Cuts through the azimuthally averaged power spectra shown in Fig. 2 (cut along the dashed lines). Top: power at a constant frequency, ν = 3.4 mHz, bottom: power at a constant wavenumber, kR_⊙ = 466. Four configurations are shown. Thick solid black curve: no compression is applied to the data, thick dashed blue curve: the Dopplergrams are compressed using quantization (two velocity bins), solid red curve: JPEG compression (quality = 5), dashed green curve: 2 × 2 subsampling and JPEG compression with a quality of 10. The power shown is an average of twenty time-series, each of them having a length of eight hours. We normalized the bit-truncated Dopplergrams to have the same variance as the uncompressed data before computing power spectra. All compression methods slightly decrease the power of the modes and add additional noise to the power.