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from the Plum Voice IVR Glossary
A-law is a lossy method of audio encoding that will compress 16-bit linear PCM audio samples into 8-bit samples thereby reducing bitrate by 50%. Like its encoding cousin, u-law, a-law assumes that the audio stream contains predominantly voice data which has a high dynamic range (as opposed to, say, music data). It then uses a pseudo-logarithmic algorithm to compress the data, favoring detail for samples in the “middle” of the range and effectively glossing over samples at the extremes.
A-law is used to encode voice data on telecom networks outside of North America. Thus, the Plum IVR infrastructure in London uses a-law. Conversely, the Plum Voice IVR infrastructure in the US uses u-law on all of its telecom circuits. However, the audio files referenced within VoiceXML code written for the Plum IVR platform can be encoded as monophonic 8khz u-law, a-law, or linear 16-bit PCM and either encapsulated in a .wav file or sent as a raw, headerless data stream as long as the correct MIME-type is sent by your web server (audio/basic, audio/x-alaw-basic, or audio/l16 respectively).
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