> What I just wanted to point out is that not everything is > measurable... you can measure the group delay of a crystal > filter, but > in this case its effect is not so automatically stated. Different > group delays are perceived differently by different persons... there > is a theory that says that the human ears are not sensitive to the > relative phase between the various harmonics of a given sound, and > this has its roots on the working of the ear. But tests > performed by > the audiophiles revealed that a few persons as a matter of fact are > "phase deaf", while others are quite sensitive to it... so measuring > the group delay of a filter tells you nothing about how a given person > will judge the quality of that audio... as much as we all would like > to eliminate the subjective judgment from any objective measurement, > there are nevertheless things that escape a rigorous and instrumental > analysis... > > 73 Alberto I2PHD
There is something to it. From my experience with different operators and types of radios: I provided OK2RZ, who is one of the top contesters, with my modified Drake R4B, which had one 600 Hz "roofing" Xtal filter, then the LC IF etc. He loved it, smooth as a silk. Then he wanted modern radio, so there goes TS870 with modifications (better filters, gain distribution) and he "could not stand it". The problem? Apparently DSP and its digital demodulation, which made him uncomfortable with the sounds of weak signals. I could not tell that much difference and wondered what's with him :-) So I think the way DSP and its demodulation starts "chumping" on weak signals introduces some chopiness and has problem of discerning between wanted and unwanted stuff ....??? Now with direct conversion and SDRs, they are better in a sense that the Xtal filters with their delays and "smudging" of signals are eliminated, multiple noisy and hissy mixers are gone, so the radio made noise and delays/distortion is gone. With better A/D and D/A chips and super RF amps and mixers hitched to that SDR chain we have a winner at least for a while. I used SDR1000 in the contest for a while for monitoring and some RX functions, love it! This is the 5th (?) revolution in ham radio and thanks to all of you who are adding to it brick by brick. I am working on some ergonomics of controls and displays for the contesting and putting it in the integrated station package. 73 Yuri, K3BU
