Teleconference systems permit a group of people in one room to both speak to and
ID: 3162970 • Letter: T
Question
Teleconference systems permit a group of people in one room to both speak to and see a group of people in another room. For simplicity, it is desirable to use only one microphone in each room. However, we are then faced with a problem of directivity. If the microphone is omnidirectional, then in addition to speech it also picks up considerable reverberation due to reflections and background noise. A certain microphone under development may be modeled as a vertical line source that is 0.7 m in length. The microphone is placed in the middle of the table so that its center is at the average height of people's heads. Discuss the merits of this arrangement, in terms of half-power beam width 2 theta_HP with respect to the nominal telephone bandwidth for speech (300-3300 Hz).Explanation / Answer
Teleconferencing means meeting through a telecommunications medium. It is a generic term for linking people between two or more locations by electronics. There are at least six types of teleconferencing: audio, audiographic, computer, video, business television (BTV) and distance education.
The methods used differ in the technology, but common factors contribute to shared definition of teleconferencing :
The "half-power beamwidth" is a measure of the directivity of the antenna. The "bandwidth" is a measure of how much the frequency can be varied while still obtaining an acceptable VSWR (2:1 or less) and minimizing losses in unwanted directions.
The example of telephone grade speech signal having a narrow bandwidth of 3.1 kHz (from 300 Hz to 3.4 kHz) will be used extensively in this module.
The bandwidth of an audible signal (voice, music etc.) is less than 20 kHz (typical frequency range is between 20 Hz and 20KHz). Interestingly, the typical bandwidth of about 20 kHz is not considered for designing a telephone communication system. Most of the voice signal energy is limited within 3.4 KHz.
While a small amount of energy beyond 3.4 KHz adds to the quality of voice. The two important features are as :
(a) message intelligibility (b) speaker recognition
which are retained when a voice signal is band limited to 3.4 kHz. This band limited voice signal is commonly referred as ‘telephone grade speech signal’.
A standard rate of sampling for telephone grade speech signal of one speaker is 8-Kilo samples/ sec (Ksps).
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