NSAM266SA Datasheet, PDF (43/52 Pages) National Semiconductor (TI) – NSAM266SA CompactSPEECHTM Digital Speech Processor with Serial Flash Interface

2 0 Software (Continued)
TABLE 2-2 Tunable Parameters
Index
Parameter Name
Description
0 – 3 Reserved
4
SIL THRESHOLD
Prevents speech from being interpreted as silence The silence detection
algorithm has an adaptive threshold which is changed according to the noise
level This parameter is therefore only the initial threshold level
Legal values 9216 to 13824 in 512 (6 dB) steps
5
SIL THRESHOLD STEP Defines the adaptive threshold changes step
If this threshold is too low the threshold converges too slowly If it is too high
silence detection is too sensitive to any noise
Legal values 3 to 48
6
SIL BURST THRESHOLD The minimum time period for speech detection during silence As this
threshold increases the time period interpreted as silence increases
If this threshold is too low a burst of noise is detected as speech If it is too
high words may be partially cut off
Legal values 1 to 3
7
SIL HANG THRESHOLD The minimum time period for silence detection during speech As this
threshold increases the time period interpreted as silence decreases
If this threshold is too low words may be partially cut off If it is too high
silence is detected
Legal values 8 to 31
8
SIL ENABLE
Silence compression control
0 turns silence compression off
9
ENERGY FACTOR
Determines the energy level used to synthesize silence For the default value
the energy levels of the synthesized silence and the recorded silence are the
same If you divide (multiply) the default value by two the synthesized silence
is 6 dB less (more) than the level of the recorded silence
Legal values 1024 to 16384
10 VOX ENERGY THRESHOLD This constant determines the minimum energy level at which voice is
detected Below this level it is interpreted as silence If you divide (multiply)
the value by 2 you get 3 dB decrease (increase) in the threshold
Legal values 0 to 65535
11 Reserved
12 VOX TIME COUNT
This constant in units of 10 ms determines the period of silence before the
CompactSPEECH reports silence The accuracy of the constant is g10 ms
Legal values 0 to 65535
13 – 15 Reserved
Default
11264
12
2
15
1
8192
12
700
43
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