  In the black hole perturbation theory framework, two different physical
pictures for echoes in compact objects have been proposed. The first mechanism
interprets echoes as repeated reflections of gravitational waves within a
potential well, where the echo period is defined by twice the distance related
to the spatial displacement operator that separates two local maxima of the
effective potential. The second mechanism associates echoes with a
discontinuity in the effective potential, potentially associated with specific
accretion processes, without necessarily introducing a second local maximum in
the effective potential. This discontinuity leads to echo signals that are
typically attenuated over time more quickly, with their period dictated by the
characteristics of the transfer amplitudes. In both scenarios, the echoes
correspond to a new category of quasinormal modes with minor real parts, with
their period connected to the spacing between successive modes in the frequency
domain. This work elaborates on a unified framework in compact stars that
encompasses both echo mechanisms. It suggests that these two types of echoes
derive from different physical origins and can be independently triggered. The
occurrence and interplay between these two types of echoes are demonstrated
through numerical simulations. %The observational relevance of this study is
also addressed.
