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Article #225: Exactly How Loud is Loud? Quantizing Noise

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Quantized signal differs from the actual At the receiver, pulse code modulation is
signal. It leads to introduction of same translated back into corresponding pulse
distortion called quantizing noise. We amplitude modulated pulses which are then
use word noise here since the error so demodulated using conventional methods.
introduced is random in nature. Random At the output of an idealized pulse code
nature is resulted because the difference modulation receiver we get the quantized
between the quantized level or digit and wave. The binary numbers are sent back to
actual signal at that instant of time is front to indicate each sample. Number
completely unpredictable that is random. five is sent as 1010 instead of 0101.
Evident are there that the maximum Similarly number eleven is sent as 1101
quantization error equals half the instead of 1011. In the receiver an
sampling unit. All error equals one by integrated resistance capacitance circuit
thirty two of the total signal range. We is used for conversion. The pulses are
should not assume that signal to applied to the integrating circuit and
quantizing noise ratio of this system is are then sampled and discharged
thirty two is to one because neither the immediately after the arrival of the
signal nor the instantaneous quantizing pulse. The time constant of resistance
error has always its maximum value. capacitance circuit is so chosen that the
By using statistical methods we can charge due to one pulse decays to exactly
calculate quantizing noise for a given to one half of its value by the time the
number of quantizing levels. Quantizing next pulse arrives. The each last pulse
noise reduces as the number of standard contributes to the total output in the
levels increases but increase in the preceding one micro second duration the
number of quantizing levels necessitates second last pulse will have decayed to
large number of bits to send them and half of its original value. Thus its
requires large bandwidth. In practical contribution to the output is half volt.
system for speech transmission hundred Similarly contribution of each third last
and twenty eight quantizing levels are pulse will be one by fourth volts and
sufficient. The signal is first sampled that of each fourth last will be one by
and converted to pulse amplitude eighth volts and so on. Output pulses are
modulated signal. Then the pulse obtainable only if a pulse is received in
amplitude modulated signal is quantized indicated positions.
and encoded and supervisory signals are Tymon Hytem has worked in the electronics
added. The signal is then sent directly feild for the past 15 years. He enjoys
through cable or is modulated and helping people decide on electronic
transmitted. The pulse code modulation is gadgets from telephones to XM Radio and
highly immune to noise hence amplitude choosing the perfect XM Satellite Radio
modulation may be used resulting in pulse system for their needs.
code modulation and amplitude modulation.






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