The support forum at Tunebite says that for full 4x realtime re-recording you need a 1400 MHz processor. However, I have a 600mhz machine and I have now recorded about a dozen audio lectures at 4x realtime to the .wma format with no problems. Of course, it could be because I’m using such low quality settings at 64kbps stereo which might not need a high powered processor.
If you are trying a conversion with very low quality settings, then of course you can do it 4x. Just try to make a conversion to .ogg for example with VBR. Don’t wanna be mean, but I hope your machine will survive