But now I have a different problem that I've been trying to debug: I realized that in certain workloads, the SB16 causes VERY lo […]
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But now I have a different problem that I've been trying to debug: I realized that in certain workloads, the SB16 causes VERY loud noises - pops/clicks (with headphones, they can sometimes scare the bejesus out of you).
A few instances where these clicks and pops are always occuring:
- right after MS DOS loads, during the HIMEM extended memory test.
- during 3DBench 1.0C (but much less pronounced compared to the HIMEM test)
- in certain games like Duke Nukem 3D (more rare, but once the pops occur they can be VERY loud).
The pops during the HIMEM testing were a clue, it meant that they are somehow linked to memory. So I tested every possible combination of memory timings / wait states that I could think of, but nothing worked... With the slowest timings and highest wait states the CPU performance drops to DX2-66 levels, but the SB16 noises are still there.
Through trial & error, I eventually I disabled the "memory hidden refresh" option in the BIOS and... the pops completely disappeared. If I enable it back, the noises return. So it's 100% consistently reproducible.
Unfortunately, if I disable hidden refresh, the system is very unstable (it usually freezes within the first 5 - 10 minutes after boot). Tried also toggling slow refresh together with hidden refresh, but the system either remains unstable (with hidden refresh disabled / slow refresh enabled) or with noises (hidden refresh enabled / slow refresh enabled or disabled).
Other things I've tried:
- 3 x SB16 cards (1 x CT2230 / 2 x CT2290), they all exhibit the same issue. Obviously, they work fine on some other motherboards/platforms.
- an ESS AudioDrive ES688 with Yamaha OPL3 (non-PnP) and an ESS AudioDrive ES1688 (non-PnP) - both work perfectly, no clicks and pops.
- an AWE32 CT3980 with Yamaha OPL3 (PnP) - works perfectly, no noises whatsoever (and to my ear it even sounds better than the SB16 cards)
- various 72 pin FPM memory modules (2 x 16 MB, 2 x 4 MB, etc) from multiple manufacturers - no changes with the SB16.
- temporarily switched from VLB I/O & VLB VGA to ISA I/O and ISA VGA, just to make sure that there isn't some weird VLB related quirk at play. Noises are still present, though.
Right now I'm all out of ideas. Seems that this motherboard just hates SB16s but probably works great with any other sound card 😀. Of course, I could use the AWE32 (which would be more period correct for this PC + it's better in every way), but I have other plans for that card...