FEDL2240DIGEST-02

OKI Semiconductor

ML2240 Family

17/24

Voice Synthesis Algorithm

The ML2240 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 2-bit ADPCM2

Normal voice waveform

Oki’s specific speech synthesis algorithm of low

bit rate with improved 2-bit ADPCM.

Oki 4-bit ADPCM2

Normal voice waveform

Oki’s specific speech synthesis algorithm of

improved waveform follow-up with improved

4-bit ADPCM.

Oki 8-bit Nonlinear PCM

High-frequency components

inclusive sound effect etc.

Algorithm which plays back mid-range of

waveform as 10-bit equivalent voice quality.

8-bit PCM

High-frequency components

inclusive sound effect etc.

Normal 8-bit PCM algorithm

16-bit PCM

High-frequency components

inclusive sound effect etc.

Normal 16-bit PCM algorithm

Memory Allocation and Creating Voice Data

The ROM is partitioned into 3 data areas: voice (i.e., phrase) control 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 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.

Voice control area

(16 Kbit Fixed)

Voice area

Phrase control table area

Depends on creation of ROM

data.

0x000000

0x0007FF

0x000800

max: 0xFFFFFF

max: 0xFFFFFF

ROM Addresses (ML2240 byte mode)