Comparison of added (blue) and subtracted (red) FFRs in response to a stimulus that consists of noise shaped by the ‘da’ envelope (black, top time domain, bottom frequency domain). Because the carrier is noise, there are no resolvable frequencies contained within the stimulus. The only spectral information can be extracted from the envelope. Therefore, the FFR to this stimulus is only an envelope response, no temporal fine structure is encoded. This demonstrates that the added response is an envelope response that consists of both the fundamental frequency (100 Hz in this case) and its lower harmonics, in this case, up to ~500 Hz. When there is no spectral energy in the stimulus, there is no subtracted response.