As with all audio recording the final result is only as good as the original source file. Adding extra noise to a RealAudio file can be even worse since it takes up extra bandwidth. If possible you should try to record your original source files in a professional studio and get them as 16-bit WAV files for conversion to RealAudio. In reality, not everyone has a recording studio. Even if you are just recording at your computer using a microphone and a sound card there are things you can do to improve sound quality.
Professionals know that the best end product comes from a good source file.
Try to avoid recording from consumer grade tapes such as Type 1 VCR tape or cheap audio tape. At Discovery we've tried to encode taped phone interviews that have turned out very poorly. Buy good equipment. Make sure the microphone is a professional one, not the one included with your computer. Make sure the sound card is capable of 16bit recording at 44MHz or 48Mhz.