  We report on simultaneous wideband observations of Crab giant pulses with the
Parkes radio telescope and the Murchison Widefield Array (MWA). The
observations were conducted simultaneously at 732 and 3100 MHz with Parkes, and
at 120.96, 165.76 and 210.56 MHz with the MWA. Flux density calibration of the
MWA data was accomplished using a novel technique based on tied-array beam
simulations. We detected between 90-648 giant pulses in the 120.96-210.56 MHz
MWA subbands above a $ 5.5\sigma $ threshold while in the Parkes subbands we
detected 6344 and 231 giant pulses above a threshold of $ 6\sigma $ at 732 and
3100 MHz, respectively. We show, for the first time over a wide frequency
range, that the average spectrum of Crab giant pulses exhibits a significant
flattening at low frequencies. The spectral index, $ \alpha $, for giant pulses
evolves from a steep, narrow distribution with a mean $ \alpha=-2.6 $ and width
$\sigma_\alpha=0.5 $ between 732 and 3100 MHz, to a wide, flat distribution of
spectral indices with a mean $ \alpha=-0.7 $ and width $ \sigma_\alpha=1.4 $
between 120.96 and 165.76 MHz. We also comment on the plausibility of giant
pulse models for Fast Radio Bursts based on this spectral information.
