Instructions
Computer Microphone
Connect a USB or headphone jack microphone to your computer.
Click on the "Start" menu and scroll to "Control Panel." Double-click on the "Sound" icon.
Press the "Recording" tab and locate the icon of your microphone. Highlight the microphone and click on the "Set as Default" button. Press "Apply," then "OK."
Open your Nintendo DS emulator and navigate to the portion of the game where you blow into the microphone.
Speak into the microphone. Typically, a computer microphone requires a louder input than the DS microphone.
Audacity
Visit the Audacity website and click on the "Download" button.
Install Audacity by following the instructions that appear at the installation prompt. Double-click on the "Audacity" icon to launch the program.
Open the "Sound" menu and scroll to "Stereo Mix." This adjusts your computer so that it recognizes output as input.
Open your Nintendo DS emulator and navigate to the portion of the game where you blow into the microphone.
Launch a media player such as iTunes, VLC or Windows Media Player. Double-click on a song or video file to play it. The DS emulator recognizes this sound as microphone input.