I did some more research into the “meh” quality of the Stinkpad onboard audio, and it turned out that the sound chip resamples everything internally to 48kHz. The resampling doesn’t seem to cause any bad artifacts, just a slight loss of treble through the anti-alias filter, but that very lack of high end is probably what makes it meh.
So I decided to have one last attempt at getting an audiophile-grade output from old Stinkpad, and if it failed I would throw him out of the window and make do with a single computer. I’ve long been a fan of M-Audio products: I struggled with music production on consumer soundcards for years, until the day I bought a Delta 66, and everything just worked. So I bought a Transit, which is their cheapest, lowest-channel-count USB audio doofer.
Upon installing it to the Stinkpad I got exactly the same snaps and pops as before, at the rate of about 5 per second 🙁 But this time, I noticed that they only happened when the CPU was idle, and loading it up with Winamp’s visualisation thing made them go away. There were no pops from Sound Forge, and indeed I was able to get a bit-for-bit digital copy through the Transit’s optical I/O to my MP3 player and back. (I have an IHP-120 running Rockbox that has digital I/O and can record and playback uncompressed, so I could test everything by dubbing a test file from the laptop to the IHP-120 and back, and subtracting the result from the original.)
This was a promising result that made it worth investigating more. I assumed that the problem was due to some sort of power management system that was shutting the CPU off when it was idle, and maybe taking a bit too long to power it up again, so that the USB audio stream ran dry. And now the heartwarming bit, the Thinkpad 600X might be 10 years old, but IBM/Lenovo still support it! I was able to download a power management driver compatible with XP from their site. This added a tab to XP’s Power Properties dialog, with options to disable CPU and PCI bus power management. I disabled the CPU power management, and the audio troubles were utterly gone, with the machine running considerably faster as a bonus.
Of course, in computing you never fix one problem without introducing three new ones. The CPU fan now runs full speed all the time, and I expect the battery will now last about 5 minutes while the laptop will get hot enough to fry eggs 🙁 There doesn’t seem to be any way of having this CPU power management “On for battery power but off for AC”, either. Maybe there was a driver to make that happen in Windows 98, but it wouldn’t work in XP.
Oh well, I guess this is what I get for bringing a vintage tractor on the information superhighway.