The PCI card I'm working with was made to receive the signal as a 32 bits frame (16 bits by channels) each time I write to the file device so I have to turn the src_data.data_out frames (2 floats) into a unique 32bit unsigned long and write it: 1) "unsigned long frame;" : I declare an unsigned long that will receive the entire frame. 2) "frame = (unsigned long) ((src_data.data_out[sent]))>>16;" : I convert the float at the index equal to sent and initialise the frame with it. So my frame look like this 0000000000000000XXXXXXXXXXXXXXXX Where Xs represent one channel signal. 3) "frame |= (((unsigned long) (src_data.data_out[sent+1])) & 0xFFFF0000);" Apply a mask to the 16 first low bits of the data_out float value and aplly a OR between it and frame. It should look like this : yyyyyyyyyyyyyyyy0000000000000000 | 0000000000000000XXXXXXXXXXXXXXXX = YYYYYYYYYYYYYYYYXXXXXXXXXXXX Where Ys is the other channel signal. Is it clear enough,I hope so :) I have to emphasize that this stuff seems to work because when I send the src_data.data_in frames buffer this way, the signal is perfect.