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K7TV

OT - sound cards

I have never expected standard sound cards to be really good, but I have
nevertheless used them successfully for purposes like digital modes. When I
built a SoftRock I got an E-MU 0202 for the higher sampling frequency. When
I sold my LP-PAN and SoftRock, the E-MU went with them. My current main
computer is a high-end HP desktop running Windows 7, a little over a year
old. The output sound quality is not bad, but not until recently did I use
the microphone input for anything. Then I suddenly needed to make some voice
recordings using a microphone. Every recording has terrible background noise
which is not being picked up by the mike, an has nothing to do with
grounding etc. The noise is a mix of white (or is it pink?) noise with added
irregular frying-pan crackle and some mosquito whine. It is the same with
different microphones, and increased microphone output doesn't help because
the noise is not reduced when the software mike gain is reduced. Overall,
the S/N is worse than for the average landline telephone call (but of course
the latter at times has distortion that is much worse than the computer's).
Curious, I took the same microphones to my old XP laptop. It had much less
noise! To perfect the comparison I then went to adjust the mike gain in the
XP software. Hmmm. there is a checkmark in a box for noise reduction. I
unchecked it, and now the laptop had a lot of noise, but not quite as much
as the desktop. Then I went to the desktop to look for a noise reduction
option. I found it and turned it on. Big improvement. Now the noise is low
enough for my voice recording purposes. However, the noise reduction causes
very obvious artifacts similar to ones often found in HAM radio noise
reduction. The noise reduction on the old laptop seemed better in this
respect.

At this point I obviously don't know everything that is going on, but I have
seen enough to have a gut feel. So, I will lay out my thoughts to the group,
and hope that others will fill in the blanks and correct me where I may be
jumping to conclusions. Here are my current thoughts:

. It is somewhat difficult to keep noise out of a low-level audio
circuit that is sitting next to a lot of high-speed digital circuitry, as on
a PC motherboard (there is no separate sound card in this PC).

. Rather than spend the extra bucks for physical separation or
shielding, etc, PC manufacturers routinely ignore the noise issues, and
cover them up with noise reduction algorithms, which get more aggressive as
the noise environment inside PC's gets worse.

. Other brands of computers are probably just as bad (or can someone
recommend a brand that comes with low noise audio as standard?).

. If I get another external USB sound card of good quality, I should
definitely not limit its use to soundcard-dependent SDR's, but use it for
digital modes too.

. If I do use an internal soundcard for digital modes again, I had
better make sure that the noise reduction in the PC is turned off, as noise
reduction is known to be incompatible with digital modulation schemes.

. As if I didn't know it already, Elecraft has it right when they
don't make their radios rely on computer sound cards!

73 And thanks in advance,

Erik K7TV

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David Gilbert

Re: OT - sound cards

If you can't even make decent quality voice recordings, you have
something else wrong. Unless it is simply defective, even the cheapest
sound chip out there isn't going to act like you describe.

And what exactly do you think the I/Q outputs of the KX3 are going to be
using?

Dave AB7E

On 1/8/2012 11:24 PM, Erik Basilier wrote:

> I have never expected standard sound cards to be really good, but I have
> nevertheless used them successfully for purposes like digital modes. When I
> built a SoftRock I got an E-MU 0202 for the higher sampling frequency. When
> I sold my LP-PAN and SoftRock, the E-MU went with them. My current main
> computer is a high-end HP desktop running Windows 7, a little over a year
> old. The output sound quality is not bad, but not until recently did I use
> the microphone input for anything. Then I suddenly needed to make some voice
> recordings using a microphone. Every recording has terrible background noise
> which is not being picked up by the mike, an has nothing to do with
> grounding etc. The noise is a mix of white (or is it pink?) noise with added
> irregular frying-pan crackle and some mosquito whine. It is the same with
> different microphones, and increased microphone output doesn't help because
> the noise is not reduced when the software mike gain is reduced. Overall,
> the S/N is worse than for the average landline telephone call (but of course
> the latter at times has distortion that is much worse than the computer's).
> Curious, I took the same microphones to my old XP laptop. It had much less
> noise! To perfect the comparison I then went to adjust the mike gain in the
> XP software. Hmmm. there is a checkmark in a box for noise reduction. I
> unchecked it, and now the laptop had a lot of noise, but not quite as much
> as the desktop. Then I went to the desktop to look for a noise reduction
> option. I found it and turned it on. Big improvement. Now the noise is low
> enough for my voice recording purposes. However, the noise reduction causes
> very obvious artifacts similar to ones often found in HAM radio noise
> reduction. The noise reduction on the old laptop seemed better in this
> respect.
>
>
>
> At this point I obviously don't know everything that is going on, but I have
> seen enough to have a gut feel. So, I will lay out my thoughts to the group,
> and hope that others will fill in the blanks and correct me where I may be
> jumping to conclusions. Here are my current thoughts:
>
>
>
> . It is somewhat difficult to keep noise out of a low-level audio
> circuit that is sitting next to a lot of high-speed digital circuitry, as on
> a PC motherboard (there is no separate sound card in this PC).
>
> . Rather than spend the extra bucks for physical separation or
> shielding, etc, PC manufacturers routinely ignore the noise issues, and
> cover them up with noise reduction algorithms, which get more aggressive as
> the noise environment inside PC's gets worse.
>
> . Other brands of computers are probably just as bad (or can someone
> recommend a brand that comes with low noise audio as standard?).
>
> . If I get another external USB sound card of good quality, I should
> definitely not limit its use to soundcard-dependent SDR's, but use it for
> digital modes too.
>
> . If I do use an internal soundcard for digital modes again, I had
> better make sure that the noise reduction in the PC is turned off, as noise
> reduction is known to be incompatible with digital modulation schemes.
>
> . As if I didn't know it already, Elecraft has it right when they
> don't make their radios rely on computer sound cards!
>
>
>
> 73 And thanks in advance,
>
> Erik K7TV
>
>
>
> ______________________________________________________________
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> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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>

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K7TV

OT - sound cards

In reply to this post by K7TV

Dave, "decent quality" may be a somewhat subjective concept. Without the
software noise reduction in the computer, the microphone recordings sound
very good, except for that noise which is noticeable in pauses. With noise
reduction on, the situation is reversed: Low noise during pauses, almost
like a noise gate, but artifacts during words. To be more precise about the
artifacts, I don't notice a great deal of reduction in higher audio
frequencies as has sometimes been observed in radios' noise reduction
algorithms, but mostly a metallic twang, similar to "robot speech" in an old
sci-fi movie, which is most obvious at start of recording and at the end of
words, where the speech signal level is close to zero. (This is all using
the standard Sound Recorder that comes with Windows 7.)

The KX3 I/Q outputs may for all I know have sufficient levels that they can
feed the sound card's line input. That input doesn't necessarily have the
same noise problem as does the microphone input; I have never tried the line
input on this rather new PC. To clarify, when I referred to past digital
mode usage, it was not on this computer but on either an older desktop or on
the old laptop. As I recall from the small number of qso's using the laptop,
the results may have been inferior on receive compared to the old desktop,
which had a mid-level brand name PCI soundcard.

I don't think it fair to expect Elecraft to somehow guarantee that a user
who wants to make use of the KX3 I/Q outputs will get optimal results with
all computers' sound cards. For starters, most laptops obviously won't do
the job without an external soundcard, since they don't have stereo inputs.
I would expect that a good internal sound card will do a better job than
most motherboard-integrated "sound cards", and that a good external one will
perform best, even if one doesn't need a high sampling frequency for a given
application.

I would not assume that the noise performance of the microphone input is
determined by the quality of the sound chip, but that the layout of the
card, as well as decoupling and isolation components play a significant role
in preventing sub-millivolt noise signals from entering the signal chain at
some point before digitization.

73,

Erik K7TV

>If you can't even make decent quality voice recordings, you have something
else wrong. Unless it is simply defective, even the cheapest sound chip out
there isn't going to act like you describe.

And what exactly do you think the I/Q outputs of the KX3 are going to be
using?

Dave AB7E

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Joe Subich, W4TV-4

Re: OT - sound cards

Eric,

Sound facilities integrated on computer main boards - both "desk" and
laptop systems - are notorious for noise issues. Mainboard designers
simply do not have the experience in keeping signal lines "clean" and
doing the level of bypassing/decoupling necessary to maintain power
supplies clean enough for audio (analog) signals. They have gotten
sloppy since the digital domain is much more forgiving of "low level"
noise.

Fortunately or unfortunately depending on one's point of view, the
sloppy audio practices are a primary reason that external audio devices
tend to provide a much higher level or performance today. That has not
always been the case and some PCI/PCI-E sound cards go to extraordinary
lengths to clean up the power supply to avoid the problems.

73,

... Joe, W4TV

On 1/9/2012 10:50 AM, Erik Basilier wrote:

> Dave, "decent quality" may be a somewhat subjective concept. Without the
> software noise reduction in the computer, the microphone recordings sound
> very good, except for that noise which is noticeable in pauses. With noise
> reduction on, the situation is reversed: Low noise during pauses, almost
> like a noise gate, but artifacts during words. To be more precise about the
> artifacts, I don't notice a great deal of reduction in higher audio
> frequencies as has sometimes been observed in radios' noise reduction
> algorithms, but mostly a metallic twang, similar to "robot speech" in an old
> sci-fi movie, which is most obvious at start of recording and at the end of
> words, where the speech signal level is close to zero. (This is all using
> the standard Sound Recorder that comes with Windows 7.)
>
>
>
> The KX3 I/Q outputs may for all I know have sufficient levels that they can
> feed the sound card's line input. That input doesn't necessarily have the
> same noise problem as does the microphone input; I have never tried the line
> input on this rather new PC. To clarify, when I referred to past digital
> mode usage, it was not on this computer but on either an older desktop or on
> the old laptop. As I recall from the small number of qso's using the laptop,
> the results may have been inferior on receive compared to the old desktop,
> which had a mid-level brand name PCI soundcard.
>
>
>
> I don't think it fair to expect Elecraft to somehow guarantee that a user
> who wants to make use of the KX3 I/Q outputs will get optimal results with
> all computers' sound cards. For starters, most laptops obviously won't do
> the job without an external soundcard, since they don't have stereo inputs.
> I would expect that a good internal sound card will do a better job than
> most motherboard-integrated "sound cards", and that a good external one will
> perform best, even if one doesn't need a high sampling frequency for a given
> application.
>
>
>
> I would not assume that the noise performance of the microphone input is
> determined by the quality of the sound chip, but that the layout of the
> card, as well as decoupling and isolation components play a significant role
> in preventing sub-millivolt noise signals from entering the signal chain at
> some point before digitization.
>
>
>
>
>
> 73,
>
> Erik K7TV
>
>
>
>> If you can't even make decent quality voice recordings, you have something
> else wrong. Unless it is simply defective, even the cheapest sound chip out
> there isn't going to act like you describe.
>
>
>
> And what exactly do you think the I/Q outputs of the KX3 are going to be
> using?
>
>
>
> Dave AB7E
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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K7TV

OT - sound cards

In reply to this post by K7TV

My apologies - I forgot to put the subject on the post I just sent.

-Erik K7TV

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alorona

Re: OT - sound cards

In reply to this post by K7TV

Hi, Eric,

A lot of computers (especially HP) are notorious for that. It is a hardware
design flaw as Joe W4TV has described.

If you disconnect the power supply from your laptop (i.e. run on battery power)
and try it again you'll probably notice a significant improvement in the noise
level of your recorded audio. What does that tell you?

I had to resort to using an external sound card to digitize audio and then suck
it into the computer via USB. Something like the M-Audio or similar devices that
you can find at Guitar Center for recording musical instruments. Using one of
these the audio is clean. Good luck in your efforts.

Regards,

Al W6LX
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Jim Brown-10

Re: OT - sound cards

On 1/9/2012 10:29 AM, Al Lorona wrote:
> If you disconnect the power supply from your laptop (i.e. run on battery power)
> and try it again you'll probably notice a significant improvement in the noise
> level of your recorded audio. What does that tell you

It certainly tells us that the product is badly built from a bonding
point of view, and probably has severe Pin One problems. This is one of
many problems that can be solved by proper bonding from computer chassis
to rig chassis, as described in my tutorial, referenced in the previous
email.

73, Jim K9YC

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Jim Dunstan

Re: OT - sound cards

In reply to this post by alorona

At 01:29 PM 1/9/2012, you wrote:

Hi,

My observation of built in sound cards both desktop (also an HP) and
laptop (Asus netbook) is that they are not very good from a noise
point of view. I have acquired an M-Audio D-44 which i use in my
station desktop computer. It is a PCI card with an external breakout
box .... making it very convenient from a radio shack point of
view. The radio can be almost 5' away from the computer.

I have compared it to built in sound cards for recording and digital
operations. The D-44 is clearly superior. When operating digital
modes I have compared it to the built in sound cards as well as the
external units such as the Signalink. The waterfall on the screen is
best with the D-44 ... by a long shot ... even when compared to the
external units like the Signalink. The M-Audio was originally used
by me for music recording ... then it was recruited for my early SDR
experiments ... and now it is used for digital mode radio
operations. The only shortcoming is that it is far from portable
hi. The little Signalink works well with my laptop for portable work
... but not quite as clean as my D-44.

M-audio still makes good sound cards (the D-44 is now obsolete).

Jim, VE3CI

>A lot of computers (especially HP) are notorious for that. It is a hardware
>design flaw as Joe W4TV has described.
>
>If you disconnect the power supply from your laptop (i.e. run on
>battery power)
>and try it again you'll probably notice a significant improvement in
>the noise
>level of your recorded audio. What does that tell you?
>
>I had to resort to using an external sound card to digitize audio
>and then suck
>it into the computer via USB. Something like the M-Audio or similar
>devices that
>you can find at Guitar Center for recording musical instruments. Using one of
>these the audio is clean. Good luck in your efforts.
>
>Regards,
>
>Al W6LX

K7TV

OT- sound cards

In reply to this post by K7TV

Hi Jim VE3CI, and thanks for your comments.

I think it was a D-44 that I used years ago for a music computer setup. It
was a card connected to a big external dongle.

AFAI remember I had no problem with noise, but I didn't use any microphone
level signals. I could obviously dig it up and put it in my current main
computer if there is a Win 7 driver for it. I freely admit to trying to
benefit from others' experience before expending my own elbow grease ...

-Erik K7TV

Hi,

My observation of built in sound cards both desktop (also an HP) and laptop
(Asus netbook) is that they are not very good from a noise point of view. I
have acquired an M-Audio D-44 which i use in my station desktop computer.
It is a PCI card with an external breakout box .... making it very
convenient from a radio shack point of view. The radio can be almost 5'
away from the computer.

I have compared it to built in sound cards for recording and digital
operations. The D-44 is clearly superior. When operating digital modes I
have compared it to the built in sound cards as well as the external units
such as the Signalink. The waterfall on the screen is best with the D-44 ...
by a long shot ... even when compared to the external units like the
Signalink. The M-Audio was originally used by me for music recording ...
then it was recruited for my early SDR experiments ... and now it is used
for digital mode radio operations. The only shortcoming is that it is far
from portable hi. The little Signalink works well with my laptop for
portable work ... but not quite as clean as my D-44.

M-audio still makes good sound cards (the D-44 is now obsolete).

Jim, VE3CI

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alorona

Re: OT - sound cards

In reply to this post by Jim Brown-10

No, I'm afraid that what I'm talking about is the crosstalk between power supply
noise and audio circuits is occurring inside the computer, not between the
computer and rig. It's a hardware design flaw that no amount of bonding is going
to cure. The noise I'm talking about is there if you use the built-in mic on the
laptop. Believe me, I tried all according to the K9YC bible which has been an
invaluable aid over the years.

Al W6LX

________________________________
> This is one of many problems
> that can be solved by proper bonding
> from computer chassis to rig chassis,
> as described in my tutorial, referenced
> in the previous email.

73, Jim K9YC
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Jim Dunstan

Re: OT- sound cards

In reply to this post by K7TV

At 02:14 PM 1/9/2012, you wrote:

>I think it was a D-44 that I used years ago for a music computer setup. It
>was a card connected to a big external dongle.

yes, the breakout box was on the end of a 5' cable and used 1/4"
jacks (8 of them) !!

>AFAI remember I had no problem with noise, but I didn't use any microphone
>level signals. I could obviously dig it up and put it in my current main
>computer if there is a Win 7 driver for it. I freely admit to trying to
>benefit from others' experience before expending my own elbow grease ...
>
>-Erik K7TV

I find the M-Audio web site very good for software support. I would
not be surprised if they have W7 drivers and interface for the D-44.

Jim, VE3CI

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Mike Reublin

Re: OT - sound cards

In reply to this post by Jim Brown-10

How does one bond a flaptop? Most of the Win machines I've seen have a plastic case.
My Macbook Pro has a metal case, but the screws that hold the bottom cover are tiny.

73, Mike NF4L

On 1/9/2012 1:40 PM, Jim Brown wrote:

> On 1/9/2012 10:29 AM, Al Lorona wrote:
>> If you disconnect the power supply from your laptop (i.e. run on battery power)
>> and try it again you'll probably notice a significant improvement in the noise
>> level of your recorded audio. What does that tell you
> It certainly tells us that the product is badly built from a bonding
> point of view, and probably has severe Pin One problems. This is one of
> many problems that can be solved by proper bonding from computer chassis
> to rig chassis, as described in my tutorial, referenced in the previous
> email.
>
> 73, Jim K9YC
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
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k6dgw

Re: OT - sound cards

On 1/9/2012 2:00 PM, Mike wrote:
> How does one bond a flaptop? Most of the Win machines I've seen have a plastic case.
> My Macbook Pro has a metal case, but the screws that hold the bottom cover are tiny.

It can be hard to find metal. My laptop has a DB-15F for an external
monitor or projector on the side, and I get a chassis connection there
using a short screw in one of the two tie-down nuts. Seems to work fine.

FWIW: Youngest son and family gave me the Steve Jobs biography for
Christmas. I'm about half way through, but far enough to understand
that Jobs very specifically intended that users not be able to take the
Mac apart, to the extent that they used some screws that required a
special tool. Don't know about the Macbook Pro, but if I had one, I
don't think I'd take the screws out. He was pretty paranoid about this
... it might self-destruct. :-)

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2012 Cal QSO Party 6-7 Oct 2012
- www.cqp.org

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alorona

Re: OT - sound cards

In reply to this post by Mike Reublin

Shell of one of the metal connectors; or use a cable in the cable-lock jack.

> How does one bond a flaptop?
> 73, Mike NF4L
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David Gilbert

Re: OT - sound cards

In reply to this post by K7TV

OK, now that sounds a lot like the issues I had when I first began using
pre-recorded .wav files for contesting. I got several reports of "hum",
"noise", or "whine" on my transmitted signal ... all of which went away
when I disconnected the RS-232 cable from between the computer and the
K3. As I have mentioned several times here before, it took a very short
piece of shielded braid between the chassis of the K3 and the chassis of
the computer to fix it so that I could reconnect the RS-232 cable
without issues. I started with a couple of feet of braid and had to go
all the way down to eight inches before I could no longer notice the
problem.

You don't say what measures you've taken to bond the chassis of your K3
to your computer, but that would be my first suggestion. Your symptoms
sound almost identical ... even with respect to the noise during pauses
and the metallic twang at the end of words.

Regarding sound cards for SDR use, certainly the great majority of cards
out there would have major deficiencies ... most especially for noise,
but also for dynamic range and sampling rate. And as you say, many
don't even have stereo inputs. N8LP keeps a list of recommended cards
on his web site with good information on the pros and cons of each.

73,
Dave AB7E

On 1/9/2012 8:50 AM, Erik Basilier wrote:

Bill K9YEQ

Re: OT - sound cards

In reply to this post by k6dgw

Fred,

When I have to work on one, I have to carefully lay out the screws during
removal to help remember where to reinstall them. None are the same size!
I replaced a G4 PowerBook HDD and it took much longer than a Toshiba laptop
of same vintage. I use Toshiba as an example as they used to be a
nightmare. Older keyboard, track pads on laptops remain a tech level task.
Most Laptop PC's today have simple access to RAM, HDD and Keyboards which is
quite a quick task for a tech. Steve didn't want anyone to know what he had
inside, the components are nothing special, just a pretty face. ( I am ready
for flaming, have my suit on. :-))

73,
Bill
K9YEQ

-----Original Message-----

On 1/9/2012 2:00 PM, Mike wrote:
> How does one bond a flaptop? Most of the Win machines I've seen have a
plastic case.
> My Macbook Pro has a metal case, but the screws that hold the bottom cover
are tiny.

It can be hard to find metal. My laptop has a DB-15F for an external
monitor or projector on the side, and I get a chassis connection there using
a short screw in one of the two tie-down nuts. Seems to work fine.

FWIW: Youngest son and family gave me the Steve Jobs biography for
Christmas. I'm about half way through, but far enough to understand that
Jobs very specifically intended that users not be able to take the Mac
apart, to the extent that they used some screws that required a special
tool. Don't know about the Macbook Pro, but if I had one, I don't think I'd
take the screws out. He was pretty paranoid about this ... it might
self-destruct. :-)

73,

Fred K6DGW

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Bill K9YEQ

Re: OT - sound cards

The "...simple access to RAM... " etc. should read simple task for a tech.

73,
Bill
K9YEQ

-----Original Message-----

Fred,

When I have to work on one, I have to carefully lay out the screws during
removal to help remember where to reinstall them. None are the same size!
I replaced a G4 PowerBook HDD and it took much longer than a Toshiba laptop
of same vintage. I use Toshiba as an example as they used to be a
nightmare. Older keyboard, track pads on laptops remain a tech level task.
Most Laptop PC's today have simple access to RAM, HDD and Keyboards which is
quite a quick task for a tech. Steve didn't want anyone to know what he had
inside, the components are nothing special, just a pretty face. ( I am ready
for flaming, have my suit on. :-))

73,
Bill
K9YEQ

-----Original Message-----

On 1/9/2012 2:00 PM, Mike wrote:
> How does one bond a flaptop? Most of the Win machines I've seen have a
plastic case.
> My Macbook Pro has a metal case, but the screws that hold the bottom
> cover
are tiny.

It can be hard to find metal. My laptop has a DB-15F for an external
monitor or projector on the side, and I get a chassis connection there using
a short screw in one of the two tie-down nuts. Seems to work fine.

FWIW: Youngest son and family gave me the Steve Jobs biography for
Christmas. I'm about half way through, but far enough to understand that
Jobs very specifically intended that users not be able to take the Mac
apart, to the extent that they used some screws that required a special
tool. Don't know about the Macbook Pro, but if I had one, I don't think I'd
take the screws out. He was pretty paranoid about this ... it might
self-destruct. :-)

73,

Fred K6DGW

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Don Wilhelm-4

Re: OT - sound cards

In reply to this post by David Gilbert

Dave and all,

It is my understanding that the bandwidth of the KX3 I/Q outputs will be
"greater than 40 kHz", but certainly less than the 200 kHz width of the P3.

That fact reduces the sampling rate requirements of the sound card - I
believe most on-motherboard soundcards will handle the width and
sampling rate required. The noise is quite another issue - but
salvation may be had if the I/Q output levels are line level - the
soundcard problems for onboard soundcards are magnified when microphone
levels are mixed with digital noise.

In other words, the KX3 I/Q outputs MAY work just fine with most
soundcards - the real answers remain to be seen, and are dependent on
the particular computer soundcard you may have.

73,
Don W3FPR

On 1/9/2012 5:59 PM, David Gilbert wrote:

>
>
> Regarding sound cards for SDR use, certainly the great majority of cards
> out there would have major deficiencies ... most especially for noise,
> but also for dynamic range and sampling rate. And as you say, many
> don't even have stereo inputs. N8LP keeps a list of recommended cards
> on his web site with good information on the pros and cons of each.
>
> 73,
> Dave AB7E
>
>

Jim Brown-10

Re: OT - sound cards

In reply to this post by Mike Reublin

On 1/9/2012 2:00 PM, Mike wrote:
> How does one bond a flaptop? Most of the Win machines I've seen have a plastic case.
> My Macbook Pro has a metal case, but the screws that hold the bottom cover are tiny.

See the tutorial.

73, Jim
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K7TV

OT - sound cards

In reply to this post by K7TV

Dave,

Please understand that my audio recording need has nothing to do with my K3
or with ham radio. The USB/RS232 line connecting the computer with the K3 is
there, but the K3 is powered down. And I have no bonding between the chassis
of the two. I never had a problem, but then I never tried to record radio
output on the computer, and I never tried to feed a computer voice recording
to the K3. I have done some PSK, using a previous desktop computer as well
as the old laptop, but then I was always using a homebuilt interface that
contains isolation transformers. Yes I know, overkill, but that interface
was built before I got the K3. I am currently not interested in doing PSK or
other digital modes again, but when I get the urge, I will probably have
purchased an external soundcard that will be better than the current
computer's motherboard-integrated audio. Just for fun, because you seem to
focus on it, I made an experiment: I disconnected the RS-232 from the
computer by unplugging its USB. Then I made a recording using a dynamic
microphone and found the same noise as before. The powered speakers were
disconnected from the computer during the recording. Still connected were
other items such as monitor, keyboard, mouse, two printers and wired
Ethernet. It would certainly be possible to test with more stuff
disconnected, but that is all I have time for right now.

When you mention twang on the audio, I assume you were recording the audio
on the computer while using the noise reduction associated with its
microphone input? That is the only condition under which I hear the twang
(and then it replaces the noise). If I turn the noise reduction off, the
twang disappears and the noise comes back.

Erik K7TV

David Gilbert wrote:

OK, now that sounds a lot like the issues I had when I first began using
pre-recorded .wav files for contesting. I got several reports of "hum",
"noise", or "whine" on my transmitted signal ... all of which went away when
I disconnected the RS-232 cable from between the computer and the K3. As I
have mentioned several times here before, it took a very short piece of
shielded braid between the chassis of the K3 and the chassis of the computer
to fix it so that I could reconnect the RS-232 cable without issues. I
started with a couple of feet of braid and had to go all the way down to
eight inches before I could no longer notice the problem.

You don't say what measures you've taken to bond the chassis of your K3 to
your computer, but that would be my first suggestion. Your symptoms sound
almost identical ... even with respect to the noise during pauses and the
metallic twang at the end of words.

Regarding sound cards for SDR use, certainly the great majority of cards out
there would have major deficiencies ... most especially for noise, but also
for dynamic range and sampling rate. And as you say, many don't even have
stereo inputs. N8LP keeps a list of recommended cards on his web site with
good information on the pros and cons of each.

73,
Dave AB7E

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