Before you go jamming all your microphones and noisemakers into the Pi, let's take a minute to get to know the underlying sound system and the audio capabilities of the Raspberry Pi board itself.
The Advanced Linux Sound Architecture (ALSA), is the underlying framework responsible for making all the sound stuff work on the Pi. ALSA provides kernel drivers for the Pi itself and for most USB gadgets that produce or record sound. The framework also includes code to help programmers make audio applications and a couple of command-line utilities that will prove very useful to us.
In ALSA lingo, each audio device on your system is a card, a word inherited from the days when most computers had a dedicated sound card. This means that any USB device you connect that makes or records sound is a card as far as ALSA is concerned—be it a microphone, headset, or webcam.
Type in the following command to view a list of all connected audio devices...