[TenTec] NB verses NR

[Carl Moreschi]

There seems to be lots of confusion on the difference between NB and NR. 
  They do very different jobs.

Noise Blanker (NB) is a classic function that goes way back to at least 
the early 1950's.  What it does is look for a very sharp leading edge on 
noise and actually blank out audio for the duration of the steep noise 
spike.  With repetitive noise like from a motor or an arcing insulator 
on a power poll, the audio will get muted for a few milliseconds then 
come back on.  With the right kind of noise the noise can sometimes be 
completely eliminated with the function. I have seen as much as a 20 db 
improvement with signal to noise ratio using this function with the 
right kind of noise. The side affect of this is the noise can become 
modulated with a strong signal on the band that will remove the noise 
blanker from detecting noise since it the noise blanking detection can 
get swamped with a strong signal.  This will sound like noise coming on 
and off.  Because of this, SSB can sometimes also become distorted.

Noise Reduction (NR) is a completely different function.  It has only 
been around since DSP starting becoming used in radios.  It works by 
attempting to find an algorithm that can identify speech and try to 
remove audio not detected as speech.  There are many different 
algorithms for this with many manufacturers having their own proprietary 
algorithm.  Although this function can make the radio quieter, I have 
never found a case on any radio where copy was actually improved by this 
function.

Carl Moreschi N4PY
58 Hogwood Rd
Louisburg, NC 27549
www.n4py.com