Native Wave Audio Formats


As with any telephony device it is important to play and record audio files (wave files) utilizing formats that are native to the device.

For example the Dialogic Proline/2V and D/4PCI supports the following formats natively:

The wave files provided with ExceleTel TeleTools are in the format “PCM 8,000 Hz, 16-bit, Mono”. If you find that they work with your Dialogic card it is because there is a CODEC (Audio COmpressor DECompressor) installed on your system that converts the file in real-time. You can see what CODECS are installed on your system by clicking on “Multimedia” in the Windows 98 Control Panel, selecting the “Devices” tab and expanding the “Audio Compression Codecs” item. You can also find other WAV file formats by checking our WEB page at www.exceletel.com/support/TelephonyHardware.htm.

Codecs.jpg

The etPlay control sends audio data to the audio device via the Windows Audio API. If the device does not support the format of the audio data, Windows will search for a CODEC that has the ability to convert the data from the current format to a supported format. Diagram 1 illustrates the data passing through a CODEC; diagram 2 does not utilize a CODEC.

CODECs are specialized drivers that receive streamed audio data in one format and output a stream of audio data in a different format. The use of a CODEC is automatic. The only way to avoid utilizing CODECs is to send the audio data to the device in a format that it supports natively.

Most CODECs seem to be work well however we have seen some create problems. For example the header information that is generated by some CODECs is not always compatible with the Dialogic audio drivers; this will cause an error.

CODECs execute at the operating system level. This is something to keep in mind if your application supports a large number of lines. For example if you had 48 lines playing wave files simultaneously requiring conversion then 48 copies of the CODEC would need to execute at the same time draining your system’s resources.

You will need to check with your telephony hardware supplier for audio formats that your device supports natively to avoid utilizing CODECs.