Detector signal clipping

Detector signal clipping is loss of signal information when a recorded output cannot exceed an allowed range. In mass spectrometry, a simple model for an upper recording limit $L$ is $y=\min (x,L)$, where $x$ is the otherwise linear signal and $y$ is the stored value. This can arise at an analog-to-digital converter; mass spectrometer detector saturation can also introduce nonlinear response before digitization, without necessarily producing a perfectly flat ceiling.

Consider invented, equally spaced samples $(1,3,8,3,1)$ across a peak. Clipping at $L=5$ records $(1,3,5,3,1)$, reducing the sample sum from $16$ to $13$, a loss of $18.75\%$. The much larger peak $(1,3,50,3,1)$ gives exactly the same clipped samples. No calculation on those samples alone can distinguish the two original peak heights. Integrating the clipped peak therefore underestimates the signal, and a flat top is a warning rather than a measurement of the missing height.

Additional information can sometimes support an estimate. A study of timsTOF data inferred saturated isotope intensities using an unsaturated member of the isotope pattern and a model of relative isotope abundance. The missing information then comes from the model and the additional peak, rather than from the clipped values themselves. Its reported threshold belongs to that instrument and analysis, rather than defining a universal saturation limit.^[ref]