TrueSpeech® Co-Processor
PRELIMINARY/CONFIDENTIAL
Version: 1.18
9.7.10
Reading the Record Level Value and Threshold Value
It is possible to read the programmed Threshold Value, together with the actual current frame average Level Value,
using the following command:
Command (CF88H or CF89H):
1100 1111 1000 1
(15-3)
00X
(2-0)
Status:
Threshold or Level Value
(15-0)
Where
X = 0
X = 1
selects reading the Level Value.
selects reading the Threshold Value.
The level value is calculated using the following algorithm:
LEVEL = 0
FOR each of 240 INPUT samples per frame
IF INPUT < 0 THEN INPUT = -1 * INPUT
LEVEL = LEVEL + INPUT
LEVEL = LEVEL/256
Note that this is an average signal level (not r.m.s.). Dividing by 256 instead of 240 leads to a slight understatement
of the true average level. The fractional error is 240/256 = 0.9375, or 6.25%. Dividing by 256 instead of 240
requires less processing by the CT8022.
When the CT8022 is operated with a base frame size that is not set to 240, the level calculation is adjusted to report
the same level as if the base frame size were set to 240. However, since the CT8022 will update and report the level
for each frame processed, with a smaller base frame size, the CT8022 will report the level measured over a shorter
period. This may result in more frame-by-frame variation in the signal level measured. When measuring the level of
a signal with lower frequency components, or with a low frequency modulation, more ripple may be observed in the
reported signal level. One example of this would be reporting the signal level of a 350+440 Hz dial tone.
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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 ]
