For example, ambient noise is reference sound level or average room noise level.  To measure the ambient noise, get a device to measure SPL-sound pressure level and measure noise/sounds often.  SPL measures are taken with respect to the minimum threshold for human hearing.  A 20 dB difference in SPL represents a ratio of ten-to-one in sound pressure.  For example, 40dB SPL would be a SPL-sound pressure level that is 100 times greater than the sound pressure level of the quietest sound that normal human hearing can detect.  If you would like to test your own hearing go here: http://www.freehearingtest.com/test.shtml

170 dB = rifle fire at 1m

160 dB = personal protection air horn

150 dB = rock music

140 dB = firearms (which go even higher), jet engine

130 dB = jackhammer

120 dB = car stereo, band practice, threshold of pain

110 dB = manufacturing machines, rock music

100 dB = chain saw, drills, car horns, motorcycle

90   dB = lawnmower, shop tools, truck traffic, city subway, construction machinery

80   dB = inside sports car at high speed, outside busy street, alarm clock, telephone dial tone

70   dB = vacuum cleaner,

60   dB = human speech, conversation

50   dB = open office background level, dishwasher in next room

40   dB = maximum recommended background room noise level for tele/presence room

30   dB = soft whisper

20   dB = quiet interior house

10   dB = normal human breathing

0     dB = silence

SN or SNR-Signal-to-Noise or CNR-Carrier-to-Noise ratio is the difference between the signal also known as carrier or carrier wave and noise.  The SPL of human voice is 60dB to 70dB.  If you get an SPL meter you can test various sound conditions such as watching television, working, coffee shops, etc.  In practical terms, according to Cisco's TelePresence Fundamentals book (ISBN-1-58705-593-7), "Because of the way the human ear and brain work, background sound that is 25dB to 30dB less than human speech generally goes unnoticed. In other words, the carrier/signal should be 60-70 dB and the background should be less than approximately 35dB. Noise levels exceeding 42dB are cause for concern, and levels exceeding 50dB can cause significant problems with the tele/presence experience."

 

According to Cisco's TelePresence Fundamentals book, "Within each of the six zones, the ambient noise is measured with the decibel meter approximately 5 feet from the floor using a slow sweeping motion to capture the average SPL for that zone. These measurements are done using an A-weighted test (best SPL analysis for human ears). A seventh measurement is taken using a C-weighted (best SPL for all uses including music) test within the middle of the room (front of zone 5) to capture the C-weighted average SPL for the entire room. Note that the C-weighted target is approximately 52dB, compared to the A-weighted target of 36dB mentioned previously.