What I do believe is that there is an artifact or artifacts.... and I
can hear them.
I put the LC filter as mentioned before on my headset and the so called
"artifacts" are gone.
It's very simple, I can't hear them with my ears if i have the LC filter
in irrespective of expensive equipment dB levels and measurements and
perhaps they are 70dB down but there is something there and I'm not the
only one to hear it.
My hearing is good up and beyond 12KHz, perhaps that is part of my problem.
There is also no filtering on the circuit from the DAC to the audio amp
as far as I can seeso everything coming out from the DAC is amplified.
73's
Berni
G0IDA
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.
/>/ /
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