TrueSpeech® Co-Processor
PRELIMINARY/CONFIDENTIAL
Version: 1.18
This Mapping Table can be created using the command sequence provided after it:
Filter
F0
F1
F2
F3
Table Value
Filter Parameter Set used by Filter
7
10
9
Set 7 = 350 Hz
Set 9 = 440 Hz
Set 10 = 480 Hz
Set 11 = 620 Hz
11
Command Sequence:
5154H
5177H
5155H
517AH
5156H
5179H
5157H
517BH
Select Filter F0
Select Filter Set 7
Select Filter F1
Select Filter Set 10
Select Filter F2
Select Filter Set 9
Select Filter F3
Select Filter Set 11
9.20.8
Filter Detection Algorithm
The Filter Detection Algorithm has three stages:
1. The In-Band filter energy for each 15ms half-frame (120 samples) is compared against a minimum threshold.
By default, this is set to approximately -37 dBm0. If the energy is less than the threshold a no detect decision is
made for the half-frame.
2. The In-Band filter energy for each 15ms half-frame (120 samples) is compared against the Broad-Band energy.
If the In-Band energy is greater than 21/32 * Broad-Band energy then a detect decision is made for the half-
frame.
3. A filter detect history is constructed every frame period which covers the last 4 frames, or 8 half-frames. If a
detect decision was made in at least 5 of the last 8 half-frames, then the corresponding Filter Output Valid bit is
set in the Line Monitor Status response.
Note: dBm0 scale - For a µ-law or a-law CODEC, the full-scale input signal range of the CODEC
corresponds to approximately 3.14 dBm (0 dBm is 1 mW in 600 ohms). For signal level compatibility
across digital systems, this signal level is referred to as 3.14 dBm0. When using a 16-bit linear
CODEC, the full-scale range of this CODEC is also assumed to be 3.14 dBm0.
136
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 ]
