(c) Copyright 1996 Bob Edgar, all rights reserved.

The table summarizes the different telephony sound file formats and the drivers which support them.

Voice File Support

File Type Supported by Dialogic API1 Supported by Dialogic TSP Supported by desktop WAVE cards Data Rate

4-bit, 6 kHz ADPCM VOX Yes No No 24 kbps

4-bit, 8 kHz ADPCM VOX Yes No No 32 kbps

8-bit, 6 kHz mu-law PCM VOX Yes No No 48 kbps

8-bit, 6 kHz A-law PCM VOX Yes No No 48 kbps

8-bit, 8 kHz mu-law PCM VOX Yes No No 64 kbps

8-bit, 8 kHz A-law PCM VOX Yes No No 64 kbps

4-bit, 6 kHz Dialogic ADPCM WAVE Yes Yes No 24 kbps

4-bit, 8 kHz Dialogic ADPCM WAVE Yes Yes No 32 kbps

8-bit, 6 kHz mu-law PCM WAVE Yes Yes No 48 kbps

8-bit, 6 kHz A-law PCM WAVE Yes No No 48 kbps

8-bit, 8 kHz mu-law PCM WAVE Yes Yes No 64 kbps

8-bit, 8 kHz A-law PCM WAVE Yes No No 64 kbps

8-bit, 6 kHz linear PCM WAVE Yes Yes Some, not all 48 kbps

8-bit, 8 kHz linear PCM WAVE Yes Yes Some, not all 64 kbps

8-bit, 11 kHz linear PCM WAVE Yes Yes Yes 88 kbps

8-bit, 22 kHz linear PCM WAVE No No Yes 176 kbps

8-bit, 44 kHz linear PCM WAVE No No Yes 352 kbps

[1] Not all formats marked "Yes" supported on all boards.

So when you hear "Dialogic supports WAVE", remember that things are not as simple as they might appear (might sound?). Out of the 11 WAVE formats in the table, there is only one (11 kHz linear) that is supported by the Dialogic API, the Dialogic TSP and all Windows sound cards.

Applications for TAPI/WAVE have a special problem when it comes to this proliferation of sound file types. The WAVE API does not allow an application to ask for a list of encoding formats which a device supports. The waveInGetDevCaps and waveOutGetDevCaps functions return only a bitmap which specifies which of the 12 standard WAVE formats are supported by the device. It is possible to ask if a given format is supported, by using waveIn/OutOpen with the WAVE_FORMAT_QUERY parameter, but this means that the application must know about proprietary formats, such as the Dialogic WAVE files with VOX encoding, in advance. Of course, this undermines the hardware-independence of the API: it is always an important feature of an API, especially one which aims for hardware independence, that the application be able to determine the installed hardware and its capabilities.

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