K3 RF speech processor > aliasing ?
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Hi All,
Yesterday I sinned and whistled shortly into my microphone to see my watt meter reading. I apologize for this bad bad operator habbit... To my surprise I heard a second whistle monitoring the signal.When I whistled "up" the other whistle was going down in frequency, when I whistled "down" the byproduct was going up. It seems like there is a quite strong aliasing (mirroring against nyquist freq) product in my TX audio. First I suspected the clock of the A-D converter of the ingoing audio. Fortunately there is no aliasing at all with the RF processor turned off. Is this exemplary for my K3 or do others also notice this aliasing in the RF processor? It's easy to test copying my bad behaviour (in "TX test mode"!!) monitoring yourself. I wonder if there is any 1/2 nyquist filtering in the RF processor algorithm, and what the actual sampling rate of the RF processed TX signal is. Listening to the aliasing products samplerate seems pretty low. Also wonder what this does to the TX audio spectrum, though I assume the aliasing products do not exceed the TX passband in final transmitted signal. 73' Paul PD0PSB |
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Correction on the above (should dust off the old books some day...)
I wonder if there is any 1/2 nyquist filtering (should be 1/2 Fs filtering) in the RF processor algorithm, and what the actual sampling rate (should be samplingfrequency) of the RF processed TX signal is. 73' Paul PD0PSB |
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In reply to this post by pd0psb
Hello Paul!
> Yesterday I sinned and whistled shortly into my microphone to see my watt > meter reading. I apologize for this bad bad operator habit... > > To my surprise I heard a second whistle monitoring the signal. When I > whistled "up" the other whistle was going down in frequency, when I whistled > "down" the byproduct was going up... > > Fortunately there is no aliasing at all with the RF processor turned off. I ran some tests here this morning regarding this. The MON function, which allows you to hear your transmitted audio, is the source of the aliasing artifact you are hearing. I deliberately removed most filtering from the demodulator to minimize delay. The downside is lack of alias suppression. In my radio, I only hear this if I whistle and have CMP set to a very high value -- 20 or more. At normal CMP levels (15 or less)I don't hear it, and never hear it with speech. I also confirmed that this aliasing product does not go over the air; it is local to the MON audio. I'll look into adding some filtering to reduce this effect and see if the resulting additional delay is acceptable. Meanwhile, your transmitted signal is clean! 73, Lyle KK7P ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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I have always found it a bit difficult to judge my own speech quality when
using the monitor function on any radio. Perhaps a substantial delay, several seconds, would be helpful in letting one listen to oneself after one has finished speaking. > I'll look into adding some filtering to reduce this effect and see if > the resulting additional delay is acceptable. > > Meanwhile, your transmitted signal is clean! > > 73, > > Lyle KK7P > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3 RF speech processor > aliasing ?
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Get the KDVR3, record an outgoing message, then monitor it being transmitted (and adjust settings to your liking) ;) ~Iain / N6ML Erik N Basilier wrote: > I have always found it a bit difficult to judge my own speech quality when > using the monitor function on any radio. Perhaps a substantial delay, > several seconds, would be helpful in letting one listen to oneself after one > has finished speaking. > >> I'll look into adding some filtering to reduce this effect and see if >> the resulting additional delay is acceptable. >> >> Meanwhile, your transmitted signal is clean! >> >> 73, >> >> Lyle KK7P >> > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by KK7P
Hello Lyle!
Tnx fr replying. I can confirm that the MON function is causing more aliasing. I cannot confirm that the artifacts are not in TX audio. With settings around CMP 10 I can start hearing "double whistle" aliasing monitoring on an ext receiver. Without RF processing the signal is very nice & clean. Also checked some "analog" counterparts of RF processing, which do not have this "mirroring" effect. I understand you have to find the best compromise between processing bandwidth and latency in K3 as a whole, but maybe the RF processor is a small bit too economic? 73' Paul PD0PSB <quote author="Lyle Johnson"> I ran some tests here this morning regarding this. The MON function, which allows you to hear your transmitted audio, is the source of the aliasing artifact you are hearing. I deliberately removed most filtering from the demodulator to minimize delay. The downside is lack of alias suppression. I also confirmed that this aliasing product does not go over the air; it is local to the MON audio. Meanwhile, your transmitted signal is clean! 73, Lyle KK7P |
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In reply to this post by K7TV
I also find listening to myself on the monitor a bit awkward because I hear
my voice by paths other than that of the radio. I think this can be largely overcome if you use the Voice Recorder and take a listen afterwards. The recorder is a very useful feature. I hope Elecrafter eventually provides a remote pod to activate the memories. 73 Doug EI2CN Subject: Re: [Elecraft] [K3] K3 RF speech processor > aliasing ? I have always found it a bit difficult to judge my own speech quality when using the monitor function on any radio. Perhaps a substantial delay, several seconds, would be helpful in letting one listen to oneself after one has finished speaking. > I'll look into adding some filtering to reduce this effect and see if > the resulting additional delay is acceptable. > > Meanwhile, your transmitted signal is clean! > > 73, > > Lyle KK7P > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Iain MacDonnell - N6ML-2
Thanks for the idea, but I don't use voice enough to justify a monitoring
solution that has a real cost to it. I don't think I would used the KDVR3 for any other purpose. On the other hand, if there will be a delay for purposes of anti-aliasing, that might solve the problem at no cost. The bottom line is I don't want to push to get something fancy like a menu-adjustable delay unless a lot of others want it too. 73, Erik K7TV > Get the KDVR3, record an outgoing message, then monitor it being > transmitted (and adjust settings to your liking) ;) > > ~Iain / N6ML ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by pd0psb
Hello Paul!
> I can confirm that the MON function is causing more aliasing. > I cannot confirm that the artifacts are not in TX audio. > With settings around CMP 10 I can start hearing "double whistle" aliasing > monitoring on an ext receiver. > Without RF processing the signal is very nice & clean. The purpose of the processor, of course, is to increase the average power of the signal while controlling the peak power. There will of necessity be distortion products when this is done. The operator of the radio needs to make choices and set the CMP level, etc., for the best results for his or her particular voice, band conditions, and operating objectives. We'll continue to work on improving the performance of the K3 speech processor. Meanwhile, many operators find it to be a very effective tool in their station operation. 73, Lyle KK7P ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Hi Lyle,
I agree that the RF processor certainly works and sounds well. The fact that I heard "double signals" of my whistling merely made me wonder where those "ghost signals" end up in the transmitted signal. I allways use very gentle processing (if at all) and that sounds fine. Tnx! 73' Paul PD0PSB Hello Paul! The operator of the radio needs to make choices and set the CMP level, etc., for the best results for his or her particular voice, band conditions, and operating objectives. We'll continue to work on improving the performance of the K3 speech processor. Meanwhile, many operators find it to be a very effective tool in their station operation. 73, Lyle KK7P ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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