Exactly How Loud is Loud? Quantizing Noise

Quantized signal differs from the actual signal. It leadsmodulation. At the receiver, pulse code modulation is
to introduction of same distortion called quantizingtranslated back into corresponding pulse amplitude
noise. We use word noise here since the error somodulated pulses which are then demodulated using
introduced is random in nature. Random nature isconventional methods. At the output of an idealized
resulted because the difference between thepulse code modulation receiver we get the quantized
quantized level or digit and actual signal at that instantwave. The binary numbers are sent back to front to
of time is completely unpredictable that is random.indicate each sample. Number five is sent as 1010
Evident are there that the maximum quantizationinstead of 0101. Similarly number eleven is sent as
error equals half the sampling unit. All error equals one1101 instead of 1011. In the receiver an integrated
by thirty two of the total signal range. We should notresistance capacitance circuit is used for conversion.
assume that signal to quantizing noise ratio of thisThe pulses are applied to the integrating circuit and
system is thirty two is to one because neither theare then sampled and discharged immediately after
signal nor the instantaneous quantizing error hasthe arrival of the pulse. The time constant of
always its maximum value.resistance capacitance circuit is so chosen that the
By using statistical methods we can calculatecharge due to one pulse decays to exactly to one
quantizing noise for a given number of quantizinghalf of its value by the time the next pulse arrives.
levels. Quantizing noise reduces as the number ofThe each last pulse contributes to the total output in
standard levels increases but increase in the numberthe preceding one micro second duration the second
of quantizing levels necessitates large number of bitslast pulse will have decayed to half of its original
to send them and requires large bandwidth. Invalue. Thus its contribution to the output is half volt.
practical system for speech transmission hundred andSimilarly contribution of each third last pulse will be
twenty eight quantizing levels are sufficient. Theone by fourth volts and that of each fourth last will
signal is first sampled and converted to pulsebe one by eighth volts and so on. Output pulses are
amplitude modulated signal. Then the pulse amplitudeobtainable only if a pulse is received in indicated
modulated signal is quantized and encoded andpositions.
supervisory signals are added. The signal is then sentTymon Hytem has worked in the electronics feild for
directly through cable or is modulated andthe past 15 years. He enjoys helping people decide on
transmitted. The pulse code modulation is highlyelectronic gadgets from telephones to XM Radio and
immune to noise hence amplitude modulation may bechoosing the perfect XM Satellite Radio system for
used resulting in pulse code modulation and amplitudetheir needs.