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On bands like 10m when there is often little or no QRM (just gaussian noise), are the "Noise Reduction" filters intended to make weak phone signals more understandable? My subjective view is that I can understand the voice better without the filter, but it less comfortable.

Edit to add: my radio is an IC-7300. I thought that perhaps it is common practice to not use those filters for weak phone signals. When I'm trying to make a QSO with such a station, probably at the bottom of the pile-up, I have lots of time to think about filters :)

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    $\begingroup$ There's some interesting info on the DSP SE: how do noise reduction filters work $\endgroup$
    – webmarc
    Apr 20 at 0:35
  • $\begingroup$ No operational experience, especially on 10m, on my side, but do you happen to have a transmit-capable SDR and enough attenuators, with which you could test performance? $\endgroup$ Apr 21 at 22:43

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Yes, Noise reduction can help if there is just a fair amount of QRN (AGWN, etc.) and no QRM, depending on the type of NR.

There are many different NR algorithms, including using AI/ML and/or Spectral subtraction. Spectral subtraction can be implemented using a non-linear algorithm which does voice activity detection, continuously (or at small time quantums) characterizing which frequencies are part of the human voice portion of the signal, and which are not. Then the algorithm uses adaptive DSP filtering to spectrally subtracts those portions of the spectrum (via FFT overlap processing) which the algorithm estimates/guesses are not part of the human voice input. If those portions of the estimated/guessed non-voice spectrum are just noise, then noise is reduced. If the algorithm's estimate/guess is wrong, then there will be artifacts and distortion.

However, whether or not it is easier, or less tiring, to copy a QSO with or without the estimated noise subtracted is sometimes stated to be a personal preference. Some operators claim their own brain can do a better job of ignoring noise.

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