|MadSci Network: Physics|
Brian, There is much misunderstanding regarding white noise. Only one thing qualifies as white noise, and that is described by britannica.com. Britannica states white noise is: "the effect of the complete range of audible sound-wave frequencies heard simultaneously, analogous to white light which contains all the frequencies of the light spectrum... White noise is aperiodic sound (that is, its wave pattern is not uniform). It's constituent frequencies are of random amplitude and occur at random intervals." They explain it pretty well so please forgive my cut and paste here. See the actual reference at: http://www.britannica.com/bcom/eb/article/3/0,5716,78873+1+76834,00.html? query=white%20noise Britannica.com is an exceptional source of technical information which mirrors and in some cases exceeds what I have been taught in the classroom on many subjects - I strongly recommend it as a reference. (I have been surprised by how good!) While I can't vouch for the following company, I can ascertain that the reference information they give is good on white and pink noise as they apply to sound masking (they don't apply) and their description of the uses of white and pink noise are very good. (I am not really familiar with "fixed percentage bandwidth filters" so I can neither confirm nor deny that particular info however...) http://www.ivie.com/pages/white_vs_masking_noise.html So regarding your question, city noise may approach white noise under random circumstances but would require considerable analysis to verify and then would only qualify probably for seconds or milliseconds at a time. (Actually I am only surmising this - the best way to know how close of an approximation city noise is would be to run a sound level - time - frequency analysis and see the actual nature of the noise. My experience in cities would suggest that while the "background noise" could approximate this very thing, the intensity of certain frequencies from time to time such as honking horns, whistles, and buses accelerating etc would minimize the amount of time the approximation would be good.) The best place to find white noise would be to generate it in a lab. By its very definition, only white noise as described above would qualify as white noise (britannica describes a couple of musical instruments that demonstrate some white noise characteristics, but white noise is white noise.) I hope this helped. Sincerely, Steven Miller firstname.lastname@example.org Undergrad - Mechanical Engineering San Diego State University
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