94 Voice API Programming Guide — June 2005
Recording and Playback
with SCR. For more information on modifying SCR parameters, see the Configuration Guide for
your product or product family.
On Springware boards, you enable SCR in the voice.prm file which is downloaded to the board
during initialization. You must edit this file and set appropriate values for the SCR parameters for
use in your working environment before initializing the board. You cannot enable this feature
through the voice API. After SCR is enabled in the voice.prm file, it is automatically activated by
the use of voice record functions such as dx_rec( ).
On Springware boards, the SCR parameters specify the silence threshold, the duration of silence at
the end of speech before silence compression begins, the duration of a glitch in the line which does
not stop silence compression, and more. Figure 14 illustrates how these parameters work. See the
appropriate Configuration Guide for details of the parameters and information on how to enable
and configure this feature.
Figure 14. Silence Compressed Record Parameters Illustrated
8.8.3 Encoding Methods Supported
On DM3 boards, the following encoding algorithms and sampling rates are supported in silence
compressed record (SCR):
•OKI ADPCM, 6 kHz with 4-bit samples (24 kbps) and 8 kHz with 4-bit samples (32 kbps),
VOX and WAVE file formats
•linear PCM, 8 kHz sampling 64 Kbps (8 bits), 8 kHz sampling 128 Kbps (16 bits), VOX and
WAVE file formats
SCR_THRES
(dB)
Begin
Compression
Begin
Compression
Speech
Detected
Compression
Ends Silence Less
Than SCR_T
Compression
Not Enabled
Noise Spike
(Glitch)
Compression
Continues
SCR_T
(10 ms Unit)
SCR_PC
(Bytes)
SCR_T
(10 ms Unit)
SCR_DG
(10 ms Unit)
End of
Speech
SCR_PC
(bytes)