Many wireless systems use a process called companding that compresses the transmitted audio signal at the microphone then expands it at the receiver to restore the dynamic range of the audio. This is done to deal with the limited capacity of wireless channels. Other circuitry is used to detect and remove noise from the transmitted signal. Because systems from different manufacturers, or even different systems from the same manufacturer, have different methods of companding, you should avoid mixing components from different systems, even if they use the same frequency. Unpredictable results can occur.
Digital wireless systems convert the audio signal captured by the microphone into a digital bitstream at the transmitter then convert the bitstream to an audio signal at the receiver. The main advantage is elimination of the need for companding and the signal degradation such processing can cause. Since the receiver only processes digital ones and zeroes, radio-frequency interference is not a factor. That said, the best high-end analog wireless systems can rival digital systems in terms of their dynamic range and resistance to interference.
Digital technology assures perfect transmission of vocal or instrument signals.