text: The Post Production Audio Guide (Part Two): Sound Mixing – wolfcrow
  In Part One we looked at Sound Editing – from plain recordings to stems – the process of selecting the right tracks, cleaning them, placing them in the right position and syncing them, etc.
  In this part we'll look at the second and final stage of audio post production – Sound Mixing.
  In Part One we stopped at stems, which are premixes derived from a multitude of tracks. On large projects, these premixes are created in the sound mixing stage, rather than by the sound editors. But, what is this 'mixing'?
  Mixing is the art of:
  Adjusting levels (volume) of different tracks so they play well together.
  Finding the right balance for various channels.
  Adding, manipulating or removing certain effects and filters to change the quality of the sound.
  Preparing a final master from which other soundtracks can be derived.
  In essence, mixing is the mixing of tracks to make them play well together, while preserving the artistic intent of the filmmaker and the story. Other than this, anything goes.
  As far as filmmaking is concerned, the process is also called Re-recording.
  You need what is called a mixer. There are two fundamental types of mixers:
  Analog – the long mixing consoles that you see, like in the image above
  Digital – DAW, which might be just one computer screen, looking like analog consoles
  Today, you might find both in equal measure in the industry. What the future holds, nobody knows.
  On a large feature, each stem will have its own console, operated by one person. On low-budget productions, there's only one mixer for everything. Some mixers specialize in music or effects. On large productions, you can have two or more mixers working in tandem, each responsible for one stem.
  The captain of the ship is the Lead Mixer, sometimes called the re-recording mixer.
  What do you do in a Mix?
  There are infinite tools available at a mixer's disposal, only limited by budget. On average, the better a tool is, the more it costs. One must also factor in warranty and service. You can't halt a mixing session for want of one potentiometer (pot).
  Consider the following list a basic primer only. Here are some important functions of a mixing tool(s):
  Levels – adjusting the volume
  Muting single tracks or stems – ability to listen to only certain sections at a time
  Limiting – the power to set upper and lower limits to levels
  Compression – the ability to compress audio levels into a smaller region (reducing its dynamic range) to save space
  Expansion – the ability to increase the dynamic range, levels-wise, if you want to go that route
  Equalization – playing with the frequencies or bands of frequencies (like bass, treble, etc.)
  Filtering – taking out parts (frequencies) of sounds by passing them through filters
  Reverberation – adding reverb or echo to match sounds or generate an effect
  Pitch – change pitch
  Synthesis – generate sounds to use quickly – you can't always go back to sound editing, so some overlapping is designed into the process
  Panning – Controlling space to make sound come alive within several channels (like stereo, surround, etc.)
  These tools are not used in the order I have written them in. Sound mixers work in reels or sequences, but the workflow is always circular. The filmmakers might always change their minds, and the mixers are trained to accept these changes. That's why they charge by the hour!
  All said and done, sound mixing is a creative pursuit. Most filmmakers cannot sit through a mixing session without losing their ability to judge. Imagine the skill a sound mixer must have, then!
  What do you get at the end? You get the final mix, also called a master. But, how many masters are there?
  If you glance through the available digital audio standards for theatrical distribution, you might come across the following names:
  THX – controlled environment standard – you mix in THX-certified environment and playback in one – there is no licensing involved.
  Dolby Digital – a 6-channel encoding format – you must buy a license to use this format.
  DTS – a 6-channel encoding format – you must buy a license to use this format.
  SDDS – an 8-channel encoding format – you must buy a license to use this format.
  And many others. What do they mean?
  These are standards that attempt to keep the audio sound acceptably the same, as long as you use their equipment. In effect, what they are doing is forcing you to pay for equipment that only supports their standard, which then restricts your audio to their standard, so your audio can only play back properly in their equipment! Do you feel like you've been hit by a truck? You're not alone. To be fair to them, though, this is a necessary evil. Otherwise, your audio will sound differently in every venue. What's the point of preserving your artistic intention so carefully, if nobody else is going to hear it?
  Also, these guys have pretty good 'standards', and they are industry leaders in the field of theatrical audio. The problem though, is in choosing which one is right for your project. You don't know this until you have your distribution deals in place. Otherwise, you are just shooting in the dark. A final mix keeps music and effects (M&E) separate, so that foreign language dialogues can be dubbed (another stem) instead. All tracks, stems and project files are preserved for posterity.
  From the master one proceeds to produce other mixes, like the DVD or Blu-ray mix, television stereo and 5.1 mix, etc. Unlike video transcoding, mixing must be done from scratch – it's not an automated process. It is for this reason that film audio budgets are large, and those who don't consider them in advance find themselves scratching their heads later. If your intention is a theatrical release, you must factor in all these mixes as part of your budget. Some distributors don't accept movies without M&E done separately.
  I hope this brief overview has given you enough information to get started on planning your own post production audio workflow. The road to a great soundtrack isn't an easy or linear one. Still, it needs adequate attention, and great skill from those who work on it.
  Don't ever underestimate audio.
  ← The Post Production Audio Guide (Part One): Sound Editing → Understanding the limits of Data Rates and Transmission