Hi,
Audacity does'nt loop samples, it just repeats between two marks or just copies a certain number of the sample to make a loop with certain lenght .
You must use a soft able to loop your sample as Wavosaure, Extrem Sampler Converter or any soft like these. After modification of your samples, you save them and you can use them in YEM to create voices.
Regards
Seagull29