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Previous studies have demonstrated that structures such as a canopy or finlets placed within a boundary layer over an aerodynamic surface can attenuate pressure fluctuations on the surface without compromising aerodynamic performance. This paper describes research into the fundamental mechanisms of this pressure shielding. Experiments and analysis are performed on elemental canopy configurations (parallel arrays of streamwise rods) that eliminate the confounding effects of a leading-edge support structure. Experiments show that such a canopy produces attenuation in two distinct frequency ranges. At low frequencies (convective scales much greater than the canopy height) attenuation spectra scale on the canopy height Strouhal number, but at high frequencies (canopy scales of the order of the height) a dissipation type frequency scaling appears more appropriate. RANS calculations are performed simulating the canopy geometry directly and as a porous layer. Pressure fluctuation spectra predicted from the RANS results by separately accounting for inner and outer layer contributions are able to accurately recreate the wall pressure spectra both with and without the canopy and thus the major features of the attenuation spectra.