Audio Downsampler

Although the Tellme VoiceXML interpreter supports downsampling of high fidelity formats on the fly, it is more efficent to convert your audio files into a format that is optimal for use on the public switched telephone network (PSTN). You can use Tellme's audio conversion tool to downsample your master audio files (usually 44.1kHz) into the optimal format. The optimal format is the following:

1. Supported source formats

The conversion tool supports RIFF wav (any sample rate) and Sphere wav (any sample rate) as input. The tool does not support MP3 or RealAudio formats.

2. System Requirements

To use the converter (convert.pl), you need the following:

3. Installing the converter

Microsoft Windows users should follow these steps to use the audio converter:

4. Using the converter

Follow these steps to use the converter to downsample a set of audio files:

  1. Copy the audio files you wish to downsample into your input directory.
  2. Open a command shell (MS-DOS prompt) and run the converter using a command in the following format:
    perl convert.pl input-dir  output-dir

Your converted audio files will be found in your output directory.

5. Additional Features

The conversion tool provides the ability to adjust the peak amplitude and the rms amplitude. These features are describe in the following sections.

5.1. Adjusting peak amplitude

To change the volume of the sound, use the following command:

perl convert.pl indir  outdir peak value

The value argument is a number between 0.0 and 1.0.

5.2. Adjusting the rms amplitude

If your audio produces lots of clicks and pops, increasing the volume might help. Use the following command:

perl convert.pl indir outdir rms value

The value argument is a number between 0.0 and 1.0. This argument could reduce sound quality. Be sure to listen to the resulting output files.

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