On Wed,9/21/2016 3:59 AM, Bill W4ZV wrote:
This is nothing new.  K3ZO has been doing this for about 30 years (at least)
using wide filters and his ears as DSP.  I did this long ago with a TS-930S
using SSB filters with CW VBT fully engaged which shifts two IF filters in
opposite directions giving a broad overall response but peaked in the
center.  See K3ZO's comments here:


Now we're getting to the good part of this thread, which I've found quite illuminating, because it explains user preferences for one radio over another that aren't obvious. Thanks to Will, Guy, and Bill for their very useful contributions to the discussion.

There's another VERY important factor related to bandwidth -- when we narrow the bandwidth to copy a very weak signal buried in noise (as opposed to QRM), the filter tends to ring at its skirts, making it more difficult to copy rather than easier. I find this to be true independent of which filter alignment I've chosen, and it's predicted entirely by classic filter theory. The K2, which sounds great when listening through its TX filter, has a multi-element crystal filter that it realigns to vary the bandwidth, sounds just awful when set for narrow SSB bandwidths. It's all due to the extreme phase shift in those filters.

As another example from my work in pro audio, I was hired to try to clean some really nasty buzz out of a "jailhouse" recording. This was in the late '70s, and DSP didn't exist. My tool was a very high quality, very narrow tunable notch filter with high and low pass filters, and I passed the recording though it a half dozen times to attack the harmonics of the buzz. With each pass, I reduced the buzz, but I also introduced more phase shift. So as the signal to noise improved, the intelligibility degraded.

73, Jim K9YC

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