The partial pressure will not affect the waveform, and low-pass filtering is the chief culprit of waveform change. It may not be a standard triangular wave after filtering. Depending on the cut-off frequency and filtering effect of your filter, excellent filtering effect can filter out beautiful sine waves.

From the spectrum, the square wave is composed of 1, 2, 3, 4, etc. A square wave with a duty cycle of 50% consists of 1.