SONChanBytes

  SONCHANBYTES returns the number of bytes written, or buffered, on the 
  specified channel
  BYTES=SONCHANBYTES(FH, CHAN)
                      FH SON file handle
                      CHAN Channel number 0 to SONMAXCHANS-1


  Author:Malcolm Lidierth
  Matlab SON library:
  Copyright © The Author & King's College London 2005-2006