[Elecraft] Re: Heil Proset & K3 Audio fixed, sort of.
Brendan Minish
ei6iz.brendan at gmail.com
Tue Sep 9 14:55:23 EDT 2008
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: elecraft-bounces at mailman.qth.net
> >> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jack Smith
> >> Sent: Tuesday, September 09, 2008 6:09 AM
> >> To: Dave G4AON
> >> Cc: elecraft at 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.
> >>> />/ /
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Don‘t complain. Nobody will understand. Or care. And certainly don‘t try
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