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When you are mixing audio for video you might ask yourself, how loud is too loud, how quiet is too quiet? As you are going to send your work out to the world, these are important questions to ask. By properly calibrating your loudspeakers prior to any work you do and leaving the listening volume set the whole time, you will have a baseline volume reference that relates to the outside world. This way you can use your ears to accurately determine when dialogue, effects, or music are too loud or too quiet. As a consequence your mixes will translate to the outside world and they will conform to volume level standards. The tools you will need to calibrate are as follows.
You will need an analog or digital SPL meter. You can get this at your local RadioShack. You'll also need a digital file of pink noise. This is a test tone and you can get this at a web site Blue Sky. They make professional speaker monitors and they actually offer a free bundle of test tones, which is where I got the test tone that we'll use in this lesson. So what is pink noise? Unlike white noise which is randomized noise with energy weighted equally for all frequencies, pink noise is randomized noise with energy weighted equal for all octaves.
Basically pink noise is a test tone that best approximates how we hear. Pro Tools also does have a built-in signal generator that provides pink noise. But some engineers have argued that Pro Tools tone generator isn't randomized enough for the best calibration. So instead we are using here the Blue Sky Pink Noise file which is full bandwidth at -20 decibels Full Scale. And we're using it as an audio file in our tones track. So let's talk about our loudspeakers. I want to look at a slide that shows how they should be arranged physically in your room. This is important.
First of all, you want to make sure that the speakers form an equilateral triangle between the optimum listening position, where you would be, and the speakers themselves and the angles should be 60 degrees at each corner of this triangle. You also want to make sure the tweeters of the speakers are at ear height. That's the best position for them to be vertically. If you have an external mixer or any device between your Pro Tools output and the speakers, you want to make sure that you've calibrated the output levels of Pro Tools and that device. So the way to do this is to use another test tone. This time it's just a 1 kHz sine wave also playing back at -20 decibels Full Scale.
So you have 20 decibels of headroom above this test tone and take a listen to what this sounds like. (Beep) Okay, so we're probably familiar with that kind of tone. You want to play that out of Pro Tools and you want to make sure it's coming out at -20 and you want to set that up so that if your external device, your mixer between Pro Tools and your speaker, is going to have a VU meter or an analog meter. Now remember decibel Full Scale is a digital meter at -20 and that should equal 0 VU on an analog VU meter on your external mixer.
So, you want to adjust your input trim on that mixer until -20 coming out of Pro Tools equals 0 VU, on that mixer between Pro Tools and your speakers. Then we are going to calibrate the actual level of the speaker monitors and for this we would use our pink noise. We want to position the SPL meter where your head would be in the engineer position. Then you want to set the meter to C weighting, slow response. Those are two settings that you'll see on the meter itself.
So C-weighted, slow response. You want to set your tones track to output just to one speaker. We can calibrate each speaker one at a time and then we play the test tone. (Buzzing/white noise) And as it's playing we're going to adjust the output of our speaker up or down to hit in certain SPL levels and once we get there, we're calibrated for that one speaker and we move on to the next speaker. So what are these SPL levels? Let's take a look at a chart and it shows us where we should be hitting.
For a theatrical film work, say you're mixing for a film that's going to play in a movie theater, we listen a little louder as we work in Pro Tools, and if you're working in a very large studio where you are farther away from the speakers or a dub stage for example, you are going to want to calibrate your SPL meter to 85. That's the decibel level dBSPL on the SPL meter. So you play back the pink noise and you adjust the output of the speaker until it reaches 85. Again, if you're working on a theatrical film but you're in a much smaller room, 85 is going to be a way too loud to be listening to for hours on end.
So you're going to want to actually go down to 82 dBSPL, which will give you a loud enough reference but it won't be blowing your ears off. For other type of work such as Internet, TV, broadcast, or even DVD mixing, you're going to be monitoring back at a slightly lower level. This would be 79 for a large studio or dub stage and also 79 or even 78 for a smaller room. Again, remember if you are listening back lower your mixes will tend to be a little bit hotter. It kind of works in the inverse fashion that way.
So these are again just recommended SPL levels, kind of taking a survey across a lot of professionals that I know and work with. These are typical SPL readings that people calibrate their monitors for out in the professional world. So what about audiometers? Within Pro Tools you can use a meter such as the PhaseScope here and it can be a helpful reference to ensure you're in the ballpark but it should only be used as a reference. Truth is that no meter can perfectly tell you all the info that you need all the time. As you can see here on this PhaseScope I'm referencing two things at one time, Peak metering and RMS.
These are two different styles of metering. RMS, which stands for Root Mean Square, gives you information about the average level over time and Peak gives you an instantaneous read on the loudest peaks for any given moment. In general, RMS metering can tell you more about the true loudness of your audio, so I use it to check general dialog range and when normal spoken dialog is reading somewhere in the -20 average range RMS, it's usually a good spot to start. Now I'm going to playback a piece of this sequence so we can see where it's landing on both the Peak and the RMS level.
(Background noise, car engines, crowd) You'll see the Peak meter is the green meter that's a little higher and the RMS is the blue. (Cars revving their engines) So remember that your ears are really the best reference and as long as you have calibrated your monitors like we spoke about here to output to the correct SPL level, that's really the point of calibration. You can rely on then your ears and not meters. But you can use a meter just as a general ballpark reference.
Once you have completed this kind of calibration and you work with it for a while you'll learn to better trust your ears and they will tell you where the overall levels of your mix are at. So if it sounds too loud to you it is too loud; if it sounds too quiet it is too quiet. It will take a bit of time to get acclimated, but if you work consistently in this calibration for all the projects you work on, they will give you an accurate frame of reference and it will make your mixes translate better to the outside world.
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