  We compare recent one-loop-level, scattering-amplitude-based, computations of
the classical part of the gravitational bremsstrahlung waveform to the
frequency-domain version of the corresponding
  Multipolar-Post-Minkowskian waveform result. When referring the one-loop
result to the classical averaged momenta $\bar p_a = \frac12 (p_a+p'_a)$, the
two waveforms are found to agree at the Newtonian and first post-Newtonian
levels, as well as at the first-and-a-half post-Newtonian level, i.e. for the
leading-order quadrupolar tail. However, we find that there are significant
differences at the second-and-a-half post-Newtonian level, $O\left(
\frac{G^2}{c^5} \right)$, i.e. when reaching: (i) the first post-Newtonian
correction to the linear quadrupole tail; (ii) Newtonian-level linear tails of
higher multipolarity (odd octupole and even hexadecapole); (iii)
radiation-reaction effects on the worldlines; and (iv) various contributions of
cubically nonlinear origin (notably linked to the quadrupole$\times$
quadrupole$\times$ quadrupole coupling in the wavezone). These differences are
reflected at the sub-sub-sub-leading level in the soft expansion, $ \sim \omega
\ln \omega $, i.e. $O\left(\frac{1}{t^2} \right)$ in the time domain. Finally,
we computed the first four terms of the low-frequency expansion of the
Multipolar-Post-Minkowskian waveform and checked that they agree with the
corresponding existing classical soft graviton results.
