The more fluctuations, the higher the frequency. Higher frequency translates into higher notes. Low frequency produces low, deep notes. The signal also fluctuates in loudness. This loudness is called amplitude.
Low volume is low amplitude.
Digital Signals Digital signals are signals that are transferred as numbers. They are transferred using binary, so all that is on the recording medium are 1s and 0s. In digital communications the only values ever recorded are 1s or 0s. There are no in-between values, and thus, there is no amplitude. As all data are transferred at the same rate, no frequency occurs.