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What is the Mu-Law PCM voice coding standard used in North American T-Carrier telecommunications transmission systems? June 8, 2009

Posted by HubTechInsider in Definitions, Telecommunications, VUI Voice User Interface.
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Sampling and 4-bit quantization of an analog s...

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Mu-Law encoding is the PCM voice coding standard used in Japan and North America. It is a companding standard, both compressing the input and expanding the data upon opening after transmission. Mu Law is a PCM (Pulse Code Modulation) encoding algorithm where the analog voice signal is sampled eight thousand times per second, with each sample being represented by eight bits, thus yielding a raw transmission rate of 64 Kps. Each sample consists of a sign bit, a three bit segment which specifies a logarithmic rqange, and a four bit step offset into the range. The bits of the sample are inverted before transmission. A Law encoding is the voice coding standard which is used in Europe.

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What is the frequency response of the North American Public Switched Telephone Network? June 3, 2009

Posted by HubTechInsider in Telecommunications, VoIP, VUI Voice User Interface, Wireless Applications.
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Sinusoidal waves of various frequencies; the b...

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The conventional North American Public Switched Telephone Network, or PSTN, has a frequency response range of 300 Hz to 3,400 Hz. The normal hearing range of humans is typically 30 Hz to 20,000 Hz. So the conventional telephone transmission system is unable to carry bright, high-frequency and deep, low-frequency tones.

But, somewhat surprisingly, because our ears are so used to hearing poor-quality audio over the telephone, our brains actually “fill in” the missing frequencies. As an example, the crisp “s” sound in the word “Christmas”. So in effect, the telephone audio often sounds better than it actually is to us.

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