We are using Garageband and getting poor quality vocals using an external mic. We are hearing the sound of comp imac g5 on mic as background noise and the signal quality in comp to instruments in gb is poor. The vocal is not even being heard, please help! Can it be overcome by using a preamp or usb hub as we need to boost vocal levels to be heard over the instruments. Any help would be greatly appreciated. Please see our additional comments below!