A history of mixing

Mixing is deciding how loud each part is, where it sits from left to right, how bright or warm it sounds and how much space is around it. For the first decades of recording there was no separate mixing at all: the balance happened in the room, live, while the disc was being cut. This is how it became a job, then an art, then something you do on a laptop.

The room was the mixer

In the acoustic era, the engineer balanced a band by moving people closer to or further from the horn. After 1925, with microphones and amplifiers, an engineer could use several microphones and blend them on a mixing desk (the console), but everything was still mixed live as the performance happened. If the solo was too quiet, the take was ruined.

Tape and multitrack make mixing a stage

Once parts were recorded on separate tracks of tape, the balance no longer had to be decided while the band played. The mixdown became its own session: play the multitrack tape back through the console and record the blend onto a two-track (stereo) machine. Mixing moved from capturing a performance to building one, and the engineer's choices became part of the sound of the record.

The consoles grew with the tape machines. At Abbey Road the Beatles worked on EMI's own valve desks; engineer Geoff Emerick described the one used for Sgt. Pepper as eight inputs and four outputs. In Britain, Rupert Neve built a transistor console for Philips's London studio in 1964 and went on to make the desks and channel strips (such as the 1073) that are still copied today. In 1979 Solid State Logic launched the SL 4000 E: a compressor and gate on every channel, a compressor across the whole mix (the famous "bus compressor"), and a computer that could remember settings. It defined the sound of big pop and rock mixes through the 1980s and beyond.

Space, echo and control

A lot of what we think of as "production" began as engineers trying to fake a room or tame a performance:

• Reverb. Bill Putnam is credited with the first creative use of artificial reverb on a pop record in 1947, using a reverberant room as an echo chamber. In 1957 the German company EMT made the EMT 140, a large steel plate that rang like a room and fitted in a corner; Abbey Road bought four that year. The first practical digital reverb, the EMT 250, came in 1976.
• Echo and delay came from tape: play back a recording a fraction of a second after it's recorded and you get the "slapback" on 1950s rock 'n' roll vocals.
• Compression. Compressors were built to stop broadcasts and records overloading, then engineers discovered they made things sound bigger and more exciting. Putnam's 1176 (1967), one of the first compressors built with transistors instead of valves, is still on countless vocals, mostly as a plug-in now.

Many hands on the faders

Before automation, a mix was a performance. Every fade, every vocal lift and every mute had to be done by hand as the tape played, often with the engineer, assistant, producer and band members each riding a few faders. One wrong move and you started again. In the 1970s consoles began to remember fader moves. Neve's NECAM (1977), first installed at George Martin's AIR Studios in London, was the first system with faders that moved by themselves. SSL's computer added Total Recall: it stored every knob on the desk so a mix could be set up again weeks later, although an assistant still had to turn each knob back by hand following the screen.

Mixing in the box

With Pro Tools in the 1990s and plug-ins running on the computer from 1996, the console, the effects rack and the automation all moved inside the computer, "in the box". The changes were huge:

• Recall is free. Open the session and every setting, plug-in and fader move is exactly where you left it.
• Tracks are effectively unlimited. No more bouncing to free up space.
• Every parameter can be automated, not just faders and mutes.
• Classic gear became software. Plug-in versions of the 1176, the EMT plates, Neve and SSL channels put that history in every bedroom studio.

Many professionals still mix "hybrid", with a few favourite pieces of hardware alongside the computer. But the questions mixing answers haven't changed since a band stood around a horn: can you hear every part, does the song build, and does it sound like a record?