Voice API Programming Guide — June 2005 95
Recording and Playback
•G.711 PCM, 6 kHz with 8-bit samples (48 kbps) and 8 kHz with 8-bit samples (64 kbps) using
A-law or mu-law coding, VOX and WAVE file formats
•G.721 at 8 kHz with 4-bit samples (32 kbps), VOX and WAVE file formats
•G.726 bit-exact voice coder at 8 kHz with 2-, 3-, 4-, or 5-bit samples (16, 24, 32, 40 kbps),
VOX and WAVE file formats
On Springware boards, the following encoding algorithms and sampling rates are supported in
SCR:
•6 kHz and 8 kHz OKI ADPCM
•8 kHz and 11 kHz linear PCM
•8 kHz and 11 kHz A-law PCM
•8 kHz and 11 kHz mu-law PCM
8.9 Recording with the Voice Activity Detector
Recording with the voice activity detector is discussed in the following topics:
•Overview
•Enabling
•Encoding Methods Supported

8.9.1 Overview

The dx_reciottdata( ) function, used to record voice data, has two modes that work with the voice
activity detector. One mode enables voice activity detection with event notification upon detection.
The second mode adds initial silence compression on the line before voice energy is detected; if
initial silence is greater than the default allowable amount of silence, the amount in excess is
eliminated. This mode uses the same algorithm as the silence compressed record (SCR) feature
described in Section 8.8, “Silence Compressed Record”, on page 93.
The voice activity detector (VAD) is a component in the voice software that examines the incoming
signal and determines if the signal contains significant energy and is likely to be voice.
The recording modes for voice activity detection are supported on select DM3 boards only and
with certain encoding methods only. For more information about boards supported and the features
supported on each board, see the Release Guide for your system release. For more information
about encoding methods supported, see Section 8.8.3, “Encoding Methods Supported”, on page 94.