September 2008
Intermediate to advanced
550 pages
18h 10m
English
Content preview from VoIP Voice and Fax Signal ProcessingBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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VoIP VOICE FAQS
- What are the important voice band frequencies?
Narrowband speech is important between 300 and 3400 Hz. The bandwidth is 3100 Hz. It is also referred to as 3k (or 3K) flat band, which means 3000-Hz bandwidth. Wideband is gaining popularity through VoIP and multimedia terminals. Wideband voice frequencies are from 100 to 7000 Hz. Sometimes wideband is also referred to in the range 50 to 7000 Hz.
- What are dBm and other related dB units?
The ratio of two quantities in logarithmic scale is represented in deciBel (dB) units. In power representation, when the reference power is 1 milliWatt, the dB units are denoted as dBm, where “m” represents 1 milliWatt of power. Speech power levels are expressed in dBm units. Noise power is low and expressed using picoWatt units represented as dBrn; 0 dBm = 90 dBrn (rn is referenced for noise power of 1 picoWatt).
- What are the speech signal levels?
The undistorted sine wave amplitude in μ-law is 3.17 dBm, which gives quantized sample values in the range of ±8159. The full-scale square wave gives 6.17 dBm. In A-law, sine wave power is 3.14 dBm, and samples are in the range of ±4096. Typical speech levels are at −16 dBm, and ideal channel noise is lower than −68 dBm (22 dBrn). When speech levels are approaching −40 dBm, speech is not perceivable clearly.
- What are 3K flat, dBrn, dBrnC, dBp, dBmp and pWp?
Signals are measured with milli-Watt (mW) reference and noise is measured with pico-Watt reference (pW). The noise measurement without ...
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