Amplitude Modulation mp3 input is in matrix and my system is sample based

I want to input an mp3 file as a message and modulate it with a carrier. Then pass that passband modulated signal to the AWGN. But that is not working. The error displayed is "Error in port widths or dimensions. Output port 1 of 'Simscape/AWGN Channel/In1' is a [*1024x2*] matrix." My receiver is built using Simscape, an envelope detector.