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Mixing Sound for Film - Audio Post

Often, in our own research or work we come across some great blog posts, resources or articles that we think would be worthy of sharing. Especially if they provide real world and applicable knowledge. In this case, we wanted to share a blog post by John Eye from Beach House Studios regarding mixing sound for film and TV.

John gives a great overview on some important things to consider if you are an audio post production professional or learning to be one. Take a look!

The Basics You Should Know Before You Start.

So you’re going to mix sound for film for the first time. You have been an audio engineer for a while. You have spent the years building up your skills, and you love movies! You think to yourself “mixing sound for film seems like a perfect fit”. If those previous statements are true, then it probably is a perfect fit, but there are a few differences between audio post production for film and mixing a record for commercial release.

If you have worked with other people on projects like this before, you may know most or all of the things I will cover in this article, but if you are setting out on your own for the first time, these are the key points which I found incredibly helpful to know.

Depending on the experience of the director, producer, picture editor, and most definitely the “on location” sound person, your job can vary a bit in its scope. Just know this, mixing music for bands is going to seem a lot easier after you get done mixing sound for film.

Project Timeline (Scoping)

You’ve been mixing three to five minute songs for most of your career, and you know how many hours can go into tracking and mixing a fully polished song. How in the world are you going to scope out how long it will take to mix a whole movie? I should warn you here, you are most likely going to be doing a lot more than just mixing. Think dialog clean up, audio restoration, Foley and sound effect design, as well as automated dialog replacement or ADR work.

Most small budget indie films run around the 30 minute mark, so we will use that as a measure to base your estimate on. I just finished mixing audio and all the other post production elements for a 38 minute film. I put 150 hours into that project, and that was rushing it. There was so much more that I would have loved to have done for the audio mix, but we were on a serious deadline. I think that film could have benefited from another 150 hours of work, but we didn’t have that amount of time.

I would scope out a mixing project in this way:

For a 30 minute film you will put in between 150 and 300 hours of work depending on the quality of the audio you are given. This particular film I was working on had MAJOR audio problems, so if you are handed pristine quality audio to work with, you may be able to cut that timeline down to perhaps 100-120 hours. Better to give yourself the buffer though. Always under promise and over deliver. If your film is an hour in length, just double the time to 300-600 hours. Now of course this is for pushing-it-through, low-budget films. If your director has the budget, the vision, and the desire, you may end up working for much longer. Keep in mind that Star Wars spent a whole year on audio post production. If you want that level of quality, it will take that amount of time.

Remind your director and producer in the beginning of the project that they can “have it quick, have it cheap, or have it done right. Pick only two”.

What Format?

Be sure to tell your picture editor what file formats you will need. Most likely .mov for picture lock, and an OMF or AAF session export from their editing software. If you can import an OMF or AAF file into your DAW this will save you from having to checkerboard the dialog yourself, and save a ton of time.

There is a great session format translator that can help to convert many editing session formats into compatible formats for many DAWs called AATranslator. They have a list of what formats they support, and they are very responsive if you have questions. Generally Pro Tools will import OMF and AAF files from Avid Media Composer (AMC) really well, and Logic Pro will take imports from Final Cut, and some from AMC. If your editor works in AMC and you don’t have Pro Tools, you can do either one of two things. One, get them to export from AMC into Pro Tools, and then export an OMF or AAF file from that: Or two, buy a copy of Pro Tools, or just download the demo, and either mix the project in that, or use it as a translator to export the OMF or AAF to the DAW of your choice. Logic Pro will reliably accept an OMF non embedded file from Pro Tools, and will sometimes accept and AAF.

It is not the end of the world if you can’t take a session export though. Your alternate option is to get the picture lock, and an export of the audio in a stereo file at the rate and bit depth you will be working, and off you go in the DAW of your choice.

Pro Tools, Logic Pro, Nuendo, are definitely good DAW’s to do post production in. I generally work in Logic Pro when I am mixing, but I have done one movie in Ableton Live. Ableton Live is powerful enough to do the work, and the tools are just fine, but Ableton does not support the OMF and AAF file format, so you will be stuck with manually importing the audio and checkerboarding it yourself. This can be 10 hours of work on a 30-40 minute film.

Stereo or 5.1 Surround?

One of the first things to establish is, what does the director or producer expect as a final output? Many low budget indie films are only looking for a stereo mix, but the mid to upper level indies that are really going for the film festivals may want a 5.1 surround mix. Make sure you ask the director and or producer up front what they are looking for and discuss the differences in budget for each. Getting set up for, or renting time in a 5.1 mix room is going to run a little more expensive, and they need to know this. If you already have a 5.1 surround sound mixing room, I would guess you probably already know most of everything I am going to cover in this article, so you can skim through and congratulate yourself on what you have learned as an audio engineer. Perhaps you might even like to share some of your experiences with us in the comments section. For the most part I will focus on what it will take for the first timers to get up to speed on a stereo audio mix for film.

Sample Rate and Bit Depth

Find out from your picture editor what sample rate and bit depth they would like the files in for your final export. Generally 48kbps sample rate with a 24 bit depth will be fine, and perhaps the highest that their system can handle. Some can handle a higher sample rate, but not many can handle 32 bit depth. Also find out if they want .aif or .wav or some other session format.

Get a Good Loudness Meter

This is more important than you think it is, unless you already know all about broadcast standards, and then it is exactly as important as you suspect. As recording and mixing engineers for albums and singles most of our dealings with mixing and “loudness” is “how loud can you make this track without clipping or squashing it too much”. Every band wants their song to be as loud or louder than everyone else’s. There is much that we could discuss about the “loudness wars” but plenty of other people have already written tons of valuable information on that already.

Broadcast Standards

In the case of mixing sound for film or television there are very specific standards that have been established, and passed into law. Cinema, and DVD can be a little more lax than television, but it has been my experience that mixing film audio to the BS 1770-3 a.k.a. A85 standards established by the CALM act works out very well. This kind of tool can guide you during mixing and help you arrive at a balanced smooth sounding mix that won’t blow up anybody’s speakers. You can always mix to the broadcast standards, and then if your client wants it louder make some easy adjustments from there.

Before we get too deep into this I want to share one little tidbit of info. In case you don’t know it yet, 1db equals 1LU or loudness unit. All the loudness meters measure in LU, so this is handy to know.

I suggest that you do a little research on loudness meters and pick the one that you think will work best with your style. Waves has one, Dolby has one, TC Electronics has one, and iZotope has the Insight Metering Suite.

I ended up choosing the Insight Metering Suite because it visually made the most sense to me, gave me easy readouts of all the information I wanted, and had a reputation of being even more accurate than the Dolby meters. I also have had excellent experience with other iZotope software, and I trust them to deliver a top of the line industry tool.

The beauty of using a loudness meter like Insight is that it has all the presets with the standards worked out for you. If you are mixing for the USA it has those, if you are mixing for the UK or Japan, it has those. If your market’s standards are not represented you can make your own preset. I’m in the USA so I chose the simple US meter preset. This gives you a max peak of -2db, a program average target of -24LU and a dynamic range target of 14LU.

There are a ton of features on this meter, but that is for another article. Basically, it shows you your targets, and gives you clear readouts of where you need to go back and refine. A good loudness meter will make your life easy and remove any worry you have of getting your program mix rejected for peaks over the broadcast standards.

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