[GreenKeys] Re: teletype machine noise levels

[w8au at sssnet.com]

At 05:14 PM 09/22/2004, Sam Hallas wrote:
  I had the same sort of confusion a while ago when I had to take some 
sound level measurements at work. Sound engineers talk a whole different 
language and also have two different reference points for their dB 
measurements with a difference of 94 dB if I recall!

You might be thinking of Sound Level readings vs. Noise Level 
readings.   The separation of the base measurement is 90 dB.
Sound level readings go above and below "Ø dBm" (1 mw) and can be either - 
or + this figure.   Noise level readings are always
based at -90 dBm, (noise floor) which in noise talk is "Ø dBrn" and are 
always measured as a +plus figure.

So.... a -45 dBm "audio level" reading of noise - is the same as +45 dBrn 
noise reading.

Confusing?  Yep.  Us electronics folk refer it to "telephone talk" and we 
had to always be careful when talking to telco
central offices.    We had always to instantly translate these telephone 
terms to electronics and reply back in telephone terms
to not confuse C. O. personnel.

But Ma Bell was the original source of many "sound level" measurements long 
before Audio engineers, and they are owed
some homage because of that.   (Grin and bear it)   :-)

Perry      w8au