I recommend as follows:
1/
Look at Task Manager, double click the CPU column in Processes, and report what processes are using how much CPU.
2/
Perhaps you notice the disk making more noise than usual. This could mean disk thrashing during the copy/play operations.
3/
If you don't have much RAM, then the disk could be thrashing as it pages Windows in/out.
What's your hardware?
Suspishio
My advice is at your risk
Qosmio G50-10H; T9400 2.53GHz Core 2 Duo; 4GB RAM; Vista HP (32)
nForce 680i LT; Q6600 Quad Core 2.4GHz; 8GB RAM; XP Pro (64)
Dell XPS M1710; T7200 2GHz Core 2 Duo; 2GB RAM; XP Pro (32)