Can I measure Delta waves (0-4Hz) with Emotiv hardware?
Delta waves (0-4Hz) are hard to measure accurately for several reasons.
- Typical ocular artefacts, movement artefacts, heart rate, respiration, blinks and body potential drift also have strong components at low frequencies. Sleep studies measure delta frequency pretty well because the subject barely moves, is usually connected to a ground lead and has their eyes closed.
- Accurate measurement of any frequency component with FFT relies on having at least 10 cycles of the lowest frequency of interest in the sample, and assumes it is “stationary”. For 0.5Hz this is at least a 20 sec sample. FFT will round or fill to a power of 2, so 16 sec is a little short for 0.5Hz, 32sec is ideal…
- Because FFT needs many cycles to accurately estimate amplitude and phase at a frequency, low frequencies are poorly estimated – and the accuracy decreases as the frequency goes down. The power at frequency f is overestimated by a factor related to 1/f.
We don’t output delta wave power because it’s misleading. If you need it, you will need to apply corrections and maybe a different method than FFT, after removing artefacts.