What is the optimum bitrate to record human voice in normal audible quality

i am using a voice recorder to let users record their own voice. Now i want to know what is the bit-rate to record human voice in normal audible quality. I am not looking for very high quality. Recording will be done only through microphone or in built voice recorders in laptops. also what will be the streaming rate to record the voice. does it depend on users internet speed or my server speed. How to calculate the bandwidth?