NSAM266SAASLASHV datasheet(25/52 Pages) NSC

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20 Software (Continued)

A message is the basic unit on which most of the Compact-

SPEECH commands operate A CompactSPEECH mes-

sage stored on a flash device can be regarded as a com-

puter file stored on a mass-storage device

A message is created with either the R or the WRAM (Write

Memory) command

When a message is created it is assigned a time-and-day

stamp and a message tag which can be read by the micro-

controller

The R command takes voice samples from the codec com-

presses them and stores them in the message memory

When a message is created with the WRAM command the

data to be recorded is provided by the microcontroller and

not via the codec The data is transferred directly to the

message memory It is not compressed by the Compact-

SPEECH voice compression algorithm

The WRAM command together with the RRAM (Read

Memory) command which enables the microcontroller to

read data from the CompactSPEECH can be used to store

data other than compressed voice in the message memory

eg a telephone directory

A message can be played back (P command) and deleted

(DM command) Redundant data (eg trailing tones or si-

lence) can be removed from the message tail with the CMT

(Cut Message Tail) command

The PA (Pause) and RES (Resume) commands respective-

ly temporarily suspend the P and R commands and then

allow them to resume execution from where they were sus-

pended

CURRENT MESSAGE

Most message handling commands eg P DM RRAM op-

erate on the current message The GTM (Get Tagged Mes-

sage) command selects the current message

Deleting the current message does not cause a different

message to become current The current message is unde-

fined If however you issue the GTM command to skip to

the next message the first message that is newer than the

just deleted message is selected as the current message

261 Message Tag

Each message has a 2-byte message tag which you can

use to categorize messages and implement such features

as OutGoing Messages mailboxes and different handling

of old and new messages

The most significant bit (bit 15) of the message tag is used

to indicate the speech compression rate The microcontrol-

ler should program it before recording (‘‘1’’ for 48 kbits

‘‘0’’ for 66 kbits) The CompactSPEECH reads the bit be-

fore message playback to select the appropriate decom-

pression algorithm

The GMT (Get Message Tag) and SMT commands may be

used to handle message tags

Note

Message tag bits can only be cleared Message tag bits are set only

when a message is first created

This limitation is inherent in flash memories which only allow bits to

be changed from 1 to 0 (changing bits from 0 to 1 requires a special

erasure procedure see Section 135) However the main reason for

updating an existing tag is to mark a message as old and this can be

done by using one of the bits as a newold indicator setting it to 1

when a message is first created and clearing it when necessary

27 SPEECH COMPRESSION

The CompactSPEECH implements two speech compres-

sion algorithms One algorithm with 52 kbits compression

rate enables up to 14 – 16 minutes of recording on a 4-Mbit

device while the other uses a 73 kbits compression rate

to support 10 – 12 minutes of recording Both compression

rates assume 10% silence

Before recording each message the microcontroller can se-

lect one of the two algorithms by programming bit 15 of the

message tag

During message playback the Compact-

SPEECH reads this bit and selects the appropriate speech

decompression algorithm

IVS vocabularies can be prepared in either of the two com-

pression formats using the IVS tool All the messages in a

single vocabulary must be recorded using the same algo-

rithm (See the

IVS User’s Manual for further details) During

speech synthesis the CompactSPEECH automatically se-

lects the appropriate speech decompression algorithm

28 TONE AND NO-ENERGY DETECTION

The CompactSPEECH detects DTMF busy and dial tones

and no-energy (VOX) This enables remote control opera-

tions and call progress Detection is active throughout the

operation of the CompactSPEECH Detection can be con-

figured using the SDET (Set Detectors Mask) command

which controls the reporting of the occurrence of tones and

the RDET (Reset Detectors) command which resets the de-

tectors

DTMF

DTMF detection may be reported at the starting point end-

ing point or both The report is made through the status

word (for further details see GSW command in Section

214)

The DTMF detector performance as measured on the line

input using an NSV-AM265-DAA board is summarized be-

low (see Table 2-1)

ECHO CANCELLATION

Echo cancellation is a technique used to improve the per-

formance of DTMF tone detection during speech synthesis

tone generation and OGM playback For echo cancellation

to work properly AGC must not be active in parallel Thus

to take advantage of echo cancellation the microcontroller

must control the AGC ie disable the AGC during PLAY

SYNTHESIS

and TONE

GENERATE

states and enable it

again afterwards If AGC cannot be disabled do not use

echo cancellation The microcontroller should use the CFG

command to activatedeactivate echo cancellation (For fur-

ther details see Section 214)

Echo cancellation applies only to DTMF tones Busy and

dial-tone detection is not affected by this technique This

implies that the performance of the busy and dial-tone de-

tector during message playback depends on the message

being played

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