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 on a current epoch t; - a memory comprising at least one reference covariance matrix Σ̅ t, at least one first threshold and the mean and standard deviation of Riemannian distances from the previous epochs; and - a computing unit for computing a signal quality index; wherein the memory is connected to the computing unit and the at least two sensors are connected to the computing unit; and wherein the computing unit: - selects at least a first subset of channels from said multichannel bio-signal and/or applies at least one frequency filtering to said multichannel bio-signal from said first subset in order to get at least a first selected bio-signal on the current epoch t; - selects at least a second subset of channels from said multichannel bio-signal and/or applies at least one frequency filtering to said multichannel bio-signal from said second subset in order to get at least a second selected bio-signal on the current epoch t; - for each of said at least the first and the second selected bio-signals on the current epoch t: ▪ computes a current covariance matrix Σ; ▪ computes the current Riemannian distance d between said current covariance matrix Σ and the at least one reference covariance matrix Σ̅ t; ▪ computes an intermediary index based on a normalization of the current Riemannian distance d by the mean and the standard deviation of the previous Riemannian distances obtained on the previous epochs for which the intermediary index was inferior to the first threshold; and - computes a signal quality index based at least on the intermediary index for each of said at least two selected bio-signals. - at least two sensors for acquiring one multichannel bio-signal of said subject on a current epoch t; - a memory comprising at least one reference covariance matrix Σ̅ t, at least one first threshold and the mean and standard deviation of Riemannian distances from the previous epochs; and - a computing unit for computing a signal quality index; - selects at least a first subset of channels from said multichannel bio-signal and/or applies at least one frequency filtering to said multichannel bio-signal from said first subset in order to get at least a first selected bio-signal on the current epoch t; - selects at least a second subset of channels from said multichannel bio-signal and/or applies at least one frequency filtering to said multichannel bio-signal from said second subset in order to get at least a second selected bio-signal on the current epoch t; - for each of said at least the first and the second selected bio-signals on the current epoch t: ▪ computes a current covariance matrix Σ; ▪ computes the current Riemannian distance d between said current covariance matrix Σ and the at least one reference covariance matrix Σ̅ t; ▪ computes an intermediary index based on a normalization of the current Riemannian distance d by the mean and the standard deviation of the previous Riemannian distances obtained on the previous epochs for which the intermediary index was inferior to the first threshold; and ▪ computes a current covariance matrix Σ; ▪ computes the current Riemannian distance d between said current covariance matrix Σ and the at least one reference covariance matrix Σ̅ t; ▪ computes an intermediary index based on a normalization of the current Riemannian distance d by the mean and the standard deviation of the previous Riemannian distances obtained on the previous epochs for which the intermediary index was inferior to the first threshold; and - computes a signal quality index based at least on the intermediary index for each of said at least two selected bio-signals.