Dell Inspiron and Latitude Sigma Tel Audio quirks?

Hi all!
I have just installed Audacity on my laptop with the intention to rip my old vinyl records to CD. Program seems to work fine but I have a couple of problems that are stopping me. I get an annoying zinging sound in the silent parts of the records. I have connected the line out from my (home build and very old) sound system that would normally go to my (also pre-historic) cassette deck directly to the microphone jac. Levels seem OK by the looks of the meter toolbars. Doesn’t seem to make any difference if I select Line in or External mic. Maybe it is just the crappy sound card in the PD (Dell Inspiron 630m), probably digital noise coupling through.

So I tought I’d test with a different laptop and borrowed amachine from work, a Dell Inspiron a few years old, but there I encounter a totally different quirk. No background noise but there seem to be some sort of muting/AGC control that kicks in. If the input level dropps, the mic and/or line input gets muted. Total silence, nothing heard in soft passages on the record. When the input level rises, the muting is released and instead the level is adjusted to a few dB below red-line, like an Automatic Gain Control. Doesn’t make for very agreable sound. There is no hint of why this ocurs, the controls for input level of the sound card shows no trace of it. Could it be some other software that has hi-jacked the audo? (I am suspecting Scype, since I have that on my work Pc but not on my private one).

Maybe all this boils down to me having to buy an external (USB) sound card, I know I can get one for about 50$, but beeing an engineer I would really like to have my curiosity satisfied and find out what is causeing this. Anyone with a clue? I tried some searches on this forum, but eiter my imagination for terms is lacking or there are no previous posts with similar context.

Thanks in advance.
P.S. Don’t know how prone to spam this forum is, so i registered with a slightly off email. Remove the obvious if you want to email me directly. D.S.

I’ve recently tested a fairly high end Toshiba laptop.
The sound quality of the on-board sound is not very good at all. There is noticeable noise with low level audio, and also noticeable “gating” when the audio level drops below a certain level. It is good enough for casual listening through computer speakers, or the built in speakers, but playing through a reasonably good sound system shows the weaknesses very clearly.

Adding a Behringer UCA 202 USB sound card provides a considerable improvement to the sound, though there is still some interference from the power supply when plugged in. This is not really noticeable when connected to a pair of powered speakers costing around $150, but sounds very bad when connected to a $6000 PA system. The power supply problem can be cured by either running from batteries, or connecting through a DI box with balanced outputs.

I have yet to find a laptop with good on-board sound.