A Study of the Characteristics of Noise

It is well known that when smooth noise such as hiss is passed through or generated in a radio-frequency amplifier, the root-mean-square output is proportional to the square root of the frequency band width. Experiments are described which show that the peak value of the hiss is also proportional to the square root of band width. The crest factor (defined as the ratio of the amplitudes of the highest peaks to the root-mean-square value) was found to be equal to 3.4 and independent of band width. When the noise is caused by impulse excitation with decay trains not overlapping, the result is quite different. The root-mean-square amplitude is still proportional to the square root of frequency band passed; however the peak amplitudes are directly proportional to the first power of the frequency band. This result is verified mathematically and experimentally.