Comparison of background noise

Here is my attempt to better illustrate the difference in signal-to-noise of the two recorded signals.

First I performed a high-pass filter operation on the waveforms of the first two transmissions. This was to focus a little more on the noise and less on the complex voice waveform. Analyzing the resulting waveform did not reveal a visually significant difference between the two operators' signals.

Next I selected a segment of the waveform between words and performed an FFT operation. The resulting displays show the levels vs frequency. The top graph is from the recording of WA5MLF's transmission, and the bottom is from KB4PYR.

The sharp peak around 6 to 7 kHz is from aliasing and should be ignored. Looking at the graphs in the 1200 to 2400 Hz range reveals a higher level on the recording of WA5MLF's signal, which I think represents its higher noise level relative to the voice peaks. Click on the figure to expand it for better viewing. I believe the noise is higher for WA5MLF due to the receiver's AGC allowing more gain on average during the voice transmission, allowing greater amplification of the background noise.

The FFT graphs shown here were produced by the Cool Edit 2000 program which was acquired by Adobe and is now part of their Audition product offering. An equivalent FFT graph can be produced with the free Audacity program, which also provides a text export of the data to be plotted with the software of your choice.