I fixed this in my headphones with an LC filter that takes the 12Khz trash down an additional 12dB I can easily hear the 12Khz stuff on good headphones at normal operating levels, even though it's at 60 to 70dB down on the desired audio. Because it's non-harmonically related it's impact on the perceived audio quality is much greater than harmonically related distortion.
I have very good hearing and worked for a few years as a professional sound engineer specialising in recording acoustic music. If you can't hear past 10Khz or your headphones have a restricted frequency range then this will be a non-issue. For me it was an irritant but by no means a show stopper, the K3 is a fine radio that sounds much nicer than my Icom's did However I am glad I invested the time to add LC filtering to my head set as the improvement is worthwhile. 73 Brendan EI6IZ On Tue, 2008-09-09 at 10:27 -0400, Jack Smith wrote: > I agree that it's around 70 dB below the normal signal level. > > The original poster believes it is the source of his problem. > > My ears are not good enough to hear 12 KHz. > > Jack K8ZOA > > > Joe Subich, W4TV wrote: > >> The 12 KHz artifact appears to be the audio output DAC clock, > >> with the demodulated audio forming upper and lower sidebands > >> with it. It's down considerably, but still is apparently > >> causing issues with those who have good high frequency hearing > >> response. > >> > > > > I'm confused ... my measurements show the "12 KHz artifact" is > > more than 70 dB below a 1V peak signal. The artifact is not > > measurable when the headphone level is below -30 dBV. This > > level is comparable to the in band receiver noise floor with a > > -73 dBm RF signal and below the in band noise level with -100 > > dBM (1 uV) or -130 dBm sources. I do not understand why an > > out of band signal some 70 dB down should be an issue. > > > > The only reason the 12 KHz artifact can even be noticed with > > test equipment is that the K3's out of band noise floor (noise > > above the DSP and IF cut-off) is so exceptional. Even with AF > > gain, the audio noise outside the passband is no more than -100 > > to -110 dBV (I can't measure it). > > > > To complete the record, the 12 KHz artifact is also present > > on the Line Out DAC about 70 dB below the desired signal. > > > > 73, > > > > ... Joe, W4TV > > > > > > > > > > > > > > > > > >> -----Original Message----- > >> From: [EMAIL PROTECTED] > >> [mailto:[EMAIL PROTECTED] On Behalf Of Jack Smith > >> Sent: Tuesday, September 09, 2008 6:09 AM > >> To: Dave G4AON > >> Cc: elecraft@mailman.qth.net > >> Subject: Re: [Elecraft] Re: Heil Proset & K3 Audio fixed, sort of. > >> > >> > >> The 12 KHz artifact appears to be the audio output DAC clock, > >> with the > >> demodulated audio forming upper and lower sidebands with it. > >> It's down > >> considerably, but still is apparently causing issues with > >> those who have > >> good high frequency hearing response. > >> > >> The K3's audio seems to have way too much high frequency > >> response, with > >> white noise visible up to 20 KHz and beyond in the headphone > >> and speaker > >> output ports. Most communications receivers roll off the > >> audio response > >> at a few KHz. > >> > >> A bit of roll off in the K3 would be beneficial, I think, > >> either RC or LC. > >> > >> Jack K8ZOA > >> > >> > >> Dave G4AON wrote: > >> > >>> Using Spectrum Lab with my "on motherboard" sound card shows a > >>> persistent artefact at 12 KHz with sometimes one either side of it. > >>> This doesn't appear when listening to typical speech on SSB > >>> > >> but tuning > >> > >>> to CW shows it, the signals either side of the 12 KHz one > >>> > >> are +/- the > >> > >>> tone of the CW signal, i.e. typically +/- 700 Hz. > >>> > >>> Audibly, there is more hiss and high frequency "roughness" when > >>> listening to CW signals with the K3 than listening to the > >>> > >> same signal > >> > >>> on a parallel connected K2 with it's AF DSP filtering, I would have > >>> hoped the RX equaliser would cut the high frequency signals but it > >>> doesn't. > >>> > >>> Looking at the circuit tends to suggest the place for a low pass > >>> filter would be the output of the DAC prior to the audio > >>> > >> amplfier at > >> > >>> "LHPOUT/RHPOUT" on the K3 DSP IF: DAC Audio board. Looking at the > >>> audio spectrum from my K3 (without FM) shows nothing above > >>> > >> 4 KHz, so a > >> > >>> low pass filter to cut everything above perhaps 5 KHz would do no > >>> harm. I am reluctant to modify my K3 unless it's an > >>> > >> official Elecraft > >> > >>> modification, but there is certainly some high frequency > >>> > >> audio present > >> > >>> that could do with removing. > >>> > >>> 73 Dave, G4AON > >>> K3/100 #80 > >>> -------------------- > >>> It suggests that perhaps you were hearing the artifacts > 4 > >>> > >> KHz, such > >> > >>> as the 12 KHz with modulation sidebands or the one at 3.9 > >>> > >> KHz. Maybe > >> > >>> you were not hearing the artifacts directly but beats amongst them? > >>> > >>> Jack K8ZOA > >>> > >>> Paul Fletcher wrote: > >>> > >>>> / In order to try and eliminate the objectionable "noise" (careful > >>>> > >>> avoidance of > >>> />/ distortion, harmonics etc deliberate) in my headset > >>> > >> I've fitted an > >> > >>> LC filter > >>> />/ with a 4kHz cut off. This would still pass odd order > >>> > >> harmonics for > >> > >>> lower > >>> />/ audio frequencies. This filter has totally eliminated > >>> > >> the annoying > >> > >>> "noise" I > >>> />/ was hearing with the downside that I have to run more > >>> > >> AF gain to > >> > >>> compensate. > >>> />/ This kind of backs up previous measurements made by > >>> > >> others that the > >> > >>> />/ harmonics are well down, and not noticeable. It's a bit > >>> disappointing that I > >>> />/ had to do this but the headphone audio is now very nice indeed. > >>> />/ / > >>> _______________________________________________ > >>> Elecraft mailing list > >>> Post to: Elecraft@mailman.qth.net > >>> You must be a subscriber to post to the list. > >>> Subscriber Info (Addr. Change, sub, unsub etc.): > >>> http://mailman.qth.net/mailman/listinfo/elecraft > >>> Help: http://mailman.qth.net/subscribers.htm > >>> Elecraft web page: http://www.elecraft.com > >>> > >>> > >> _______________________________________________ > >> Elecraft mailing list > >> Post to: Elecraft@mailman.qth.net > >> You must be a subscriber to post to the list. > >> Subscriber Info (Addr. Change, sub, unsub etc.): > >> http://mailman.qth.net/mailman/listinfo/elecraft > >> > >> Help: http://mailman.qth.net/subscribers.htm > >> Elecraft web page: http://www.elecraft.com > >> > > > > > > > _______________________________________________ > Elecraft mailing list > Post to: Elecraft@mailman.qth.net > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com -- Don‘t complain. Nobody will understand. Or care. And certainly don‘t try to fix the situation yourself. It‘s dangerous. Leave it to a highly untrained, unqualified, expendable professional. _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
