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MBROLA is a speech synthesizer based on the concatenation of diphones
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Welcome to MBROLA project

Table of contents

A brief description of MBROLA

MBROLA is a speech synthesizer based on the concatenation of diphones. It takes a list of phonemes as input, together with prosodic information (duration of phonemes and a piecewise linear description of pitch), and produces speech samples on 16 bits (linear), at the sampling frequency of the diphone database.

Please look at MBROLA-voices project homepage to get the voices.

It is therefore NOT a Text-To-Speech (TTS) synthesizer, since it does not accept raw text as input. In order to obtain a full TTS system, you need to use this synthesizer in combination with a text processing system that produces phonetic and prosodic commands.

The synthesizer uses a synthesis method known itself as MBROLA.

See more at development history.


You need C compiler and libraries to compile the project. On Debian-based Linux you need to install following packages:

sudo apt-get install make gcc

To compile your own binary, execute command:


To clean project, execute command:

make clean

Look for makefile details, if compilation is not successful.

More documentation for developers is located in Documentation folder of the project.


First try:


from Bin folder of the project to see the terms and conditions on the use of this software.

Then try:

mbrola -h

to get some help on how to use the software, e.g.:

 USAGE: mbrola [COMMAND LINE OPTIONS] database pho_file+ output_file

A - instead of pho_file or output_file means stdin or stdout
Extension of output_file ( raw, au, wav, aiff ) tells the wanted audio format

Options can be any of the following:
-i = display the database information if any
-e = IGNORE fatal errors on unkown diphone
-c CC = set COMMENT char (escape sequence in pho files)
-F FC = set FLUSH command name
-v VR = VOLUME ratio, float ratio applied to ouput samples
-f FR = FREQ ratio, float ratio applied to pitch points
-t TR = TIME ratio, float ratio applied to phone durations
-l VF = VOICE freq, target freq for voice quality
-R RL = Phoneme RENAME list of the form a A b B ...
-C CL = Phoneme CLONE list of the form a A b B ...

-I IF = Initialization file containing one command per line
 and IGNORE are available
-W = store the datbase in ROM format
-w = the database in a ROM dump
-d = Show list of diphones in the database

Now in order to go further, you need to get a version of an MBROLA language/voice database from the MBROLA project homepage. Let us assume you have copied the FR1 database and referred to the accompanying fr1.txt file for its installation.

Then try e.g.: mbrola fr1/fr1 fr1/TEST/bonjour.pho bonjour.wav

it uses the format:

mbrola diphone_database command_file1 command_file2 ... output_file

and creates a sound file for the word 'bonjour'.

Basically the output file is composed of signed integer numbers on 16 bits, corresponding to samples at the sampling frequency of the MBROLA voice/language database (16 kHz for the diphone database supplied by the author of MBROLA : Fr1). MBROLA can produce different audio file formats: .au, .wav, .aiff, .aif, and .raw files depending on the ouput_file extension. If the extension is not recognized, the format is RAW (no header). We recommand .wav for Windows, and .au for Unix platforms.

To display information about the phoneme set used by the database, type:

mbrola -i fr1/fr1

It displays the phonetic alphabet as well as copyright information about the database.

Option -e makes Mbrola ignore wrong or missing diphone sequences (replaced by silence) which can be quite useful when debugging your TTS. Equivallent to "IGNORE" directive in the initialization file (N.B replace the obsolete ;;E=OFF , unsupported in .pho file).

Optional parameters let you shorten or lengthen synthetic speech and transpose it by providing optional time and frequency ratios:

mbrola -t 1.2 -f 0.8 fr1/fr1 TEST/bonjour.pho bonjour.wav

or its equivalent in the initialization file:

TIME 1.2
FREQ 0.8

for instance, will result in a RIFF Wav file bonjour.wav 1.2 times longer than the previous one (slower rate), and containing speech in which all fundamental frequency values have been multiplied by 0.8 (sounds lower).

You can also set the values of these coefficients directly in a .pho file by adding special escape sequences like :

;; F=0.8
;; T=1.2

You can change the voice characteristics with the -l parameter. If the sampling rate of your database is 16000, indicating -l 18000 allows you to shorten the vocal tract by a ratio of 16/18 (children voice, or women voice depending on the voice you're working on). With -l 10000, you can lengthen the vocal tract by a ratio of 16/10 (namely the voice of a Troll). The same command in an initialization file becomes "VOICE 10000".

Option -v specifies a VolumeRatio which multiplies each output sample. In the example below, each sample is multipliead by 0.7 (the loudness goes down). Warning: setting VolumeRatio too high generates saturation.

mbrola -v 0.7 fr1/fr1 TEST/bonjour.pho bonjour.wav

or add VOLUME 0.7 in an initialization file

The -c option lets you specify which symbol will be used as an escape sequence for comments and commands in .pho files. The default value is the semi-colon ;, but you may want to change this if your phonetic alphabet uses this symbol, like in:

mbrola -c ! fr1/fr1 TEST/test1.pho test2.pho test.wav

equivalent to "COMMENT !" in an initialization file

The -F option lets you specify which symbol will be used to Flush the audio output. The default value is #, you may want to change the symbol like in:

mbrola -F FLUSH_COMMAND fr1/fr1 test.pho test.wav

equivalent to "FLUSH FLUSH_COMMAND" in the initialization file.

Using Pipes

A - instead of command_file or output_file means stdin or stdout. On multitasking machines, it is easy to run the synthesizer in real time to obtain audio output from the audio device, by using pipes.

Renaming and Cloning phonemes

It may happen that the language processing module connected to MBROLA doesn't use the same phonemic alphabet as the voice used. The Renaming and Cloning mechanisms help you to quickly solve such problems (without adding extra CPU load). The only limitation about phoneme names is that they can't contain blank characters.

If, for instance, phoneme "a" in the mbrola voice you use is called "my_a" in your alphabet, and phoneme "b" is called "my_b", then the following command solves the problem:

mbrola -R "a my_a b my_b" fr1/fr1 test.pho test.wav

You can give as many renaming pairs as you want. Circular definition are not a problem -> "a b b c" will rename original [a] into [b] and original [b] into [c] independantly ([a] won't be renamed to [c]).

LIMITATION: you can't rename a phoneme into another that already exists.

The cloning mechanism does exactly the same thing, though the old phoneme still exists after renaming. This is usefull if you have 2 allophones in your alphabet, but the Mbrola voice only provides one.

Imagine for instance, that you make the disctinction between the voiced [r] and its unvoiced counterpart [r0] and that you are using a syllabic version [r=]. If as a first approximation using [r] for both is OK, then you may use an Mbrola voice that only provides one version of [r] by running:

mbrola -C "r r0 r r=" fr1/fr1 test.pho test.wav

which tells the synthesizer that [r0] and [r=] should be both synthesized as [r]. You can write a long cloning list of phoneme pairs to fit your needs.

Renaming and cloning eats CPU since the complete diphone hash table has to be rebuilt, but once the renaming or cloning has occurred there is absolutely NO RELATED PERFORMANCE DROP. So using this feature is more efficient than a pre-processor, though incompatibilities cannot always be solved by a simple phoneme mapping.

Before renaming anything as #, check paragraph 5.4

When you have long cloning and renaming lists, you can conveniently write them into an initialization file according to the following format:

RENAME a my_a
RENAME b my_b
CLONE r r0
CLONE r r=

The obsolete ;; RENAME a my_a can't be used in .pho file anymore, but is correctly parsed in initialization files.

Note to Festival and EN1 users: the consequence of the change above is that you must change the previous call format mbrola en1 en1mrpa ... into mbrola -I en1mrpa en1 ....


On MSDOS/Windows


mbrola fr1/fr1 TEST/bonjour.pho bonjour.wav

Then you can play the RIFF Wav file with windows sound utility or pipes may be used just like below.

On modern Linux

mbrola fr1/fr1 TEST/bonjour.pho | aplay

where aplay is your audio file player (aplay for ALSA paplay for PulseAudio).

If your audioplayer has problems with sun .AU files, try with .raw Never use .wav format when you pipe the ouput (mbrola can't rewind the file to write the audio size in the header). Wav format was not developped for Unix (on the contrary Au format let you specify in the header "we're on a pipe, read until end of file").

On Sun4 or with machines with an old audio interface

Those machines are now quite old and only provide a mulaw 8Khz output. A hack is:

mbrola fr1/fr1 input.pho - | sox -t raw -sw -r 16000 - -t raw -Ub -r 8000 - > /dev/audio

(providing you have the public domain sox utility developed by Ircam). You should hear 'bonjour' without the need to create intermediate files. Note that we strongly recommend that you DON'T use SOX, since its resampling method (linear interpolation) will permanently damage the sound.

On VAX or AXP workstations

To make it easier for users to find MBROLA, you should add the following command to your system startup procedure:


where "disk:[dir]" is the name of the directory you created for the
MBROLA_DIR files. You could also add the following command to your
system login command procedure:


to use the decsound device:

$ MCR DECSOUND - volume 40 -play

See also the MBR_OLA.COM batch file in the UTILITY.ZIP file available from the MBROLA Homepage if you cannot play 16 bits sound files on your machine.

Format of input and output files - Limitations

Phoneme commands

The input file bonjour.pho in the above example simply contains :

; bonjour
_ 51 25 114
b 62
o~ 127 48 170.42
Z 110 53.5 116
u 211
R 150 50 91
_ 91

This shows the format of the input data required by MBROLA. Each line contains a phoneme name, a duration (in ms), and a series (possibly none) of pitch targets composed of two float numbers each : the position of the pitch target within the phoneme (in % of its total duration), and the pitch value (in Hz) at this position.

In order to increase readability, it is also possible to enclose pitch target in parentheses. Hence, the first line of bonjour.pho could be written :

_ 51 (25,114)

it tells the synthesizer to produce a silence of 51 ms, and to put a pitch target of 114 Hz at 25% of 51 ms. Pitch targets define a piecewise linear pitch curve. Notice that the intonation curve they define is continuous, since the program automatically drops pitch information when synthesizing unvoiced phones.

The data on each line is separated by blank characters or tabs. Comments can optionally be introduced in command files, starting with a semi-colon ;. This default can be overrun with the -c option of the command line.

Another special escape sequence ;; allows the user to introduce commands in the middle of .pho files as described below. This escape sequence is also affected by the -c option.

Changing the Freq Ratio or Time Ratio

A command escape sequence containing a line like "T=xx" modifies the time ratio to xx, the same result is obtained on the fundamental frequency by replacing T with F, like in:

;; T = 1.2

Flush the output stream

Note, finally, that the synthesizer outputs chunks of synthetic speech determined as sections of the piecewise linear pitch curve. Phones inside a section of this curve are synthesized in one go. The last phone of each chunk, however, cannot be properly synthesized while the next phone is not known (since the program uses diphones as base speech units). When using mbrola with pipes, this may be a problem. Imagine, for instance, that mbrola is used to create a pipe-based speaking clock on an HP:

speaking_clock | mbrola - | splayer

which tells the time, say, every 30 seconds. The last phone of each time announcement will only be synthesized when the next announcement starts. To bypass this problem, mbrola accepts a special command phone, which flushes the synthesis buffer : "#"

This default character can be replaced by another symbol thanks to the command:

;; FLUSH new_flush_symbol

Another important issue with piping under UNIX, is the possibility to prematurely end the audio output, if for example the user presses the stop button of your application. Since release 3.01, Mbrola handles signals.

If in the previous example the user wants to interrupt the speaking clock message, the application just needs to send the USR1 signal. You can send such a signal from the console with:

kill -SIGUSR1 mbrola_process_number

Once mbrola catches the signal, it reads its input stream until it gets EOF or a FLUSH command (hence, surrounding sections with flush is a good habit).

Limitations of the program

Phones can be synthesized with a maximum duration which depends on the fundamental frequency with which they are produced. The higher the frequency, the lower the duration. For a frequency of 133 Hz, the maximum duration is 7.5 sec. For a frequency of 66.5 Hz, it is 15 sec. For a frequency of 266 Hz, it is 3.75 sec.


Report bugs to MBROLA Issues page on GitHub.

Look at and subscribe to MBROLA mailing list to view and discuss other related topics.


This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more details.

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