Guys... Hold on... I have my reasons... Hear me out...
>Why pre-DSP? Maybe I should have said "Before the input of the active audio processing area in the DSP section of the radio". That is, a way to control analog "dynamic range" at the input of the RF Clipper section of the DSP audio chain. What I was suggesting is an AGC funtion before the RF Clipping section touches the audio waveform. Something to smooth out the dynamic range of the audio input so that the DSP processing engine would not have to work so hard dealing with peaks and valleys and can be "let loose" some. The K3's DSP audio management software understands the Nyquist Limit of its ADC, and it plays a very conservative game :) The RF Clipper does a good job of controlling these, always keeping them within the ADC's non distorting range, but nothing is perfect. If you hit the input stage too hard (ever get excited calling a DX Station or a Multiplier?) the clipper grabs the peak, which then reduces the overall audio level. Since the decay value is somewhat slower than the attack, you end up "punching a hole" in the audio. Im really nitpicking here... Its really minor, but I notice it and have learned to live with it. But it *IS* there. >He can do that in firmware. Thats just fine with me. I dont care if he does it with Squirrels on a treadmill, if it can be done, Im all for it! >You can forget about a hardware mod. I was not aware that I was requesting a hardware mod. Where did you get that idea? I dont care how its done. I just hope that it *CAN* be done. >Why do we keep trying to remake a digital radio into an analog radio? I was not aware that only *analog* radios had an AGC ahead of a limiter. I know many broadcast digital processors that have these features incorporated in software. You can always go to the nearest pawn shop and buy a Aphex Compellor and a mic preamp and do the same thing. Just would be nice to have it all in one box. >A DSP version can have options. Exactly! This is just one more option! >Just has to get in line with all the other things taking resources in a small business. I have no problem with that. K3 is not broken, Im not trying to fix it. Just in my opinion this would be a very useful feature. Its up to Wayne and his staff to make the ultimate decision. If I want to fix it, I have to dust off my Compellor and add some complexity to my station. I dont want to do that. > >How do you define "headroom"? > The difference between when the input to the DSP is at its highest point (100% signal saturation) and the point where the input waveform clips appreciably (usually 10% above full modulation is a standard measurement) in an RMS waveform. Remember we are using a ADC here. It QUANTIZES the analog waveform in finite steps (254? 1024? Only Lyle knows what he has implemented). If its, for example, 0 to 254, then 255 is distortion because the value is undefined and is truncated in the quantization matrix. You have hit the Nyquist wall! For instance, in professional digital videotape machines, maximum level is defined as -20dB (-20dB = 0VU in analog) and "saturation" is defined as 0dB (the "clip point" in analog). The difference between these levels is defined as "headroom" (the "Nyquist limit") for those RMS peaks that happen in wide dynamic range material. Back in the analog days we would use 0VU as the RMS reference level, but the peaks could go all the way into the red without distorting... But then analog systems went into distortion "gracefully" a lot higher than 0VU; they never run out of numbers (reach the "Nyquist" limit), but they do run out of the linear curve of the active devices in the circuit. Digital systems just clip when they run out of numbers, so there is no margin for error, hence the "digital overhead to account for analog dynamic range" built in to digital audio recorders. What Im saying is that since the difference in the K3 is somewhat narrow, because we are playing conservatively, in my opinion (I have not done quantitative testing, Its just my "by ear" opinion), if there were some "dynamic range leveling" before the ADC, it would be helpful to the overall system efficiency. I will shut up now, learn not to yell into the mic or go plug in my Compellor :) -lu-w4lt- ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
