The Audio extension features an Audio Codec IC that allows to receive and output analog audio data. This allows you to e.g. make your own audio mixer, synthesizer or program a voice recognition. Like for image processing, you also profit from FPGAs with audio processing.
The VHDPlus Audio Extension features a MAX9867 Audio Codec with 2 18bit, 48kHz ADCs and DACs. On the top you can connect a headset with stereo audio and a microphone. The connector on the bottom has stereo audio inputs and outputs. As audio input there is the choice between standard audio inputs and microphone inputs.