Another notable issue is the sampling frequency and the associated change in the low‐pass hardware filter. These filters are implemented with specific hardware (rather than the digital filtering applied in the postacquisition data cleaning phase) and are required to avoid so‐called aliasing effects in the analog‐to‐digital conversion phase where high‐frequency oscillations can be mistaken for low‐frequency oscillations. Unfortunately, these anti‐aliasing hardware filters also affect the oscillatory amplitude and phase of oscillations near the filter boundary, which is set in relation to the sampling frequency. When the sampling rate is too low (e.g., 256 Hz with an anti‐aliasing filter at 64 Hz), this will affect EEG power well below the 64 Hz cutoff frequency. Moreover, causal filters substantially affect the phase of oscillations, which will subsequently affect cross‐frequency amplitude–phase coupling and phase‐locking values. These issues are easily avoided by increasing sampling frequency and the causal low‐pass filter settings.
