Though we can trace filters back to delay, they really form a category of themselves in any kind of practical sense, and we find that manipulating the temper or the spectrum of our sounds becomes one of our really important mixing tools. And a contemporary EQ plugin that we'd find in a DAW is really a collection of filters, all designed to work together so that we can really finely craft the spectrum of any one of our tracks. Before we get into the musical uses of the EQ, I'd like to just, figure out what those individual filters are that make up one of these complex EQ devices. We find that a contemporary EQ is designed with a series of bands. And each one of those bands is a, an individual filter. And most times the bands themselves can be changed through a variety of these filter types. The first set of filters that we have are our pass filters. And they're designated with terms like low pass, high pass, and band pass. And what that term really means is, what is the filter letting through? You can think of it kind of like a doorway. What does it let to pass through, and what does it stop? So if I think of a low pass filter, it's going to allow the lows to travel through, the low frequencies to travel through, but it will attenuate, or lower, the high frequencies. High pass filters allow the high frequencies to pass through, but attenuate the low frequencies. And a ban pass filter allows a range of frequencies to pass through and attenuates the low end and the high end. These terms often give people trouble, 'cuz it seems a little bit counter intuitive to talk about what the filter's letting through. Usually we'd talk about what the filter is actually reducing, but with a pass filter you're saying it's letting these frequencies through. The highs are passed through. The lows are passed through. A band of frequencies is allowed to pass through. So practice it yourself a little bit. I sometimes get tripped up on the words. It's alright if you do, but try to get into the habit of using the terms because it's better than saying a low cut filter. You want to say high pass. That's the proper terminology. Now, these function as kind of removal filters, they're very drastic and they function like this. We establish a cut off frequency, which is the frequency at which the filter will start functioning. So, let's see I am working on a low pass filter. I establish a cut off frequency, let's say, 100 Hertz. And then I'll give a categorization of that filter. We'll say it's a 12 decibel per octave low pass filter. That means for every octave I go above the cut off frequency the amplitude will be attenuated by 12 decibels. So if I'm at 100 hertz, if I go up to 200 hertz, which is an octave above 100 hertz. The amplitude will then be attenuated by 12 decibels. If I go up another octave to 400 hertz, we're now going to be down to negative 24 decibels. If I go up another octave, it's another 12 decibels down. So you see the further you get away from the cut-off frequency the more it cuts. It's very drastic and by the time you get a couple of octaves away, the sound is basically gone with those. So they're very drastic. They're used a lot in synthesizers. But we, they, they have limited usage in a mixing context. Because they're so drastic. The next kind of filters we use very commonly in a mixing context are shelving filters. And a shelving filter, while a pass filter might be a, a removal filter, a shelving filter is like a reduction filter in that it'll reduce the frequencies above the cutoff frequency for a high shelving filter and will keep it at a set point. So I can say my cutoff frequency is 100 Hertz, and I can say I want to go down by six decibels. And then from that point on all the way up the spectrum it'll be down by that amount. So it's just reducing the high end, not removing it entirely. So shelving filters are reduction or boost. but consistent across the frequency range. And past filters are very drastic. They're really going to remove certain frequencies. And shelving filters are used all the time in a mixed context. They're really important for us. The final kind of EQ, or filter, that I'm really interested in this lesson, is going to be a parametric EQ. And these are what you're going to find in the mid range. We tend to use shelving filters for the high and low end. We tend to use the high pass filter on the bottom end, but all that really important musical mid range, that's where the parametric EQ really comes in handy. It creates kind of a bell shape bump or notch in the frequency response in the frequency range. And we could adjust the width of that notch and the height of it and the, the depth of it. So, all these things work in conjunction to create a modern parametric EQ plugin, and we're going to explore one now in a little more detail on the screen movie. The first thing you can do in most EQ plugins is enable or disable a specific filter. This is important because by disabling unused filters you're saving quite a bit of CPU resources. The first important type of filtering we're going to have in a mixing context is going to be a high pass filter. A high pass filter drastically reduces the energy beneath the cut-off frequency, and is great for removing rumble and excess noise in a recording. We're going to find that not matter what filter you're using, you're always going to be having a cut-off frequency. This is the center location of a bell curve, or it's in the pass filter, it's the point at which it's already cutting three decibels. So you'll see, if I set my cutoff frequency at 200 hertz, the signal is already reduced by three decibels at that point. The other parameter we have on a pass filter is how steep the slope of the curve is. And this is measured in decibels per octave. Right now I have a 12 decibel per octave slope, which means if I go one octave below this 200 hertz. Point, which is the cut-off frequency, it will have already cut 12 decibels. And we see that we are reducing by 12 decibels at this point. If I was to increase this to a 24 decibel per octave filter, if by going down to that 100 point, 100 hertz point, we will see that the sound is already cut by 24 decibels at that point. Let's hear the impact this has on some white noise. I'll start this low, and I'll slowly increase it. [SOUND] [NOISE] As we increase the high pass filter. [SOUND] As we increase the high pass filter the bottom end is reduced progressively. The next type of filter I'd like to look at at is a shelving filter. While we do have a low pass filter in most EQ plugins, they're not used as much in a mixing context. Instead, we tend to use [UNKNOWN] filters on the low and high end. So, we'll move next to the low [UNKNOWN] filter. A shelving filter if we boost, or cut, will not aggressive reduce the further you get away from the cutoff frequency. Instead it will reduce to a point and then stay that level, continuing on creating a sort of shelf in the frequency spectrum. This is very useful for reducing or boosting the bottom or high end. And we find ourselves using low shelving filters and high shelving filters very often in a mixing content. Because we can boost or cut at that cut off frequency. We've added, another parameter which is going to be the amount that we're boosting, or cutting. In general you'll find that cutting is more useful than boosting and that you can do more drastic with your cuts. And if you're boosting you want to be more gentle, otherwise the plug-in is going to sound very obvious. Some shelving filters like this one give you the ability to change the slope of the shelving filter. On some filters that's fixed, others you do have that ability, and it is quite nice to control the kind of slope of that transition into or out of the filter. So, a low shelving filter becomes one of our really important bottom end controls. The next filter we can look at is our high shelving filter, and that functions very much like the low shelving filter, but as you can see it controls the high end. And we can boost or cut the high end, and again you have control over the pass band, how wide, how long it takes to transition to that new cut. Let's hear how the high shelving filter functions on some noise. I'll put my cut off frequency at 2000 hz. Zero db of gain. And let's hear some noise. [NOISE] And I'll increase the gain of the high shelving filter. [MUSIC] So we brought up the highs. And this is the kind of high that you'd find in a treble control on most consumer radios. A treble ad bass control, that's related to your high shelving or low shelve filters. Again if you are boosting, I would suggest boosting a maximum of six decimals, and if you are cutting maybe you can cut up to around twelve decimals. But again use your ear and be careful. The final type of EQ I'd like to look at in this segment is going to be the bell-shape, or parametric, EQ. This is going to be the most complicated EQ, and it's also going to be the one that we really have to use carefully in the middle range, which are those really important musical frequencies. This filter will have the same type of controls that we have in the shelving filters in that we have a cutoff frequency. We have a gain where we can boost or cut. And our final control is our Q or bandwidth control. And that allow, that allows us to control the width of the cut or boost. Now, I would suggest using a Bell filter to really examine and explore the frequency range. It's good to start getting your ears comfortable and connected to the actual numbers that you're seeing in your EQ, and this is one good way [SOUND] to do it. Create for yourself a fairly narrow [SOUND] Fairly high boost. Play white noise, and sweep [NOISE] The frequency range, and watch very carefully the numbers, as you're listening to the noise. [NOISE] [SOUND] For a mix engineer it's very important to start correlating the sound of specific frequencies with the numbers. And the only way to do so is going to be experimenting in that sort of way, really trying to make a connection between the number of hertz and the audible result. Now in a mixing context, you would never really use 15 decibels of gain in a bell shape like I have here. But its a great way to start training your ears. And then try it the other way, try to hear what a reduction at specific frequencies sounds like. This one, you might want to use a little wider queue for because it is quite difficult. But eventually, you'll find its quite useful. [SOUND] To me that moving notch filter like that, that's another thing we can call that is a notch filter. A very deep narrow reduction. It sounds a lot like that phaser example that we tried earlier. So those are the types of filters that you can, that you'll find in a standard EQ plugin. Hopefully starting to make sense how they function. Next we'll look at how we might use them in a mixing context.
