Cochlear synaptopathy — i.e. damage to the synapses connecting inner hair cells to auditory nerve fibers, driven by aging or noise exposure — is thought to be an important factor contributing to speech-in-noise (SPiN) understanding difficulties in humans. Yet, it remains unclear which non-invasive biomarkers could be used to assess this pathology. Because of its crucial role for SPiN understanding, we reasoned that addressing temporal fine-structure (TFS) coding fidelity should provide a direct estimate of the impact of synaptopathy on SPiN perception deficits. In this talk, I will present recent psychophysical and electrophysiological measurements based on complex harmonic stimuli with different spectral shapes specifically designed to reflect TFS coding fidelity. We will discuss how several markers extracted from these measurements can account for SPiN intelligibility differences measured within and across various groups of listeners, young/older, with/without outer-hair cell damage.