You’ve got this great MP3 of your young child doing all the names for your brand-spankin’ new auto-attendant that you’ve created using Tropo, and when you go to call the application, it now sounds like some space alien has taken over your program! Dude, what happened?!?

Well, as it turns out, while cellphones and MP3 players can play audio files like stereo MP3s, they must be “local” on your device. See, telephony standards have just not “kept up with the times.” In Telephony the standard is 8bit, 8Khz u-law formatted WAV, and that standard, is generations removed from that nice 44KHz, 32-bit, stereo MP3 you just recorded. So, in order to play your MP3, it must be converted, on-the-fly, to work on the proper telephony standard — and unfortunately, that usually leads to less than stellar results.

The Tropo platform supports a number of different audio formats. When converting your sound files for optimum performance in your application, it is always best to have your files in 8bit, 8Khz u-law format from the start.

The supported sound formats (and their proper file extensions) for the Tropo platform are as follows:

• 8kHz, 8bit u-law (wav or raw) (*.wav or *.ulaw)
• 8kHz, 8bit a-law (wav or raw) (*.wav or *.alaw)
• 8kHz, 8bit pcm (wav) (*.wav)
• 8khz, 16bit pcm (wav or raw) (*.wav or *.pcm)
• MS-GSM (wav) (*.wav)
• GSM 6.10 (raw) (*.gsm)

Recording your own prompts

• If you don’t plan on mixing and editing the prompts they record, it’s best to just record at 8khz/16bit and then save or convert to 8khz/8bit-ulaw.
• If you plan on mixing and editing prompts you have recorded, it’s best to record at 48Khz/16bit, and not 44Khz, (the down-sample to 8Khz works much better when you are dealing with something that is a multiple of 8k), and then save or convert to 8khz/8bit-ulaw when you are done mixing and editing their prompts.
• Most definitely use the gain control tools in your audio software to adjust the RMS amplitude and peak amplitude of your audio recordings so that audio is loud enough to be heard by customers; but not so loud that prompt echoes will be heard by the recognition engine; and not so loud that pops and clicks are heard as a result of clipping.

Tools

A great, free, cross-platform tool for working with audio files is Audacity. Their wiki and Forums offer outstanding support for folks using their application for the first time.

Another cross-platform, open-source audio editor application is SoX. SoX is a command-line utility, but has some outstanding capabilities for processing those “hard to fix” audio files.

For those PC-only folks out there, Goldwave is another freeware audio editor that you may want to consider, if Audacity or SoX does not fit the bill for you.

We hope that these hints help you in preparing your audio files for successful use on Tropo.