• 5.14.1. DX_XPB Overview
• 5.14.2. DX_XPB Definition
• 5.14.3. DX_XPB Parameters
• G.726 Voice Coder Support
• GSM Voice Coder Support

5.14. DX_XPB: Input/Output Transfer Parameter Block

The DX_XPB data structure contains parameters for the Input/Output Transfer Parameter Block.

5.14.1. DX_XPB Overview

Use the I/O Transfer Parameter Block (DX_XPB) data structure to specify the file format, data format, sampling rate, and resolution for the extended play and record functions, dx_playvox( ), dx_recvox( ), dx_playiottdata( ), dx_reciottdata( ), and dx_recwav( ).

The dx_playwav( ) convenience function does not specify a DX_XPB structure because the WAVE file header contains the necessary format information.

The G.726 and GSM voice coders are supported by the I/O functions that use a DX_XPB data structure:

• The G.726 voice coder is supported by the dx_playiottdata( ), dx_reciottdata( ), dx_playvox( ), and dx_recvox( ) functions.
• The GSM voice coders are supported by the dx_playiottdata( ), dx_reciottdata( ), and dx_recwav( ) functions.

When you play a voice file recorded in GSM or G.726, you must specify the format (this is necessary even for the GSM WAVE files, although you can normally play WAVE files without specifying the format because it is stored in the header).

5.14.2. DX_XPB Definition

The typedef for the structure is as follows:

      typedef struct {

            USHORT      wFileFormat;         // file format

            USHORT      wDataFormat;         // audio data format

            ULONG       nSamplesPerSec;      // sampling rate

            ULONG       wBitsPerSample;      // bits per sample

      } DX_XPB;




5.14.3. DX_XPB Parameters

Parameter	Description
wFileFormat	Specifies one of the following audio file formats. Note that this field is ignored by the convenience functions dx_recwav( ), dx_recvox( ), and dx_playvox( ).
	FILE_FORMAT_VOX	Dialogic VOX file format
	FILE_FORMAT_WAVE	Microsoft WAVE file format
wDataFormat	Specifies one of the following data formats:
	DATA_FORMAT_DIALOGIC_ADPCM	4-bit OKI ADPCM (Dialogic registered)
	DATA_FORMAT_MULAW	8-bit mu-law PCM
	DATA_FORMAT_ALAW	8-bit a-law PCM
	DATA_FORMAT_PCM	8-bit Linear PCM
	DATA_FORMAT_G726	G.726 bit-exact coder
	DATA_FORMAT_GSM610_ MICROSOFT	GSM 6.10 WAVE full-rate coder (Microsoft Windows compatible format)*
	DATA_FORMAT_GSM610_ TIPHON	GSM 6.10 WAVE full-rate coder (TIPHON format)**
nSamplesPerSec	Specifies one of the following sampling rates:
	DRT_6KHZ	6 KHz sampling rate.
	DRT_8KHZ	8 KHz sampling rate.
	DRT_11KHZ	11 KHz sampling rate. Note: 11KHz OKI ADPCM is not supported.
wBitsPerSample	Specifies the number of bits per sample. This field must be set to 8 for MULAW, ALAW, and PCM. Set the field to 4 for ADPCM. For G.726 and GSM, refer to the following information.

*Microsoft Windows Media Recorder Audio Compression Codec: GSM 6.10 Audio CODEC

**See ETSI (European Telecommications Standards Institute) Technical Specification TS 101 318: Telecommunications and Internet Protocol Harmonization Over Networks; Using GSM speech codecs within ITU-T Recommendation H.323

G.726 Voice Coder Support

The G.726 voice coder is supported through the following parameters:

wFileFormat	FILE_FORMAT_VOX
wDataFormat	DATA_FORMAT_G726
nSamplesPerSec	DRT_8KHZ
wBitsPerSample	4	(Note: 32 Kb/s.)

GSM Voice Coder Support

The GSM voice coder is supported through the following parameters:

wFileFormat	FILE_FORMAT_WAVE
wDataFormat	DATA_FORMAT_GSM610_MICROSOFT
	DATA_FORMAT_GSM610_TIPHON
nSamplesPerSec	DRT_8KHZ
wBitsPerSample	0 (can be any numeric value; ignored; recommended setting is 0)	(Note: 13 Kb/s.)

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