Recent developments in the coherent manipulation of electrons in ballistic conductors include the generation of time-periodic electrical currents involving one to few electronic excitations per period. However, using individual electrons as carrier of quantum information for flying qubit computation or quantum metrology applications calls for a general method to unravel the single-particle excitations embedded in a quantum electrical current and how quantum information is encoded within it. Here, we propose a general signal processing algorithm to extract the elementary single-particle states, called electronic atoms of signal, present in any periodic quantum electrical current. These excitations and their mutual quantum coherence describe the excess single-electron coherence in the same way musical notes and score describe a sound signal emitted by a music instrument. This method, which is the first step towards the development of signal processing of quantum electrical currents is illustrated by assessing the quality of experimentally relevant single electron sources. The example of randomized quantum electrical currents obtained by regularly clocked but randomly injected unit charge Lorentzian voltage pulses enables us to discuss how interplay of the coherence of the applied voltage and of the Pauli principle alter the quantum coherence between the emitted single particle excitations.