Unit of nn_intervals

[GanshengT]

Hi,

After encountering an UserWarning form spicy.signal.spectral (UserWarning: nperseg = 256 is greater than input length = 5, using nperseg = 5), I check the code and it seems that the function get_frequency_domain_features only takes nn_intervals in ms.

Please run the following script to replicate the results:

from hrvanalysis import get_frequency_domain_features
import pyhrv.frequency_domain as fd. # used as a reference

nn_intervals_in_s = np.random.uniform(0.4,1.8, size=(2000,))
print('frequency domain of nn_intervals in seconds')
print(get_frequency_domain_features(nn_intervals_in_s))

nn_intervals_in_ms = nn_intervals_in_s * 1000
print('frequency domain of nn_intervals in miliseconds')
print(get_frequency_domain_features(nn_intervals_in_ms))

print('frequency domain of nn_intervals in miliseconds by pyhrv')
fd.welch_psd(nn_intervals_in_ms)

print('frequency domain of nn_intervals in seconds by pyhrv')
fd.welch_psd(nn_intervals_in_s)

If this is the case, please specify the unit of nn_intervals in the documentation.