IF Noise Reduction
IF noise reduction removes noise before a signal enters the demodulator. This can improve the noise level better than using AF noise reduction due to the way demodulators can further remove noise in the demodulation process.
In SDR# The options the user is presented with are:
This is a setting you will be adjusting the most. This option sets the point that noise is removed. This is ideally set a fraction above the noise floor (Or the noisiest part of the signal, for example noise jumps due to RFI or lightning)
This is how deep the NR goes aka how much noise is reduced by.
Slope is the knee of the NR and it seems to affects the harshness of what levels get removed by how much. Too steep and it sounds artifact-y, too light and it’s not removing enough noise!
Smoothing makes the signal sound smoother and less harsh. From my testing, it adds in some quiet fuzz to soften the noise gates opening and closing and usually makes the experience nicer.
Attack & Release
These 2 options set the time it takes for the noise gates to open and close. Tighter timing lets through less noise but more artefacts, looser timing lets through more noise but isn’t as harsh. My go-to timings are 30ms Attack, 70ms Release.
More FFT resolution = better is usually the rule of thumb. This affects the number of noise gates available.
2048 and 4096 are the ideals for me and I always run at 4096 but the speed of your CPU will affect this choice.