The present invention relates to a system for computing a signal quality index from a multichannel bio-signal of a subject, said system comprising at least two sensors for acquiring one multichannel bio-signal of said subject; a memory comprising a reference covariance matrix and; a computing unit for computing a signal quality index, wherein the computing unit computes Riemannian distances between the reference covariance matrix and covariance matrices obtained from the multichannel bio-signal.