The mixer has been a critical part of any studio or DJ booth for decades. This is the heart of a pro audio setup; the one piece of hardware that takes all of your sound sources and puts them together into a cohesive mix. Just like any other piece of musical technology, mixers are always evolving. The "digitalization" of audio equipment gave us today's selection of digital mixers, making them more powerful and versatile than their analog ancestors could ever dream of.
If you're looking for a mixer to put in your studio, there are plenty of great choices here. To pick out the best option for you, one of the simplest ways to start is by deciding how many channels you need. A small hobby studio can get the job done with the 8 channels of the compact, easy-to-use QSC TouchMix-8. But if you're looking to power a full-scale professional recording house, then you'll be looking at bigger boards like the PreSonus StudioLive 32.4.2 AI 32-channel Digital Mixer.
There's no shortage of fantastic models for live sound and DJ use, too. One great example is the Line 6 StageScape M20d mixer, which is designed from the ground up for live sound systems. Touchscreen-based control makes the M20d a cinch to use, which is important when you're working on a live concert where there's no room for error or delays. Further to that, if you like the idea of using a touchscreen to control your mixer, then you've got to check out the Phonic Acapela16 as well as the Mackie DL1608L and DL806L. These high-tech digital mixers are actually designed to use a tablet as their control surface, putting you more in touch with the device than would ever be possible with purely physical controls.
The bottom line is this: it's the twenty-first century, and digital production is the standard. Any sound booth or studio should have a digital mixer tying everything together. With one of these, you'll get all the sound quality that analog mixers have been delivering for years, along with a huge helping of versatility on top of that.