TrueSpeech® Co-Processor
PRELIMINARY/CONFIDENTIAL
Version: 1.18
9.10.2
Set Record/Playback Volume Control
Command (C1): CF02H/CF03H
1100 1111
(15-8)
0000 00
(7-2)
1
INPUT
(0)
(1)
Status (S1):
1100 1111
(15-8)
0000 00
(7-2)
1
INPUT
(0)
(1)
INPUT:
Set to 0, writes playback (output) volume
Set to 1, writes record (input) volume
Command (C2):
RECORD/PLAYBACK VOLUME
(15-0)
Status (S2):
RECORD/PLAYBACK VOLUME
(15-0)
The Record/Playback volume is a “Q8” number that is used to scale the input (record) signal or output (playback)
signal.
The scaling performed is input or output signal multiplied by (RECORD or PLAYBACK VOLUME)/100H.
So that a record/playback volume setting of:
100H scales the signal by 1.0
200H scales the signal by 2.0
80H scales the signal by 0.5
There is no protection against over-scaling. If the multiplication factor x the input signal exceeds 16 bits, overflow
(distortion) will occur.
With an external G.711 A-law or µ-law CODEC, the CT8022 provides bit-transparent data transfer between the
CODEC and the Host when operated in A-law/µ-law record/playback mode with a volume setting of 1.0 (0100H).
For best audio performance, external hardware should perform optimal scaling of the record signal before A-to-D
conversion by the CODEC, such that the full dynamic range of the CODEC is utilized. Failure to use appropriate
external gain will introduce increased quantization noise b into the recording. Note however, that excessive external
gain may cause problems with correct operation of the Acoustic Echo Canceller. Further, if the AEC feature is used,
the external gains must be fixed.
Note: Do not attempt to use the CT8022 AEC feature with an external hardware AGC or ALC circuit.
86
DSP GROUP, INC., 3120 SCOTT BOULEVARD CT8022A11AQC FW Revision 0118
SANTA CLARA, CA 95054 PH: 408 986 – 4300 FAX: 408 986 – 4490
All specifications are subject to change without prior notice.
ETC [ ETC ]
