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MBROLA database creation tool

This guide describes how to create voice database for the MBROLA speech synthesizer.

General steps

PHASE 0: compile tools

  1. Compiling MBE analysis

    1. in AnaMBE directory, type make
    2. you get some warnings about conversion from int to double, hopefully nothing lethal.
    3. resulting binaries Obj/anaf0 Obj/anambe must be copied with root privilege under /usr/local/bin (or any other searchable path).

  2. Compile resynthesis and database_build

    1. in Resynthesis directory, type make
    2. copy resynth* and database_build binaries in /usr/local/bin (or any other searchable path).

  3. Then you need to know about the diphone provider instruction file... because here you're going to compile what the diphone provider gives you.

PHASE 1: check the data

you need audio file encoded as linear 16 bits, 16khz, little endian (PC format), and a text segmentation file containing something that looks like:

file name
|        diphone name
|       |        first sample
|       |        |     last sample
v       |        |     |      middle sample
        V        V     V      v
##a.d16	_ a	2000	3910	2929
ak.d16	a k	2000	4027	2939
i#.d16	i _	2000	4654	3228
ki.d16	k i	2000	3882	3150

First source of problems: names in the .seg file and file names do not correspond well — uppercase and lowercase sometimes need to be updated by yourself or by the provider.

Second source of problems: strange diphone names — for example, silence better be "_", rather than "#" (which is Flush character). Although it can be parametrized under mbrola it's looking for trouble.

Third source of problems: people sometimes mess up segmentation boundaries order, or they write bytes instead of samples — whatever, it will generate an error later.

Fourth source of problems: if diphone _-_ (silence silence) is provided it must be the last diphone of the database in the seg file. But generally it is advised to remove that phoneme as it is looking for trouble (MBE analysis dies on numeric silence).

Fifth source of problems mentioned above: never never never introduce any numeric silence (sequence of 0). First absolute 0 are not natural, second anambe crashes badly trying to compute infinite decibel spectral slices...

PHASE 2: generate analysis parameter files

If we have audio files in a directory, say WAV directory for example, and br1w5.seg segmentation file. Final database's name will be br1w5. One has to build different parameter files for speech analysis:

generate_mbrola br1w5

will automatically build "default" files:

-rw-r--r--   1 user    program       44 Jul 25 11:24 br1w5.f0
-rw-r--r--   1 user    program       52 Jul 25 11:24 br1w5.mbe
-rw-r--r--   1 user    program       91 Jul 25 11:24 br1w5.syn

They resp. contain data for three different analysis:

  1. f0 analysis (pitch, with anaf0 binary) br1w5.f0
  2. harmonic/noise analysis (MBE model with anambe binary) br1w5.mbe
  3. mbrola format frame resynthesis (resynth binary) br1w5.syn

In a first approach keep default values, only mbe and syn need be changed in the following. Let's do it now for mbe — listen to some of your audio files to get an idea of speaker's average pitch, then measure the length of 1 pitch period in samples (for example using wavesurfer or any audio editor you like). E.g. on the brazilian voice we find 144 samples (i.e. a 90Hz pitch), so edit .mbe file

Nfft=1024
Freq=16000
FrameLength=360
FrameShift=120

Replace FrameShift field with 144, and FrameLength field with 144*3 (it's empirical but it works!) that is 432.

PHASE 3: generate the makefile

Three analysis (f0, mbe, resynthesis) are done on each audio file and generate an s16 result. To avoid manual handling on updates of segmentation use make or pmake (historical reason: in 1996 Mbrola analysis was quite slow on 1 machine, hence pmake was used to distribute analysis/resynthesis of a database on several Unix machines while we were having a beer on the Grand Place of Mons).

generate_make.pl br1w5 WAV/ RES/ RES/

will generate br1w5.mak that's gonna use audio files in WAV/ (don't forget the slash), and put result and intermediate files in RES/.

Example of a block in the mak file:

RES/0.f0 : WAV/1.d16 test.f0
        anaf0 'WAV/1.d16' RES/0.f0 2000 3810 test.f0
RES/0.mbe: RES/0.f0 test.mbe
        anambe WAV/1.d16 RES/0.f0 RES/0.mbe 2000 3810 test.mbe
RES/0.s16 : RES/0.mbe test.syn
         resynth WAV/1.d16 RES/0.mbe RES/0 test.syn

This block describes the construction of 0.f0 , 0.mbe and 0.s16 files from WAV/1.d16 and parameters in br1w5.f0 br1w5.mbe br1w5.syn.

PHASE 4: execute makefile

make -f br1w5.mak

Some errors might occur — one of the major reason for errors is insufficient audio context for a diphone. I usually ask for 800 samples for safety, but some smart guys sometimes provide shorter context, as a result, even though segmentation boundaries are inside of the wav file, due to the size of analysis windows, it's reading outside. Solution: either shorten the diphone a little bit, either send a note to the provider for a greater audio context (and come on, audio context doesn't mean adding silence on both sides, wicked idea...)

PHASE 5: test the result

Usually make command ends with a line like:

database_build br1w5 RES/ 2.069 16000 144 1

If no - diphone was provided, database_build automatically includes one. No worry. If you have a br1w5.info text file in the directory, it is included at the end of the database as provider's data (can be read with mbrola -i).

Yes, yes you can now test an audio output!

mbrola br1w5 TEST/testw1.pho test.wav

Voila! It should sound ok. Now, one can do fine tuning.... one can set voiced/unvoiced ratios in resynthesis .syn parameters:

Freq=16000
LastPhaseReset=10
VUVLimTra=0.55
VUVLimVoiced=1.2
ElimTrans=5e8
ElimVoiced=5e8

Mainly ElimTrans and ElimVoiced have the same value, and indicate energy level below which we consider we have silence (if the database dynamic is weak one has to lower this value).

VUVLimVoiced is the main parameter to tune voiced/unvoiced effect (if the database is over-voiced, for example you may spot that /S/ is voiced).

VUVLimTra tune smoothing level — the higher, the more mbrola's going to smooth (even when it's harmfull, e.g. between two parts of a /b/). This value corresponds to "transition threshold" — when we declare that an MBE frame is a transition it means "no smoothing beyond" (e.g. plosives, sonorant where formants move quickly).

When you modify .syn parameters, simply launch make again — you'll notice everything goes faster because .f0 and .mbe files are not recomputed (mbe analysis is by far the most greedy part of the process).

If you modify the segmentation boundaries of a diphone, simply execute touch WAV/my_file.wav on corresponding audio file to force make rebuild of its parameters.

There's a special "resynth_debug" version of "resynth" binary that generates .m and .mm matlab files. It displays under matlab f0 and mbe coefficients which comes handy to set sound thresholds.

Another special version is "resynth_female", to process high female pitches — edit .mbe param file to double analysis frame length (goes 1 harmonic higher), edit .mak file to use resynth_female instead of resynth_male and launch make. What happens next? During resynthesis, pitch is doubled (analysis frame was multiplied by 2, then pitch is divided by 2). At the same time, when doubling the pitch, I associate phases with their correct harmonic, and duplicate them for odd harmonics (one has to invent phases for those harmonics).

PHASE 6: debugging?

listen to your mbrola output to track any over/under smoothing on unvoiced/voiced plosives or fricatives.

You're all set.

ADDENDUM:

Downsampling a database... Edit .mak to use resynth_resample instead of resynth (filter can be modified in Resynthesis/Src/COEF_FILTER depending on target freq). Actually every .s16 file is downsampled into a .s10 file.

You may also to modify the make file:

database_build br1w5 RES/ 2.060 16000 144 1

becomes:

database_build br1w5 RES/ 2.060 8000 77 1 16000

AVAILABLE RESAMPLING: 16khz to 8khz (resynth_resample16_8, works for every 1/2 ratios, e.g. from 22050 to 11025), and 22050Hz to 8000Hz with resynth_resample22_8

22Khz databases!!!!

It's the hack of the hack... never try to replace 16000 parameters in your .mbe or .f0 or .syn files, it could make sense, but it's a trap. All those programs were handcrafted a very long time ago by Thierry Dutoit and everything has been designed for 16000Hz (some band pass filters inside, some frequency dependent obscure constants).

The hack of the hack is: don't touch anything, pretend you work at 16000Hz on 22050Hz files (you get quite long periods generally but who cares). Simply indicate real sample rate at the very last minute on "database_build".

running on windows....

Well, what does it take to run this on windows? Well either Cygwin tools :-)

Or simply modify generate_make.pl so that instead of building a .mak with dependencies between files, it builds a .bat with explicit commands. Nowadays building a mbrola database is a cinch for any PC, which renders usage of .mak somehow obsolete (it used to be elegant).