Uh... I think some you guys have no clue how digital audio recording/playback works.
When a digital recorder records something, it uses a process known as "sampling" - that is, for a 44100 sample/second recording, it takes a "snapshot" of the input every 1/44100 second. When played back by taking those samples and sending them through a DAC(digital to analog converter), you then hear it as sound if you've got a speaker plugged in.

This means that /frequency doesn't matter/. At least, not to the recorder itself. The microphone and speakers may not he able to handle high/low frequencies, but the digital hardware can.

Now, the above is only true for uncompressed .wav files. Compression - like mp3 - may easily mangle stuff that's deemed "outside of human hearing" to save space, at least at low bit rates. So, you're just going to have to experiment.