[Elecraft] OT - sound cards

[Erik Basilier]

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