Microsoft Speech API 5.1 support for CMU Flite
----------------------------------------------
Copyright Cepstral, LLC, 2001 all rights reserved
David Huggins-Daines <dhd@cepstral.com>
December 6th, 2001
About the Flite SAPI port
-------------------------
Funding for this work was provided by the Instituto de Engenharia de
Sistemas e Computadores (Lisbon, Portugal). The port itself was done
by David Huggins-Daines at Cepstral, LLC (Pittsburgh, USA).
This work remains Copyright Cepstral, LLC but is distributed under
the same free software licence as CMU Flite.
What's here
-----------
This directory contains a port of CMU Flite 1.1 and the included 8kHz
diphone voice to the Win32 platform under Visual C++, as well as an
interface library that allows Flite voices to be compiled into COM
objects which implement the TTS engine interfaces for Microsoft's
Speech API 5.1 (SAPI).
What isn't here
---------------
There isn't a pointy-clicky tool for automatically converting voices
to SAPI objects. You are more than welcome to write one; it should be
fairly straightforward to do as a Visual Studio wizard or add-in or
whatever they call those things.
Instead, the procedure for making SAPI objects is documented below.
Feel free to ask me questions at the address above if you don't
understand some parts of it.
Some parts of the SAPI interface code are language specific, namely
the viseme and phoneme translation code, and to some extent the text
processing code. These have been implemented for US English only,
although the relevant functions are abstracted with function pointers
so each voice is free to choose its own. See "Language-Specific
Functions" below for more information.
Building and testing the example voice
--------------------------------------
In order to build the Flite SAPI code and example diphone voice, you
will need a copy of Visual C++ 6.0 or later, as well as the full SDK
for SAPI 5.1. If you have the Microsoft Platform SDK, you will need
to make sure to install the Internet Explorer SDK as well, as it
contains some IDL files that are required in order to build COM
objects with the Platform SDK.
Before you build anything, you will need to set up Visual C++ to find
the SAPI header and IDL files. To do this, select "Options" from the
"Tools" menu. In the resulting dialog box, switch to the
"Directories" tab. Now, add the "include" and "IDL" directories from
your SAPI SDK installation to the list. If you performed a default
installation of the SAPI SDK on the C: drive, they will be:
C:\Program Files\Microsoft Speech SDK 5.1\Include
C:\Program Files\Microsoft Speech SDK 5.1\IDL
Make sure the build type is set to "Win32 - Debug" in Visual C++. Set
the active project to "FliteCMUKalDiphone". Select "Build
FliteCMUKalDiphone.dll" from the "Build" menu. This will build all of
the other libraries before building the SAPI object.
The first time you use the voice, you will need to register it with
Windows. To do this, build the "register_vox" project and execute
register_vox.exe (you can find it in the
FliteCMUKalDiphone\register_vox\Debug subdirectory, or you can simply
run it from within Visual C++).
Although, normally, Visual C++ should automatically register the
FliteCMUKalDiphone object as a COM server, in some cases you may have
to do it manually. This can be done by running 'regsvr32
FliteCMUKalDiphone.dll' on the command-line from the build directory
(sapi\FliteCMUKalDiphone\Debug).
Now you can test the voice by running the SAPI "TTSApp" example
program, or any of the other examples included with the SAPI SDK.
How to SAPI-enable your own Flite voices
----------------------------------------
First, you'll obviously need to build your voice under Visual C++.
This is relatively straightforward. It's probably best to build it as
a static library. You'll need to make sure that it can find the Flite
header files as well as the ones for your language and lexicon, which
probably means adding their paths in the "Preprocessor" category of
the "C/C++" tab of the Project Settings dialog box.
One thing to be aware of is that the Microsoft linker will probably
break if you have very large voice data files as C code. To work
around this problem, you can change "Debug Info" from "Program
Database for Edit and Continue" to "Program Database" in the "General"
category of the "C/C++" tab in the Project Settings dialog box.
Since there is no support for dynamically discovering and loading
voices in Flite, each SAPI voice links to its own instance of the
engine. This also simplifies the distribution and installation of
voices considerably.
The common code used to implement the SAPI interface is in the
FliteTTSEngineObj library. Your voice should create a subclass of
CFliteTTSEngineObj. In the minimal case, you only need to provide a
constructor that sets the 'regfunc' and 'unregfunc' members of the
base class to the registration and unregistration functions defined in
your Flite voice.
To set up the voice object, create a new Visual C++ project, using the
project type "ATL COM AppWizard". For "Server Type", choose "Dynamic
Link Library (DLL)".
Now you must create a definition for the voice object. To do this,
switch to "ClassView" in the sidebar, right-click on the project name,
and choose "New ATL Object...". Then, from the selection box, choose
"Simple Object".
In the "Names" tab of the next dialog box ("ATL Object Wizard
Properties"), choose whatever names you like for your class. In the
"Attributes" tab, select "Both" in the "Threading Model" section, and
"Custom" in the "Interface" section.
Next, you need to edit the IDL file to import and use the relevant
SAPI interfaces. You should be able to find this file in the "Source
Files" section of your new project in the "FileView" tab in the
sidebar. If your project name was "FooVoice", the IDL file will be
called "FooVoice.idl". In order to import the SAPI interfaces, you
should add the following line to the list of 'import' statements at
the top of the file:
import "sapiddk.idl";
In order for Visual C++ to find this import, you will have to add the
SAPI IDL directory it to the Tools->Options dialog box as detailed
above (do not add it to the Project Settings, because MIDL.EXE is
broken and will not accept it.)
Just underneath the list of import statements, Visual C++ will have
created a bogus interface definition for your object, which will look
like this (the UUID and interface name will be different, of course):
[
object,
uuid(51284204-38B4-48C4-B65E-4FDAF6476D13),
helpstring("IFooVoiceObj Interface"),
pointer_default(unique)
]
interface IFooVoiceObj : IUnknown
{
};
You should delete this section. Then, you should change the list of
interfaces in the 'coclass' section to use the SAPI TTS Engine
interfaces. It should look like this (replace "FooVoiceObj" with the
name of your voice object):
coclass FooVoiceObj
{
[default] interface ISpTTSEngine;
interface ISpObjectWithToken;
};
Now you will need to edit the source code for your voice object. As
noted above, in the minimal case, you will simply need to include
"voxdefs.h" from your voice library, inherit from CFliteTTSEngineObj,
provide declarations for REGISTER_VOX and UNREGISTER_VOX, and
initialize the pointers to them in a constructor.
To do this, open the header file for your voice object. It can be
found in the "Header Files" section for your project in the "FileView"
tab in the sidebar. If your voice object name (as entered in the
"Names" tab in the "ATL Object Wizard Properties" dialog box above)
was "FooVoiceObj", then this file will be called
"FooVoiceObj.h".
First, add these declarations underneath the #include statements at
the top of the file:
#include "FliteTTSEngineObj.h"
#include "flite_sapi_usenglish.h"
extern "C" {
#include "voxdefs.h"
cst_voice *REGISTER_VOX(const char *voxdir);
void UNREGISTER_VOX(cst_voice *vox);
};
You will need to either put the full path to voxdefs.h in the #include
statement, or add the directory containing your voice's source code to
the list of extra include directories in the "Preprocessor" category
of the "C/C++" tab of the Project Settings dialog box. You may also
need to do the same for "FliteTTSEngineObj.h" (if you create your
voice within the "flite_sapi" workspace included here, you can enter
"..\FliteTTSEngineObj" here).
Next, you must adjust the inheritance list for your voice's class.
Remove the following lines marked with '-' and add the line marked
with '+':
- public CComObjectRootEx<CComMultiThreadModel>,
public CComCoClass<CFooVoiceObj, &CLSID_FooVoiceObj>,
- public IFooVoiceObj
+ public CFliteTTSEngineObj
You must also change the COM interface map to contain the SAPI
interfaces, by making the following changes (as above, remove the
lines marked with '-' and add those marked with '+'):
BEGIN_COM_MAP(CFooVoiceObj)
- COM_INTERFACE_ENTRY(IFooVoiceObj)
+ COM_INTERFACE_ENTRY(ISpTTSEngine)
+ COM_INTERFACE_ENTRY(ISpObjectWithToken)
END_COM_MAP()
Finally, add code to the constructor to set the 'regfunc' and
'unregfunc' members, and the language-specific functions, if you have
them, by adding the lines marked with '+':
public:
CFooVoiceObject() {
+ regfunc = REGISTER_VOX;
+ unregfunc = UNREGISTER_VOX;
+ phonemefunc = flite_sapi_usenglish_phoneme;
+ visemefunc = flite_sapi_usenglish_viseme;
+ featurefunc = flite_sapi_usenglish_feature;
+ pronouncefunc = flite_sapi_usenglish_pronounce;
}
Before you build the SAPI object, you will need to add the voice
library and the Flite libraries (flite.lib, plus the libraries for the
lexicon and language model, which are cmulex.lib and usenglish.lib for
US English) to the list of extra libraries (in the "Input" section of
the "Linker" tab of the Project Settings dialog box in Visual C++).
You also need to include "winmm.lib" here as it is required by the
Flite library. You'll also need to make sure that Visual C++ can find
the Flite libraries - you can either set their projects up as
dependencies of your SAPI object's project, or you can add a list of
relative paths to their build directories in the Project Settings.
Registering and testing your new SAPI voice object
--------------------------------------------------
Now that you've built your voice as a SAPI component, you must
register it with the system so that it can be found and used by
programs using the SAPI interface. Predictably, this involves
twiddling bits in the Windows Registry.
Source code and a Visual C++ project is provided (in register-vox.cpp)
for a small command-line program which performs the necessary
operations for the CMU diphone voice. To use it for another voice,
you will need to make the modifications noted by /* CHANGEME */
comments in the source code.
To test your SAPI voice, use the TTSApp program included with the SAPI
SDK. You may find it helpful to build the debugging version of TTSApp
from source code and specify it as the executable to run when
debugging for your SAPI object's project. This will allow you to set
breakpoints in your code and get proper backtraces and so forth.
Language-specific functions
---------------------------
The language-specific functions for US English are contained in the
files flite_sapi_usenglish.c and flite_sapi_usenglish.h. The SAPI
object is set up to use them by initializing four function pointers
which are members of class CFliteTTSEngineObj:
int (*phonemefunc)(cst_item *s);
This function takes a cst_item representing a single phone (usually a
member of the "Segment" relation) and returns the appropriate SAPI
phone ID for it.
int (*visemefunc)(cst_item *s);
This function takes a cst_item representing a single phone and returns
the appropriate SAPI viseme ID for it. The SAPI visemes are
potentially language independent, though they are expressed in the
documentation in terms of US English phonemes. A more general
description of them is included below.
SP_VISEME_0 silence
SP_VISEME_1 low mid/front unrounded vowels (ae, ah, ax)
SP_VISEME_2 low back unrounded vowels (aa)
SP_VISEME_3 low/mid-low back rounded vowels (ao)
SP_VISEME_4 mid front unrounded vowels (eh, ey)
SP_VISEME_5 English mid rhotic vowel (er)
SP_VISEME_6 high front unrounded vowels and glides (ih, iy, y)
SP_VISEME_7 high back rounded vowels and glides (uw, w)
SP_VISEME_8 rounded-to-rounded rising diphthongs (ow)
SP_VISEME_9 unrounded-to-rounded rising diphthongs (aw)
SP_VISEME_10 rounded-to-unrounded rising diphthongs (oy)
SP_VISEME_11 unrounded-to-unrounded rising diphthongs (ay)
SP_VISEME_12 English glottal fricative (hh)
SP_VISEME_13 English retroflex approximant (r)
SP_VISEME_14 English lateral approximant (l)
SP_VISEME_15 grooved alveolar/dental fricatives (s, z)
SP_VISEME_16 palatal fricatives and affricates (sh, zh, ch, jh)
SP_VISEME_17 interdental fricatives (th, dh)
SP_VISEME_18 labiodental fricatives (f, v)
SP_VISEME_19 alveolar/dental occlusives (d, t, n)
SP_VISEME_20 velar occlusives (k, g, ng)
SP_VISEME_21 bilabial occlusives (p, b, m)
When adapting them to your phoneset, remember that the position of the
lips and teeth as viewed from the front is more important than the
place or manner of articulation /per se/.
Also, while the US English code implements this using a table lookup,
it may be more appropriate to determine them algorithmically from the
feature values used in your phoneset.
int (*featurefunc)(cst_item *s);
This function returns a bitmask used by SAPI to indicate placement of
stress or emphasis (see the pages on the SPEVENTENUM and SPVFEATURE
enumerations in the SAPI documentation for more information on this).
If you use "stressed" and "accented" as the feature names for these
things in your language code, you can just copy
flite_sapi_usenglish_feature().
cst_val *(*pronounce_func)(SPPHONEID *spids);
This function takes a zero-terminated array of SAPI phone identifiers
and converts it to a list of cst_val containing the phone names as
used by Flite as strings. You will probably want to simply copy
flite_sapi_usenglish_pronounce(), changing the tables it uses to look
up phone names.
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