Converting Voice Recordings

For CPU efficiency and best audio quality of prompts and music played over telephone handsets, we recommend you convert your audio source files. For example, convert .wav format to 8 bit mono 8kHz mu-law (or A-law outside of North America) format before you add the audio file to a prompt tool or Interaction Attendant application. Some audio formats can be converted automatically by the CIC system and telephony boards, but the dynamic conversion process may cause some loss of audio quality and require more CPU overhead.

To convert your audio source files:

1. Regardless of the starting format, convert it to Linear 16-bit (at the same sample rate as the starting format).

2. If the sample rate is anything other than 8 kHz, re-sample it to 8 kHz.

3. Finally, convert it from 16-bit Linear at 8 kHz to mu-Law (or A-law if you prefer).

If you are doing this manually with a sound editor, steps 1 and 3 are usually done automatically by the sound editor. For example, if you have an MP3 recording at 44.1 kHz sample rate, open it in the sound editor (which effectively converts it to 16-bit linear), re-sample the audio to 8 kHz using the sound editor, and then in the Save As… dialog convert it to mu-Law. If you using a command line utility, you might have to do all three steps individually.

The area that this most likely affects the quality of the output is the re-sampling.