Thursday, May 21, 2009

Compander Revisited

There was a recent discussion on EHAM regarding what the SDR sounded like when using the compander and the DX compander. I decided to make a couple of .avi clips to demonstrate what the compander does. Power SDR has built in a scope function that operates on both receive and transmit. Above is an example of what the signal looks like on transmit. You will also note near the bottom of the screen is a function called Gate. Next to Gate is a VU meter that represents the mic signal. I used this meter to keep the speech levels essentially constant during all runs. Watch the scope to clearly see what differences the various compander settings make. I made 3 runs one at 3 on each compander, one at 5 on each compander and one at 10 on each compander. You can judge for yourself how the compander works. If you watch you can see me switch each compander off and on.

level 3 run

level 5 run

level 10 run

The audio in these runs are without any pre-emphasis, which I usually add. My normal setup is to use just the compander with a setting of 2 and some upward sloping pre-emphasis. This increases the talk power without significant added distortion, but even at 10 the signal is very well behaved.