Lately I’ve been reading a lot about curves. No, not those. I’m talking about the Smiley Curve and the Equal Loudness Curve, which is also known as the Fletcher-Munson curve. Simply put, the Fletcher-Munson curve illustrates the relationship between sound levels and frequencies, and how we perceive loudness.

If I played you a 1 Khz sinewave at a certain level, and a 200 Hz sinewave after that, I’d have to adjust the level of the 200 Hz sinewave for you to perceive it as being equally loud to the 1 Khz sinewave. To plot this out in a graph, we’d have to repeat this process with more frequencies. Since loudness perception is personal, we’d have to do the experiment with more people. I’ll leave the science for now, I’ll post links to some articles at the end of this post, so you can get as scientific as you want.

How does the Loudness Curve sound?

Look in your presets in Channel EQ. Under EQ Tools, there is a preset called ‘Loudness EQ’. It looks like this:

The low end gets boosted, the mids are cut, and the highs are boosted. It reminds me of the loudness button my stereo had back in the day.
Consider this a very rough representation of the Fletcher-Munson curve. To play around with this curve a little, let’s seize the moment and learn how to assign multiple control parameters to just two knobs or faders, so we’ll get to control a loudness curve with just two controllers. The Caps Lock keyboard simply won’t do here (although it could), so I’m going to assume you have a keyboard or USB controller nearby. What more fun could we have?

One Knob, Multiple Parameters

Put a Channel EQ on Output 1-2, and load the ‘Loudness EQ’ preset.

Hit ⌘+L to open Easy View. Let’s assign everything in one go. Click the parameter first, then move your controller knob or fader. Start with the Low Shelf gain, then do the peak 2 gain, and finally the High Shelf gain. If you’re unsure about which is which, you can always switch ‘View’ to ‘controls’ in the Channel EQ plugin. Use one knob or fader only. When you’re done, disable ‘Learn’. We’ll want the mids to go down instead of up, and for this we need Expert View. It’s probably active after you disabled the ‘Learn’ button, if not, hit ⌘
+K. Select the controller assignment for the Peak 2 Gain parameter. Enter a value of -1.00 in the Multiply field. Move the knob to test if it works. Peak 2 Gain should now be moving in the opposite direction. Good!

Finetuning Controllers: Multiply

Let’s see if we can get some control over the frequencies by assigning the frequency parameters to a second button or fader. Repeat the process I described in the previous paragraph, this time for each frequency parameter: Lowshelf Frequency, Peak 2 Frequency, and High Shelf Frequency. Disable ‘Learn’ and see what happens when you move the knob. You’ll notice immediately that each frequency’s range is too large. Again we’ll edit the ‘Multiply’ field. I used 0.30 for the Low Shelf, 0.69 for Peak 2 and 0.89 for the High Shelf. Move the knob to see how it works out.

Finetuning Controllers: Min/Max

There’s more finetuning ahead! Let’s limit the value range of the knob for each frequency parameter. Your knob or fader sends out values from 0 to 127. This range can be edited by adjusting the Min/Max value. When the Min/Max value is adjusted to say 60/99, everything outside of that range will be ignored. For the Low Shelf, Peak 2 and High Shelf frequencies respectively, my values are 0-64, 64-100 and 80-127. These are all guides. Check the behaviour of your knobs, play around with different values a little to get a feel for it.

Remember we put the Channel EQ on Output 1-2? The consequence of this is that every time you put a Channel EQ on an output channel strip, the knobs or faders you just set up will control a loudness curve on that EQ. This is probably not what you want, so we need to look into organizing our controller assignments with Zones and Modes. This can get confusing at times, I’ll keep it simple.

Zones and Modes

In Expert View, create a Zone. I called it ‘My Zone’. In that Zone, create two modes. I called them ‘Loudness Mode’ and ‘Empty Mode’. The assignments we created are in ‘No Zone’, which means that they are always active. Select ‘No Zone’, then select all the assignments, and copy and paste them into ‘My Zone’ >’Loudness Mode’. So now we have two modes, one with our assignments, and one without any assignments which enables us to bring everything back to the state before we started playing around. Next, we need a controller to switch between these modes. We need this to be always active, so we’ll put this into ‘My Zone’>’No Mode’. Hit ⌘+L, press a controller button (if you don’t have any use a MIDI key or the Caps Lock keyboard), then set ‘Class’ to ‘Mode Change’, and set ‘Mode’ (under ‘Multiply’) to ‘Rotate’. Disable ‘Learn’.

Do I need to save?

Nope. Every time you quit Logic Pro, controller assignments are saved in a ~/Library/Preferences/com.apple.logic.pro.cs file. Once your custom assignment setup gets larger and larger, I do recommend making backups of that file, because it’s fairly easy to accidentally delete assignments, and there’s no Undo.

Have fun.