Good news for Dr. Scott Hardens, PhD. Sound Card ECG:

«Conclusion: On the basis of the results of the present study, we suggest that the calculation of HRV values in the time and frequency domains by RR series obtained from the PC-based sound card is probably as reliable as those obtained by the gold standard Biopac MP36.»

https://www.researchgate.net/profile/Maheshkumar-Kuppusamy/publication/305693497_Validation_of_PC-based_Sound_Card_with_Biopac_for_Digitalization_of_ECG_Recording_in_Short-term_HRV_Analysis/links/57f1d04608ae8da3ce4ec509/Validation-of-PC-based-Sound-Card-with-Biopac-for-Digitalization-of-ECG-Recording-in-Short-term-HRV-Analysis.pdf

The validators used Audacity for the Sound Card ECG, but they did as far as I know not specifiy which software they used for the Biopac MP35.

According to Scott s personal website, he is alive and kicking and programming all the time:

https://swharden.com/

That s fine, Scott. But don t forget to let go and to use your Sound Card ECG daily for letting go.