That is not quite accurate. The Arduino guarantees that 3V or higher will be recognized as high, but it reserves the right to have the actual threshhold be lower. So one device thinks high is 2.8V, another thinks it is 2.0V, another thinks it is 2.4V, etc. and yet they all meet the guarantee that if you drive a pin with 3V or higher, it will be considered "high".
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The Rugged Audio Shield: Line In, Mic In, Headphone Out, microSD socket, potentiometer, play/record WAV files