FEDL2250DIGEST-09
OKI Semiconductor
ML2250 family
Voice Synthesis Algorithm
The ML2250 family contains 5 algorithm types to match the characteristic of playback voice: 2-bit ADPCM 2
algorithm, 4-bit ADPCM 2 algorithm, 8-bit PCM algorithm, 8-bit non-linear PCM algorithm, and 16-bit PCM
algorithm.
Key feature of each algorithm is described in the table below.
Voice synthesis algorithm
Applied waveform
Feature
Oki’s specific speech synthesis algorithm of low
bit rate with improved 2-bit ADPCM.
Oki’s specific speech synthesis algorithm of
improved waveform follow-up with improved
4-bit ADPCM.
Oki 2-bit ADPCM2
Normal voice waveform
Oki 4-bit ADPCM2
Normal voice waveform
High-frequency
inclusive sound effect etc.
components Algorithm which plays back mid-range of
Oki 8-bit Nonlinear PCM
8-bit PCM
waveform as 10-bit equivalent voice quality.
High-frequency
inclusive sound effect etc.
components
Normal 8-bit PCM algorithm
High-frequency
inclusive sound effect etc.
components
16-bit PCM
Normal 16-bit PCM algorithm
Memory Allocation and Creating Voice Data
The ROM is partitioned into 4 data areas: voice (i.e., phrase) control area, test area, voice area, and phrase control
table area.
The voice control area manages the ROM’s voice data. It controls the start/end addresses of voice data, usage/not
usage of the phrase control table function and so on. The voice control area stores voice control data for 256
phrases.
The test area stores the data for testing.
The voice area stores the actual waveform data.
The phrase control table area stores data for effective use of voice data. As for the details, please refer to the Phrase
Control Table Function.
There is no phrase control table area if the phrase control table is not used.
The ROM data is created using a development tool.
ROM Addresses (ML2252)
0x00000
Voice control area
(16 Kbit Fixed)
0x007FF
0x00800
Test area
0x00807
0x00808
Voice area
max: 0x1FFFF
Phrase Control Table area
Depends on creation of ROM
data.
max: 0x1FFFF
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