The ever-changing standards for levels is a confusing landscape to navigate. Scott Hirsch clarifies and offers some insight for creating and maintaining broadcast vs. web vs. theatrical levels.
- [Instructor] In this movie, we'll take a look at how we can use a new breed of loudness meters, which are able to properly weight and quantify average loudness over time using a form of measurement called loudness units. We'll look at how to use these tools to mix our projects, so we can meet broadcast legal requirements, levels that are consistent with web loudness, and proper theatrical levels in the movie theater. First, let's get a couple confusing terms out of the way. Loudness units or LUs, are individual units of loudness measurement, roughly equivalent to 1 decibel.
LUFS is the new scale we measure loudness with. LUFS stand for Loudness Units relative to full scale. Sometimes you'll see LUFS, and sometimes you'll see LKFS referenced in loudness meters. LKFS are Loudness Units relative to K-weighted full scale. These differences are not super important. And the only difference between LUFS and LKFS is the scale they reference. To put it in simple terms, 1 LUFS equals 1 LKFS equals a 1 decibel change.
Now, let's talk about what loudness unit numbers you want to hit and how we can hit them to meet our specifications. The CALM Act is a legislation passed by Congress in the United States in 2010. These regulations refer to an ATSC recommended practice that specifies when mixing audio for broadcast or cable, the target loudness value should be minus 24 LKFS or the average of the piece. So, in my experience, typical specs for broadcast channels or streaming services like Netflix in the U.S., require minus 24 LKFS plus or minus two.
This means the average loudness over the whole program must hit a target value between minus 22 and minus 26 LKFS. Specs also specify a true peak value of minus two. Now this means that any instantaneous volume peaks cannot exceed minus two decibels below the absolute digital ceiling of zero. Let's see what this looks like in Pro Tools. Here I'm using one of the new loudness meters, this is a WLM Loudness Meter made by Waves.
It's one of many audio meters that are able to show you loudness in terms of loudness units and LKFS and average that over the course of your program. In this particular meter, we have a short-term window which shows you kind of what's happening instantaneously, and then a long-term window which averages over the time you play through your piece. So, let me go ahead and hit play here. This is just someone talking, and we can see where these values hit on our WLM meter, on our loudness meter.
And notice I'm referencing LKFS here. - [Recorded Audio Voice} When the vitaphone was in it's laboratory stage, a man had to beg me, farely kidnap me to get me down to hear it. We had ourselves completely sold on the theory that the picture was all in all. - [Instructor] Okay, so you saw the momentary value is going up and down but over the average we are averaging exactly minus 24 LKFS, so this is right in the perfect range for broadcast specifications. You probably also noticed that the true peak value never went above minus four in this case.
So, it remained in the specified range below minus two for our true peak value. So, this would pass a broadcast spec. But what about other forms, what about web? For the web, there really is no defined rule, it's kind of the Wild West, in terms of levels. In other words, there's no legal standards. But, I've seen average numbers be a bit louder than broadcast, anywhere from minus 16 to minus 18 LKFS. This kind of makes sense since we're compensating for people playing audio out of their phones, or computers, not loud speakers for web use.
So back in Pro Tools, if I wanted to get this up to web level, I would crank up the clip volume or the output volume, say about 60 dBs. And you'll see now where it hits here is more in the range for web levels. - [Audio Voice Recording] When the Vitaphone was in it's laboratory stage, a man had to beg me, farely kidnap me to get me down to hear it. We had ourselves.. - [Instructor] Now, you see we're hitting much higher levels more in the range of web, and I did that by increasing the volume 60 dBs in the source audio.
Now, finally, oh one more thing about web levels, so between minus 16 and minus 18, and also you want to still adhere to that true peak value. Now what about theatrical? I'm talking about movie theater levels here. This is similar to the web in that there's no real defined rule. But typically you have much more freedom in the theater for dynamic range. You can get away with being softer, and louder at times since your captive audience is in a quiet room with large full-range sound system pointed at them.
Like the web, there's no hard and fast rules, but target values tend to be lower, between minus 30 LKFS and minus 27 LKFS. Now, this brings up a good point, back in Pro Tools here, and that is that most level meters can be tuned or anchored to react only to listen to dialogue, via different weighted algorithms. In the WLM meter, the weighting is taken care of down here. And we're currently adhering to the ITU 1770, which is the ATSC recommendation we've talked about from the act passed by Congress.
This brings up another good point though, especially when we talk about theatrical levels for the movie theater. And that's that meters don't tell us everything. Even with these fancy new meters, we must still rely on our ears as mix engineers. And that's what we'll get into next week, how to calibrate your listening environment, so you can use your ears, along with your meters, to make sure your program is sounding good.