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27. Programming

This chapter covers aspects of programming within the Festival environment, creating new modules, and modifying existing ones. It describes basic Classes available and gives some particular examples of things you may wish to add.

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27.1 The source code

The ultimate authority on what happens in the system lies in the source code itself. No matter how hard we try, and how automatic we make it, the source code will always be ahead of the documentation. Thus if you are going to be using Festival in a serious way, familiarity with the source is essential.

The lowest level functions are catered for in the Edinburgh Speech Tools, a separate library distributed with Festival. The Edinburgh Speech Tool Library offers the basic utterance structure, waveform file access, and other various useful low-level functions which we share between different speech systems in our work. See (speechtools)Top section ‘Overview’ in Edinburgh Speech Tools Library Manual.

The directory structure for the Festival distribution reflects the conceptual split in the code.


The user-level executable binaries and scripts that are part of the festival system. These are simple symbolic links to the binaries or if the system is compiled with shared libraries small wrap-around shell scripts that set LD_LIBRARY_PATH appropriately


This contains the texinfo documentation for the whole system. The ‘Makefile’ constructs the info and/or html version as desired. Note that the festival binary itself is used to generate the lists of functions and variables used within the system, so must be compiled and in place to generate a new version of the documentation.


This contains various examples. Some are explained within this manual, others are there just as examples.


The basic Scheme parts of the system, including ‘init.scm’ the first file loaded by festival at start-up time. Depending on your installation, this directory may also contain subdirectories containing lexicons, voices and databases. This directory and its sub-directories are used by Festival at run-time.


Executables for Festival’s internal use. A subdirectory containing at least the audio spooler will be automatically created (one for each different architecture the system is compiled on). Scripts are added to this top level directory itself.


By default this contains the voices used by Festival including their basic Scheme set up functions as well as the diphone databases.


This contains various lexicon files distributed as part of the system.


This contains the basic ‘Makefile’ configuration files for compiling the system (run-time configuration is handled by Scheme in the ‘lib/’ directory). The file ‘config/config’ created as a copy of the standard ‘config/config-dist’ is the installation specific configuration. In most cases a simpel copy of the distribution file will be sufficient.


The main C++/C source for the system.


Where the ‘libFestival.a’ is built.


Where include files shared between various parts of the system live. The file ‘festival.h’ provides access to most of the parts of the system.


Contains the top level C++ files for the actual executables. This is directory where the executable binary ‘festival’ is created.


The main core of the Festival system. At present everything is held in a single sub-directory ‘./src/arc/festival/’. This contains the basic core of the synthesis system itself. This directory contains lisp front ends to access the core utterance architecture, and phonesets, basic tools like, client/server support, ngram support, etc, and an audio spooler.


In contrast to the ‘arch/’ directory this contains the non-core parts of the system. A set of basic example modules are included with the standard distribution. These are the parts that do the synthesis, the other parts are just there to make module writing easier.


This contains some basic simple modules that weren’t quite big enough to deserve their own directory. Most importantly it includes the Initialize module called by many synthesis methods which sets up an utterance structure and loads in initial values. This directory also contains phrasing, part of speech, and word (syllable and phone construction from words) modules.


This is not really a module in the true sense (the Word module is the main user of this). This contains functions to construct, compile, and access lexicons (entries of words, part of speech and pronunciations). This also contains a letter-to-sound rule system.


This contains various intonation systems, from the very simple to quite complex parameter driven intonation systems.


This contains various duration prediction systems, from the very simple (fixed duration) to quite complex parameter driven duration systems.


A basic diphone synthesizer system, supporting a simple database format (which can be grouped into a more efficient binary representation). It is multi-lingual, and allows multiple databases to be loaded at once. It offers a choice of concatenation methods for diphones: residual excited LPC or PSOLA (TM) (which is not distributed)


Various text analysis functions, particularly the tokenizer and utterance segmenter (from arbitrary files). This directory also contains the support for text modes and SGML.


An LPC based diphone synthesizer. Very small and neat.


The Festival/Scheme front end to An XML parser written by Richard Tobin from University of Edinburgh’s Language Technology Group.. rxp is now part of the speech tools rather than just Festival.


A simple interface the the Stochastic Context Free Grammar parser in the speech tools library.


An optional module contain the previouslty used diphone synthsizer.


A partial implementation of a cluster unit selection algorithm as described in black97c.

./src/modules/Database rjc_synthesis

This consist of a new set of modules for doing waveform synthesis. They are inteneded to unit size independent (e.g. diphone, phone, non-uniform unit). Also selection, prosodic modification, joining and signal processing are separately defined. Unfortunately this code has not really been exercised enough to be considered stable to be used in the default synthesis method, but those working on new synthesis techniques may be interested in integration using these new modules. They may be updated before the next full release of Festival.


Other optional directories may be contained here containing various research modules not yet part of the standard distribution. See below for descriptions of how to add modules to the basic system.

One intended use of Festival is offer a software system where new modules may be easily tested in a stable environment. We have tried to make the addition of new modules easy, without requiring complex modifications to the rest of the system.

All of the basic modules should really be considered merely as example modules. Without much effort all of them could be improved.

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27.2 Writing a new module

This section gives a simple example of writing a new module. showing the basic steps that must be done to create and add a new module that is available for the rest of the system to use. Note many things can be done solely in Scheme now and really only low-level very intensive things (like waveform synthesizers) need be coded in C++.

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27.2.1 Example 1: adding new modules

The example here is a duration module which sets durations of phones for a given list of averages. To make this example more interesting, all durations in accented syllables are increased by 1.5. Note that this is just an example for the sake of one, this (and much better techniques) could easily done within the system as it is at present using a hand-crafted CART tree.

Our knew module, called Duration_Simple can most easily be added to the ‘./src/Duration/’ directory in a file ‘simdur.cc’. You can worry about the copyright notice, but after that you’ll probably need the following includes

#include <festival.h>

The module itself must be declared in a fixed form. That is receiving a single LISP form (an utterance) as an argument and returning that LISP form at the end. Thus our definition will start

LISP FT_Duration_Simple(LISP utt)

Next we need to declare an utterance structure and extract it from the LISP form. We also make a few other variable declarations

    EST_Utterance *u = get_c_utt(utt);
    EST_Item *s;
    float end=0.0, dur;
    LISP ph_avgs,ldur;

We cannot list the average durations for each phone in the source code as we cannot tell which phoneset we are using (or what modifications we want to make to durations between speakers). Therefore the phone and average duration information is held in a Scheme variable for easy setting at run time. To use the information in our C++ domain we must get that value from the Scheme domain. This is done with the following statement.

    ph_avgs = siod_get_lval("phoneme_averages","no phoneme durations");

The first argument to siod_get_lval is the Scheme name of a variable which has been set to an assoc list of phone and average duration before this module is called. See the variable phone_durations in ‘lib/mrpa_durs.scm’ for the format. The second argument to siod_get_lval. is an error message to be printed if the variable phone_averages is not set. If the second argument to siod_get_lval is NULL then no error is given and if the variable is unset this function simply returns the Scheme value nil.

Now that we have the duration data we can go through each segment in the utterance and add the duration. The loop looks like

    for (s=u->relation("Segment")->head(); s != 0; s = next(s))

We can lookup the average duration of the current segment name using the function siod_assoc_str. As arguments, it takes the segment name s->name() and the assoc list of phones and duration.

        ldur = siod_assoc_str(s->name(),ph_avgs);

Note the return value is actually a LISP pair (phone name and duration), or nil if the phone isn’t in the list. Here we check if the segment is in the list. If it is not we print an error and set the duration to 100 ms, if it is in the list the floating point number is extracted from the LISP pair.

        if (ldur == NIL)
            cerr << "Phoneme: " << s->name() << " no duration "
                << endl;
            dur = 0.100;
            dur = get_c_float(car(cdr(ldur)));

If this phone is in an accented syllable we wish to increase its duration by a factor of 1.5. To find out if it is accented we use the feature system to find the syllable this phone is part of and find out if that syllable is accented.

        if (ffeature(s,"R:SylStructure.parent.accented") == 1)
            dur *= 1.5;

Now that we have the desired duration we increment the end duration with our predicted duration for this segment and set the end of the current segment.

        end += dur;

Finally we return the utterance from the function.

    return utt;

Once a module is defined it must be declared to the system so it may be called. To do this one must call the function festival_def_utt_module which takes a LISP name, the C++ function name and a documentation string describing what the module does. This will automatically be available at run-time and added to the manual. The call to this function should be added to the initialization function in the directory you are adding the module too. The function is called festival_DIRNAME_init(). If one doesn’t exist you’ll need to create it.

In ‘./src/Duration/’ the function festival_Duration_init() is at the end of the file ‘dur_aux.cc’. Thus we can add our new modules declaration at the end of that function. But first we must declare the C++ function in that file. Thus above that function we would add

LISP FT_Duration_Simple(LISP args);

While at the end of the function festival_Duration_init() we would add

   "(Duration_Simple UTT)\n\
  Label all segments with average duration ... ");

In order for our new file to be compiled we must add it to the ‘Makefile’ in that directory, to the SRCS variable. Then when we type make in ‘./src/’ our new module will be properly linked in and available for use.

Of course we are not quite finished. We still have to say when our new duration module should be called. When we set

   (Parameter.set 'Duration_Method Duration_Simple)

for a voice it will use our new module, calls to the function utt.synth will use our new duration module.

Note in earlier versions of Festival it was necessary to modify the duration calling function in ‘lib/duration.scm’ but that is no longer necessary.

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27.2.2 Example 2: accessing the utterance

In this example we will make more direct use of the utterance structure, showing the gory details of following relations in an utterance. This time we will create a module that will name all syllables with a concatenation of the names of the segments they are related to.

As before we need the same standard includes

#include "festival.h"

Now the definition the function

LISP FT_Name_Syls(LISP utt)

As with the previous example we are called with an utterance LISP object and will return the same. The first task is to extract the utterance object from the LISP object.

    EST_Utterance *u = get_c_utt(utt);
    EST_Item *syl,*seg;

Now for each syllable in the utterance we want to find which segments are related to it.

    for (syl=u->relation("Syllable")->head(); syl != 0; syl = next(syl))

Here we declare a variable to cummulate the names of the segments.

        EST_String sylname = "";

Now we iterate through the SylStructure daughters of the syllable. These will be the segments in that syllable.

        for (seg=daughter1(syl,"SylStructure"); seg; seg=next(seg))
            sylname += seg->name();

Finally we set the syllables name to the concatenative name, and loop to the next syllable.


Finally we return the LISP form of the utterance.

    return utt;

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27.2.3 Example 3: adding new directories

In this example we will add a whole new subsystem. This will often be a common way for people to use Festival. For example let us assume we wish to add a formant waveform synthesizer (e.g like that in the free ‘rsynth’ program). In this case we will add a whole new sub-directory to the modules directory. Let us call it ‘rsynth/’.

In the directory we need a ‘Makefile’ of the standard form so we should copy one from one of the other directories, e.g. ‘Intonation/’. Standard methods are used to identify the source code files in a ‘Makefile’ so that the ‘.o’ files are properly added to the library. Following the other examples will ensure your code is integrated properly.

We’ll just skip over the bit where you extract the information from the utterance structure and synthesize the waveform (see ‘donovan/donovan.cc’ or ‘diphone/diphone.cc’ for examples).

To get Festival to use your new module you must tell it to compile the directory’s contents. This is done in ‘festival/config/config’. Add the line

ALSO_INCLUDE += rsynth

to the end of that file (there are simialr ones mentioned). Simply adding the name of the directory here will add that as a new module and the directory will be compiled.

What you must provide in your code is a function festival_DIRNAME_init() which will be called at initialization time. In this function you should call any further initialization require and define and new Lisp functions you with to made available to the rest of the system. For example in the ‘rsynth’ case we would define in some file in ‘rsynth/

#include "festival.h"

static LISP utt_rtsynth(LISP utt)
    EST_Utterance *u = get_c_utt(utt);
    // Do format synthesis 
    return utt;

void festival_rsynth_init()

   "(Rsynth_Synth UTT)
   A simple formant synthesizer");


Integration of the code in optional (and standard directories) is done by automatically creating ‘src/modules/init_modules.cc’ for the list of standard directories plus those defined as ALSO_INCLUDE. A call to a function called festival_DIRNAME_init() will be made.

This mechanism is specifically designed so you can add modules to the system without changing anything in the standard distribution.

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27.2.4 Example 4: adding new LISP objects

This third example shows you how to add a new Object to Scheme and add wraparounds to allow manipulation within the Scheme (and C++) domain.

Like example 2 we are assuming this is done in a new directory. Suppose you have a new object called Widget that can transduce a string into some other string (with some optional continuous parameter). Thus, here we create a new file ‘widget.cc’ like this

#include "festival.h"
#include "widget.h"  // definitions for the widget class

In order to register the widgets as Lisp objects we actually need to register them as EST_Val’s as well. Thus we now need


The first names given to these functions should be a short mnenomic name for the object that will be used in the defining of a set of access and construction functions. It of course must be unique within the whole system. The second name is the name of the object itself.

To understand its usage we can add a few simple widget manipulation functions

LISP widget_load(LISP filename)
   EST_String fname = get_c_string(filename);
   Widget *w = new Widget;   // build a new widget

   if (w->load(fname) == 0)  // successful load
      return siod(w);
      cerr << "widget load: failed to load \"" << fname << "\"" << endl;
   return NIL;  // for compilers that get confused

Note that the function siod constructs a LISP object from a widget, the class register macro defines that for you. Also note that when giving an object to a LISP object it then owns the object and is responsible for deleting it when garbage collection occurs on that LISP object. Care should be taken that you don’t put the same object within different LISP objects. The macros VAL_RESGISTER_CLASS_NODEL should be called if you do not want your given object to be deleted by the LISP system (this may cause leaks).

If you want refer to these functions in other files within your models you can use


in a common ‘.h’ file

The following defines a function that takes a LISP object containing a widget, applies some method and returns a string.

LISP widget_apply(LISP lwidget, LISP string, LISP param)
    Widget *w = widget(lwidget);
    EST_String s = get_c_string(string);
    float p = get_c_float(param);
    EST_String answer;

    answer = w->apply(s,p);

    return strintern(answer);

The function widget, defined by the registration macros, takes a LISP object and returns a pointer to the widget inside it. If the LISP object does not contain a widget an error will be thrown.

Finally you wish to add these functions to the Lisp system

void festival_widget_init()
    "(widget.load FILENAME)\n\
  Load in widget from FILENAME.");
    "(widget.apply WIDGET INPUT VAL)\n\
  Returns widget applied to string iNPUT with float VAL.");

In your ‘Makefile’ for this directory you’ll need to add the include directory where ‘widget.h’ is, if it is not contained within the directory itself. This is done through the make variable LOCAL_INCLUDES as

LOCAL_INCLUDES = -I/usr/local/widget/include

And for the linker you’ll need to identify where your widget library is. In your ‘festival/config/config’ file at the end add

COMPILERLIBS += -L/usr/local/widget/lib -lwidget

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