Observation of non-reciprocal harmonic conversion in real sounds

Abstract Reciprocity guarantees that in most media, sound transmission is symmetric between two points of space when the location source and receiver are interchanged. This fundamental law can be broken non-linear often at cost detrimental input power levels, large insertion losses, ideally prepared single-frequency signals. Thus, previous observations non-reciprocal have focused on pure tones, cannot handle real sounds composed various harmonics a low-frequency note, as generated for example by musical instruments. Here, we extend reach acoustics achieving large, tunable, timbre-preserved notes several harmonics, originating from achieved non-linear, actively reconfigurable, non-Hermitian isolator arbitrarily low any audible frequency, while providing isolation levels up to 30dB tunable level gain. Our findings may find applications isolation, noise control, metamaterials, analog audio processing.