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 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
