the web. The interface is free, but it is not an official public API.

On February 23, 2013, Google announced at the Chrome Blog that the new stable Chrome release includes support for the Web Speech API, which developers can use to integrate speech recognition capabilities into their web apps in more than 30 languages. A web speech API demo is available at the Google website. In the Peanut Gallery, you can add intertitles to old black-and-white movies simply by talking to Chrome.

The following list provides links to more informations about the Google speech API’s :

More speech applications from other suppliers are listed hereafter :

The Eclipse Voice Tools Project (VTP) allows you to build and run speech recognition application using industry standards such as VoiceXML and Speech Recognition Grammar Specification (SRGS).

MMDAgent toolkit

Last update : August 9, 2013



MMDAgent is a toolkit for building voice interaction systems. The toolkit is released for contributing to the popularization of speech technology. Users can design users own dialog scenario, 3D agents, and voices. This software is released under the New and Simplified BSD license. Version 1.3.1 was released on December 25, 2012, and is available at the SourceForge website. The toolkit was created by the Department of Computer Science at the Nagoya Institute of Technology, Japan. The current members of the project team are Keiichi Tokuda, Akinobu Lee and Keiichiro Oura.

MMDAgent  employs MikuMikuDance (MDD) as a foundation for its 3D rendering system, as well as allowing users to maintain a lively conversation with their 3D companion. Hatsune Miku is one of the many models that can be used to hold a conversation with.

MMDAgent speech recognition

The speech recognition module of MMDAgent is based on Julius, the open-source large-vocabulary continuous speech recognition engine. New words to be recognized to MMDAgent can be added by making a user dictionary.

An MMDAgent WordPress Blog with news about the project was launched in August 2012.