I just read the specs of this particular WM8805 I2S To Coaxial SPDIF board and it says: "...Default I2S 4 lines (BCLK, LRCK, DATA, MCLK), support Raspberry, Bluetooth, etc. without master clock MCLK output 3 lines BCLK, LRCK, DATA. MCLK is provided by the crystal clock on the board by default...