* Have you selected the correct CS pin for your SD-card? Uncomment the line <pre>// SdPlay.setSDCSPin(10);</pre> in the examples and enter correct pin number here.
* Your SD shield may be crap and SD communication is only possible with limited speed. Try commenting the line <pre>SPSR |= (1 << SPI2X);</pre> in function ''SD_L0_SpiSetHighSpeed()''. If this doesn't help, comment out also the first line and try again. If then init works you have a bad SD card shield.
== How to use 16-Bit audio? ==
If you want to use 16-Bit audio, you need 2 PWM outputs joined together with a resistor (see above). Select SSDA_MODE_STEREO if you want one 16-Bit output channel, select SSDA_MODE_QUAD if you want two 16-Bit output channels (works only on Mega-Arduinos or with Timer2 patch).