The signal-to-noise ratio of FTIR-PAS measurements depends on the FTIR spectrometer's performance level as well as the detector sensitivity and noise level, and signal generation efficiency of the sample. Low FTIR mirror velocities produce low modulation frequencies and more efficient signal generation due to the slow thermal response of samples. Low modulation frequencies yield higher signal-to-noise spectra for a FTIR's mirror servo-control system. A high infrared beam intensity is also beneficial and requires a large source aperture, high source intensity, and low f number optics. All commercial FTIR systems provide combinations of these beneficial features to an extent that good FTIR-PAS measurements can be performed assuming that the FTIR is in good operating condition.

Mirror velocity is given in Table 2 as an optical path difference velocity, v, which allows the modulation frequency, f, at a given wavenumber, , to be calculated from the formula, . As discussed in the last section, the mirror velocity can be increased to decrease the sampling depth and vice versa. Step-scan systems allow a desired modulation frequency to be selected that is constant at all wavenumbers thus providing a constant sampling depth for values of absorbance below the onset of signal saturation.^8,11 Resolution can also be adjusted for specific needs but should not be set higher than necessary to resolve the structure of interest because as the resolution is increased, noise will also increase for a set number of scans. The spectral range is dictated by the spectrometer's source and beam splitter provided that the photoacoustic detector window has suitable transparency. In the near-infrared, visible, and ultraviolet spectral regions, very low mirror velocity and step-scan interferometers are particularly useful in order to keep modulation frequencies from becoming too high at the high wavenumbers of these spectral regions. The signal-to-noise ratio increases proportional to the square root of the number of scans, therefore the number of scans can be adjusted to provide the signal-to-noise ratio necessary for given applications.