RANDOM NOISE GENERATOR

RANDOM NOISE GENERATOR

The spectrum of random noise covers all frequencies the lower density spectrum tells us how the energy of the signal is distributed in frequency, but it does not specify the signal uniquelynor does it tell us very much about how the amplitude of the signal varies with time The spectrum does not specify the signal uniquely because it contains no phase information. 

The method of generating noise is usually to use a semi conductor noise which delivers frequencies in a band roughly extending from 80 – 220 KHz The output from the noise diode is amplified and heterodyned down to audio frequency band by means of a balanced symmetrical modulator.

The filter arrangement controls the bandwidth and supplies an output signal in three spectrum choices, white noise, pink noise and Usasi noise. 


From the Fig 4.2 it is seen that white noise is flat from 20Hz to 20 KHz and has upper cutoff frequency of 50 kHz with a cutoff slope of -12

dbs/ octave. Pink noise is so called because the lower frequencies have larger amplitude, similar

to red light. Pink noise has a voltage spectrum which is inversely proportional to the square root

of frequency and is used in band analysis. 

Usasi noise ranging simulates the energy distribution of speech and music frequencies and is used for testing audio amplifiers and loud speakers.