A transformer is an electrical device that allows an AC input signal (like audio) to produce a related AC output signal without the input and output being physically connected together. ... By changing the number of wire turns in each winding, transformers can be manufactured to have various impedance ratios. An audio signal is a representation of sound, typically as an electrical voltage for analog signals and a binary number for digital signals. Transformers and Audio Signal are available at Jotrin Electronics.