Fourier power spectral density averaged over 59 single pulses that exhibit extensive quasi-periodic microstructure in the PC profile component. The black solid line shows the sample mean, and the grey shaded area its standard error for the combined PC and MP on-pulse phase range. The black dotted line is the same for the off-pulse region. The grey dashed lines mark significant features. The dominant feature occurs near 1200 Hz or 0.83 ms.