Audio Interfaces: Mixers

by Pablo Bellinghausen

When both beginners and professionals alike picture a high-end studio, one of the first things that will come to mind is likely to be an imposing analogue mixer in the middle of the room. This, alongside their ubiquity in live PA systems, will very often lead people to believe that even small studios somehow require a mixer in a professional setup.

SSL SL4064G+ @ ONKIO HAUS 6st_DSC0906

SSL analogue desk and Pro Tools system: a familiar sight in high-end studios

To clarify, the main purpose of mixers, both analogue and digital, is to mix several channels (for example all the different mics used in a full band recording) down into a single stereo signal. They are also used to route secondary mixes to other places, such as different monitoring feeds for musicians. This is critical in a live situation, and in an analogue recording studio the mixer really is the hub that routes all the signals from the microphones to the tape machines, and back into all the headphones and speakers.

In a basic digital studio however, the mixing is done inside the computer software itself, and all the routing is done by the audio interface; mixing the signal in any way before it reaches the computer would prevent you from separating the different elements of the performance, completely defeating the purpose of multi-track recording.

Control surfaces like the Icon QCon or Avid Artist ranges of MIDI controllers, as well as touch-control screens such as the Raven MTi and MTX will allow the tactile mixer experience that many engineers prefer (as opposed to using a mouse for setting up levels), yet although they look very similar to a mixer, no audio actually goes through them; they just send volume level information via the MIDI standard to the computer; the computer is still adding up the channels internally so the mix still happens “in the box”.


Avid Artist control surfaces offer tactile control for “in the box” mixes 

Basic USB mixers like the Allen & Heath ZED-12FX are primarily live tools, with the added perk that they can send a single stereo feed straight into a computer for archiving. They don’t have the required circuitry to send all the tracks separately to the recording software, and they are not meant to.

Large digital desks will often have this capability; products like the Behringer X32 or its big brother the Midas M32 are incredibly versatile and can indeed send multi-track signals to software, apply effects, and mix down audio simultaneously, as a “jack-of-all-trades” that will perform well both live and in the studio. However, with very few exceptions, all the extra functionality will be completely redundant in a recording studio, and the money can therefore be better spent somewhere else.


The Midas M32 is great for recording, but some live-specific features will be redundant

Very high-end digital studios like the one in the top picture will often have an analogue mixer for “flavour”, meaning that engineers will run audio through it for the pleasant colouration they bring, even sending an entire multi-track project onto its separate channels to perform the mixing manually, analogue style. This is a common workflow for engineers who learned in the analogue days and want to keep that visceral feeling of moving the faders and manually crafting a mix, and of course for older facilities that already had one!

Summing mixers are a simplified version of that, meant to receive separate channels of a digitally-balanced mix to perform the final summing in the analogue realm, letting the circuitry “warm up” the sound.


The Neve 8816 summing mixer: analogue flavour for digital mixes in only 2U

Whilst it is a very common opinion in professional circles that very high quality analogue circuitry adds a special kind of sheen and organic quality to the sound that is hard to get through digital effects, it is important to stress that professional-quality analogue audio is inherently expensive, and that the classic consoles high-end studios will use (Neve, SSL and API come to mind) will cost anywhere from dozens of thousands of pounds to more than the price of a house!

Although it has not always been the case due to poor coding in some software, the digital summing algorithms that add up all the separate channels in all professional recording programs are nowadays completely clean and transparent; if there is one thing computers do well, it’s adding things up. There used to be differences in noise floor and truncation distortion levels when performing level changes in old software because of their lack of bit-depth resolution; nowadays all major DAWs will sum audio in 32-bit floating point at the very least, which is a much higher resolution than the best analogue devices. There is a lot of misinformation floating around on the internet on this subject, but it mainly rests on ignorance about how digital audio works.

The controversy currently lies in whether high-end analogue mixing sounds subjectively better than its digital counterpart (the classic “in-the-box” vs. “out-of-the-box” argument), and this is still a valid conversation to have. In any case, the audio community agrees that in most cases budget analogue equipment will tend to deteriorate a digital signal instead of enhancing it.

In conclusion, in most project studios the workflow will require a standard audio interface, and a built-in mixer would be redundant, particularly anything that could be considered “budget”. If you’re thinking of adding some “analogue flavour” to your setup, high-quality channel strips, bus compressors, distortion units and/or valve microphones will usually be far better options.


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