Version: 1.18
PRELIMINARY/CONFIDENTIAL
TrueSpeech® Co-Processor
9.8.5
Select TrueSpeech Playback Rate
This command allows the Host to select the TrueSpeech data rate used in compressed playback mode. The standard
built-in available rates are: TrueSpeech 6.3, 5.3, 4.8 and 4.1 KBPS. This command should be issued prior to starting
playback using the Playback command. The TrueSpeech Playback Rate remains in effect until the next TrueSpeech
Playback Rate command.
Command (523XH):
0101
0010
0011
(7-4)
RATE
(3-0)
(15-12)
(11-8)
Status (523XH):
0101
0010
0011
(7-4)
RATE
(3-0)
(15-12)
(11-8)
RATE
TrueSpeech Compression Rate
Compressed Frame Size (16-bit words)
0
1
2
16
12
10
9
8.5 (see Note)
6.3 (G.723.1) (default)
5.3 (G.723.1)
4.8
3
4
4.1
8
5
Reserved
6
6 (10ms)
G.729AB (see Note)
G.722 (see Note)
Reserved
7
40 (10ms)
8-15
The Frame Size value indicates the number of 16-bit words in a compressed speech frame for each coding rate.
When any of the TrueSpeech compression rates are selected, the frame size is always 16 words or less. Since the
size of the CT8022 hardware buffer within the Host port is 16 words, the Host can burst write the complete speech
frame of 16-8 words without checking the RX Ready bit before each individual word is read. Where the frame size
is larger than 16 words, the CT8022 splits the data transfer into sub-blocks of 16 words or less.
Note: The CT8022 supports the G.729AB and G.722 coders only as external downloadable software
expansion modules. The Host must ensure that the appropriate module is loaded to the CT8022
external program/data memory before attempting to activate any of these coders. Contact DSP
Group for information.
The two least significant bits of the first data word of a G.723.1 6.3 or 5.3 speech frame are encoded to indicate the
speech frame type.
During Playback (de-compression) the CT8022 will test the two least significant control bits only when the current
Host-selected TrueSpeech rate is 6.3 or 5.3. In this case, the CT8022 will automatically perform the correct
decoding of the speech frames independently of which rate is selected by the Host. This includes automatic
decoding of the G.723.1 CNG (Comfort Noise Generation or silence) frames.
To support on-the-fly switching for Playback, Playback must be started with the 6.3 rate selected. This fixes the
frame size used for Host-to-CT8022 transfer at 12 words. When transferring a 5.3 speech frame to the CT8022
when the 6.3 rate was initially selected, the Host should append two dummy words (zeros) at the end of the 10 word
TrueSpeech 5.3 frame.
Refer to Section 9.7.7 regarding on-the-fly switching between TrueSpeech 6.3 and 5.3 data rates.
CT8022A11AQC FW Revision 0118 DSP GROUP, INC., 3120 SCOTT BOULEVARD
SANTA CLARA, CA 95054 PH: 408 986 – 4300 FAX: 408 986 – 4490
81
All specifications are subject to change without prior notice.
ETC [ ETC ]
