The read variability of redox based resistive random access memory is one of the key characteristics with regard to its application in both data storage and novel computation in memory or neuromorphic architectures. While intrinsic noise limits the number of distinguishable states, it may be beneficial for probabilistic computing or to prevent overfitting. Thus, application and material system need to be carefully matched according to their read noise characteristics. Preceding density functional theory simulations suggested dividing oxides used in valence change memory into two categories based on the dominating conduction mechanism. We provide a comprehensive experimental study, which confirms the simulations and demonstrates how the conduction mechanism affects the variability. We analyze the signal-to-noise ratio (SNR) of five different switching oxides, revealing that oxides with shallow defect states (type 1) show high SNR whereas oxides with deep defect states (type 2) exhibit pronounced ionic noise. Thus, our results provide valuable input toward tuning of read noise characteristics by material design.