isd-t360sb ETC-unknow, isd-t360sb Datasheet - Page 46

• Manufacturer Part Number: isd-t360sb
• Manufacturer: ETC-unknow

ISD-T360SB
2.3.1
The VoiceDSP processor implements a state of the
art VCD algorithm of the CELP family. The algo-
rithm provides 3 compression rates that can be
selected dynamically. PCM recording (no com-
pression) is also provided.
The lowest compression rate of 4.7 Kbit/s enables
about 30 minutes of recording on an 8-Mbit de-
vice. The mid compression rate of 6.7 Kbit/s pro-
vides about 20 minutes of voice recording time.
The highest compression rate of 8.7 Kbit/s, which
provides the best compressed voice quality,
stores approximately 10 minutes on an 8-Mbit de-
vice. For detailed information about recording
times refer to Table 1-5.
Before recording each message, the microcon-
troller selects one of the three compression rates,
or PCM recording, with the compression_rate pa-
rameter of the R (Record) command. During mes-
sage playback the VoiceDSP processor reads this
one byte parameter and selects the appropriate
speech decompression algorithm.
IVS vocabularies can be prepared in either of the
three compression rates, or in PCM format, using
the IVS tool. All messages in a single vocabulary
must be recorded using the same algorithm. (See
the IVS User’s Guide for more details). During
speech synthesis, the VoiceDSP processor auto-
matically selects the appropriate speech decom-
pression algorithm.
VARIABLE SPEED PLAYBACK
This feature increases or decreases the speed of
messages and synthesized messages during
playback. Use the SPS (Set Playback Speed) to set
the speed of message playback. The new speed
applies to all recorded messages and synthesized
messages (only if synthesized using IVS), until
changed by another SPS command. If this com-
mand is issued while the VoiceDSP processor is in
the PLAY state, the speed also changes for the
message currently being played.
The speedup / slowdown algorithm is designed to
maintain the pitch of the original speech. This ap-
2-10
VCD (VOICE COMPRESSION AND
DECOMPRESSION)
proach provides the same speech tone while
playback speed varies.
CONVERSATION RECORDING / PLAYBACK
The VoiceDSP supports the conversation recording
feature, which enables the user to simultaneously
record the far end caller and near end caller. The
VoiceDSP simultaneously records data from chan-
nels 0 and 1 by summing the two channels and
then compressing the summation. The data is
then saved in the flash memory. When Playing the
compressed message, the data is simultaneously
broadcast to both channels. This feature is avail-
able for all compression rates. This feature can be
operated using the SLC command. For more de-
tails, refer to the SLC command in the Command
Description section.
PCM RECORDING
The VoiceDSP is capable of recording data in
PCM format (that is the original samples format ei-
ther in 8 bit u-Law format, 8 bit A-law format or 16
bit linear format). The PCM data uses more stor-
age space, but it provides the highest quality for
OGM, music-on-hold or IVS data. The PCM record-
ing may be selected as one of the available
compression rates during the R command
(compression_rate = 0).
Variable Speed Playback is not accessible during
PCM recording and playback.
Voice Solutions in Silicon
2—SOFTWARE
™