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Voice Database Format

The voice database format (*.vdb) is an on-disk file format used by Cainteoir Text-to-Speech to store the information needed for a synthetic voice to produce audio when given phoneme and prosodic information. This format acts as a container for different voice formats in a form suitable for reading directly from the file.

Data Types

| u8 | An 8-bit unsigned integer | | u16 | A 16-bit unsigned integer | | u32 | A 32-bit unsigned integer | | u64 | A 64-bit unsigned integer | | f8:8 | A fixed point number (8-bit integral part, 8-bit fraction part) | | f16:16 | A fixed point number (16-bit integral part, 16-bit fraction part) | | str | A variable-length UTF-8 string terminated by a NULL (0) character | | pstr | A u32 containing the offset from the start of the file to a str. |

Structure

The voice database file has the following general structure:

Header
Section
...
Section

A String Table section follows any section (including the Header section) that contains pstr values.

The specific layout is dependent on the synthesizer type.

MBROLA

These files describe how Cainteoir Text-to-Speech phonemes are mapped to the MBROLA PHO file format and the voice-specific phonemes. This is then sent to the mbrola program to synthesize using the MBROLA voice database file.

The id in the Header section is the name of the MBROLA voice database file to use.

A Duration Table section is used to specify the duration model to be used.

The Phoneme Table and Phoneme Unit Table sections map Cainteoir Text-to-Speech phonemes to the voice-specific MBROLA phonemes.

The Pitch Data section specifies the mean and standard deviation of the voice's pitch.

Header

The header section identifies the file as a VoiceDB file and provides information about the voice. This information is used to construct the RDF metadata associated with the voice.

Field Type Offset
magic u8[7] 0
endianness u16 7
rdfns pstr 9
id pstr 13
name pstr 17
synthesizer pstr 21
author pstr 25
locale pstr 29
gender u8 33
volume-scale f8:8 34
frequency u16 36
channels u8 38
sample-format pstr 39
END OF HEADER 43

The magic field identifies the file as a voice database file. This is the string "VOICEDB".

The endianness field contains the value 0x3031. It is used to identify whether the file is in little endian (10) or big endian (01) order.

The rdfns field contains the URI used as the RDF namespace for generated RDF metadata. It is also the URI associated with information about the synthesizer.

The id field is the programatic identifier used to reference the voice. Any RDF metadata associated with the voice will be associated with rdfns:id.

The name field is the name of the voice that will be displayed to the user.

The synthesizer field is the name of the synthesizer this voice uses. This is used to select the synthesis algorithm, as well as being displayed to the user.

The author field is the name of the authors/companies that created the voice.

The locale field is the name of the BCP 47 language code for the default language and accent supported by the voice.

The gender field is the gender of the voice, with M used for male voices and F used for female voices.

The volume-scale field is the value used to scale the audio to 0.5 on a scale of 0.0 to 1.0. This represents 100% volume.

Pitch Data

This provides information about the fundamental frequency (F0) of the voice, used to determine the pitch envelopes of the different phonemes. It describes the default speaking pitch of the voice.

Field Type Offset
magic u8[3] 0
baseline f16:16 3
step f16:16 7
sdev f16:16 11
END OF HEADER 15

The magic field identifies the file as a voice database file. This is the string "PTC".

The baseline field is the average low pitch of the voice in Hertz. That is, this represents the lowest pitch the voice is comfortable speaking.

The step field is the frequency gap between each tone levels.

The sdev field is the standard deviation of the pitch around each tone level in Hertz.

This model is used as it can be adapted to the different prosody algorighms.

To calculate the average pitch for the IPA tone levels, you can use the following:

  • Top Tone = baseline + 4*step
  • High Tone = baseline + 3*step
  • Mid Tone = baseline + 2*step
  • Low Tone = baseline + step
  • Bottom Tone = baseline

To use the INTSINT prosody model, T is the Top Tone, M is the Mid Tone and B is the Bottom Tone.

The baseline, step and sdev values can be derived from a minimum (min) and maximum (max) pitch value, such that:

  • sdev = (max - min)/ 20
  • baseline = min + 2*sdev
  • step = 4 *sdev

This is because there are 5 tone levels, each with 4 sdev sections, with 2 sdev sections either side of the mean value of each tone level.

Data Table

This is the generic structure of a tabular section. That is, a fixed sized array of entities of the same type.

Field Type Offset
magic u8[3] 0
num-entries u16 3
END OF SECTION 5

The magic field identifies the section as a data table. See the sub-sections for the actual value.

The num-entries field is the number of entries there are in this table.

After the section block, num-entries entry blocks are written out in order. An associated String Table section occurs after the last entry, with the pstr strings from all the entry blocks included.

Duration Table

This is the binary representation of a (mean, standard-deviation) duration model.

A duration table has the "DUR" magic string, and each entry has the form:

Field Type Offset
phoneme1 u64 0
phoneme2 u64 8
duration-mean u8 16
duration-stdev u8 17
END OF ENTRY 18

The phoneme1 field is the value of the phoneme as represented by the cainteoir::ipa::phoneme class.

The phoneme2 field is the value of the phoneme as represented by the cainteoir::ipa::phoneme class. This is for affricates and diphthongs.

Theduration-mean field is the average duration of the phoneme in milliseconds.

Theduration-stdev field is the standard deviation for the duration of the phoneme in milliseconds.

Phoneme Unit Table

This is the information about how a given unit should be constructed when synthesizing the associated phoneme.

A phoneme unit table has the "PUT" magic string, and each entry has the form:

Field Type Offset
name pstr 0
phoneme-start u8 4
unit-start u8 5
unit-end u8 6
END OF ENTRY 7

The name field is the name of the unit as used to select the unit in the phone or diphone synthesis.

The phoneme-start field is the percentage offset of the phoneme at which this unit is generated. The end of the phoneme is the phoneme-start of the next unit in the sequence, or 100% if this is the last unit.

The unit-start field is the percentage offset at which this unit starts. This allows for partial units to be synthesized.

The unit-end field is the percentage offset at which this unit ends. This allows for partial units to be synthesized.

Phoneme Table

This is the information for how to map phonemes to units in unit-based phoneme synthesis.

A phoneme table has the "PHO" magic string, and each entry has the form:

Field Type Offset
phoneme1 u64 0
phoneme2 u64 8
first-unit u16 16
num-units u8 18
END OF ENTRY 19

The phoneme1 field is the value of the phoneme as represented by the cainteoir::ipa::phoneme class.

The phoneme2 field is the value of the phoneme as represented by the cainteoir::ipa::phoneme class. This is for affricates and diphthongs.

The first-unit field is the index of the first unit in the Phoneme Unit Table.

Thenum-units field is the number of sound units this phoneme is composed of.

String Table

A string table is a data table that does not contain a num-elements field. Instead, it contains an offset to the start of the next section. Each entry is a str value that is referenced by a pstr field in the previous section.

This is designed to make it easy to traverse over the variable-length string data.

It has the form:

Field Type Offset
magic u8[3] 0
next-section u32 3
END OF SECTION 7

The magic field identifies the section as a data table. This is the string "STR".

The next-section field is the offset to the next data block.

Magic Values

This is the list of 3-letter magic values used to identify the different section and table types. This list is non-normative and is useful when creating a new section type to avoid collisions in the magic values.

Magic Usage
DUR Duration Table
PHO Phoneme Table
PTC Pitch Data
PUT Phoneme Unit Table
STR String Table

Copyright (C) 2014 Reece H. Dunn