If your digital audio project draws on a number of audio components for sound audio, then you will benefit from adding a small mixer, a scaled-down version of the large mixing boards seen in recording studios. A mixer allows you to switch smoothly between multiple input sources without removing and replacing cables. An amplifier can provide the same functionality, but typically an amplifier can accommodate no more than three or four input sources. A eight-input or sixteen-input mixer should fill the needs of most digital audio projects.
Each input of a basic mixer has jacks to receive the input signal and a dial or slider called a potentiometer (or ``pot''). The pot is used to control the volume of each input and allows the user to fade a source in or out. For example, if you typically include a spoken announcement or description at the beginning of an audio-reserve selection, the mixer's potentiometers will allow you to make a seamless transition from the announcement to the music by turning down the volume of the microphone after the announcement while turning up the volume of the turntable or other audio component. More sophisticated mixers have input sensitivity controls, filters, equalizers, and other features.
A mixer also provides multiple outputs. One output will be routed to your computer's soundcard or audio interface. You may choose to have another output routed to an amplifier equipped with speakers so that you can cue up sound recordings and play back the audio you have created on something other than the small speakers supplied with most computers. Mixers also have a headphone jack so that you can monitor exactly what is being output by the mixer.