Greetings,

I'm making music on a rather old PC with an intel dual-core CPU, 4GB of DDR2 RAM and an E-MU 1212m PCI card.
It still runs pretty decent, but strange things happen with the audio. Even with a few percussion loops and a single instance of Absynth, the buffer fills up, audio starts skipping and the CPU meter goes 100% (in Live 8 and Reaper).
You might think the specs are low, but I could run pretty heavy projects with little trouble. I've tried increasing the buffer only to find out it's getting worse.

Same story with linux, playing some mp3s and running Firefox or multple other apps makes the sound skip.
What should I do?

IRQ conflict?
Try the 1212m in another PCi port or configure your system so, that the 1212m IRQ is not shared by another device.

Deactivate all cpu & system power saving features in your bios and windows.

Deactivate all devices, drivers & programs you don't need for audio.

Defrag your HD.

Check your system with "DPC Latency Checker" to find the bottleneck:
http://www.thesycon.de/eng/latency_check.shtml

Its probably not the soundcard, maybe overheating CPU? After some years, dust collects on fans/heatsinks. Fans can stop or thermal compound becomes ineffective and needs to be renewed. Could be bad connection to the soundcard/motherboard.

I used to have problems with an Audigy 2 ZS when I added RAM to my machine, any amount above 2054MB would make it impossible to play audio properly. Probably not the same issue but I still mention it because they are both Creative cards. An M-Audio Audiophile 2496 runs great on the same system with 4GB.

It's a fresh Windows installation. I initially thought there's a problem with the Windows 7 drivers, but same happens on XP.
Except for the video card, nothing has changed in the configuration. Though the video card has some audio chip built-in.
I'll try the latency checker.

I've changed ports, disabled nvidia's audio and still nothing.
I've noticed that things go bad when the computer is loading the interface. The same thing happens on Linux, I hear noises when I open apps.

http://www.murga-linux.com/puppy/viewtopic.php?t=72402

not all linux are good out of the box, try a live cd from the iso
in the first link. Use a few sounds in multitimbral zynaddsubfx to get
some cpu cycles burning. Use command top or htop to display
cpu, ram, and other resources.

Command ps ux will show this, without the live monitoring found in htop.

Does the e-mu have any jumpers that may need positioning? How about
bitrate, the card may default to other than the OS, and doing conversion is eating cpu.

In linux, cat /proc/asound/cards will mention the irq in use, to help see conflicts.
You may need to replace the video card again.

The other suggestions are good ones. As noted, the mAudio card is great for linux audio.
Cheers

I later found out that the problem was with the nvidia card. It was all about a power saving feature the drivers have, but which increases audio latency. It's a known problem, but for some reason developers ignore it. So I believe my advice is to stay away from NVIDIA cards if you're into music production.

You can't make that blanket accusation as it'll be system dependent. We ship loads of audio boxes a month running Nvidia and I can think of just one in the last year that had a inherent compability issue going on. I can trot out plenty of ATI examples too however... and matrox and... well pretty much anything.

Well it's a known issue with DPC latency, if you do a Google search you'll get plenty of results. I had none of these problems with ATI cards.

That's why I said system dependent, I've got problems with ATI Catalyst and DPC right now on a Win8 spec sat in front of me that doesn't occur when you stick an Nvidia in there. If you do a Google search for most things (including "ATI DPC problems") you'll also get a stack of results.

Whilst I appreciate it fixed it for you this time, I was just making the point that neither side is perfect and it often changes from revision to revision and a lot of problems end up coming down to multiple factors in the machine, not just the drivers latency mon points the finger at.