Exploring filters - Logic Pro Tutorial

- [Instructor] In synthesis, sometimes taking information away is just as good as adding. In this movie, we'll explore how we can use filters to carve away the rich harmonics we use additive synthesis to build. As you'll see, the results of using filters are pretty cool-sounding. And they're crucial to all the synth sounds you know and love. If you're familiar with the concept of equalizers, or even just the treble and bass knobs on your car or home stereo, you already understand the basics of filters. Filters are actually equalizers that work to manipulate the range of frequencies in an audio signal. Filters on synths are often pushed to the extremes to make the effect way more obvious than the subtle equalizers you might be familiar with. There are four main types of filters we'll typically encounter on synths. Make sure you pay attention to their names or initials, and also the shapes of the graphs here, because one or both will be used as a parameter on the filter section of our synths. We'll start with the low pass filters, also known as LP or LPF. Let's look at it on a graph. On this graph, we have the frequency across the X axis from low, or low-pitched or bassy on the left to high pitched or trebly sounds on the right. The cutoff point is where the filter starts to cut away the high frequencies and allows the low frequencies to pass. Hence the name, low pass filter. Notice the shape of the filter on this graph. Now let's look at an example in Logic's Retro. Here in the filter section, we have the shape of our filter, and surprise, it looks quite similar. Here's where we can choose the filter types. Let's choose a low pass, LP 24 dB. The 24 stands for the slope order. 24 is a pretty steep and dramatic slope for maximum effect. Numbers less than 24 indicate a gentler slope. Now notice the shape resembles the graph we just saw. Again, we're going to allow low frequencies on the left-hand side to pass through while we carve away high frequencies on the right. The crucial parameter for this, and almost all the filters we'll see, is the cutoff frequency and where that occurs. And we can change that by just clicking and dragging on the cutoff parameter. And as I do that you can see the little dot moves left to right. You can also grab hold of the little dot and just move it around with your mouse. Let's play back this sequence I have here and hear what it sounds like as I move the cutoff filter. I'm just going to turn down the volume a little bit. And here we go. (electronic synth music) Now as I move to the left, we're removing high frequencies, letting just the low ones pass and the sound gets kind of darker. As I move to the right, we're allowing more high frequencies in, and the sound gets brighter. (filtered synth music) One other crucial parameter to this type of filter is called resonance. Basically, as you increase resonance, you're adding volume to the frequencies directly on or near the cutoff point. You can see this visually as I increase the resonance parameter here. If I click up here and drag upwards, you can see that it's increasing the volume of the frequencies right at the cutoff point. Now let's listen to what this sounds like as I move the cut-off point around. (electronic synth music) This effect, which you've probably, pick up. Now, this effect, which you probably recognize, sweeping a low pass filter with a high resonance, is widely used in all forms of electronic music. Let's move on to another filter type. The high pass filter, or HPF. The cool thing here is we already know everything about how this filter works. It's exactly the low pass filter in reverse. Instead of allowing low frequencies to pass, we allow high frequencies to pass while we cut away the low ones. And just for the sake of showing you how these filter types exist on different synths, let's look at the high pass filter in Ableton's Analog synth. So here we have our filter section and notice I have it set to HP 24. If I open this up, you can see all the different filter types. We have our good old low pass friends that we just learned about, and we have high pass. Let's start with the high pass to demonstrate that. I've got this same sequence loaded up. And as I move the frequency point, we'll hear a similar thing. It's going to be allowing high frequencies to pass while we cut away low frequencies. (electronic synth music) So right now we're hearing mostly high frequencies. And as I move this parameter lower, we're letting more and more low frequencies in, until we have all of them. Notice I have a bit of resonance here. And I'll move this up and sweep it. (filtered synth music) So it's a similar effect, but just moving in the opposite direction. Another important filter we should learn deals with the stuff in the middle. These are called band pass filters, usually referred to as BP. And really, band passes are nothing more than a high and low pass working together, allowing a band of frequencies to pass through the middle. Let's see how a band pass looks in Retro. So I'm going to switch over. Instead of low pass, I'm going to go down to the band pass filter. And I'll choose the, how about the band pass 12 dB edgy? And there you can see, it's just cutting away lows and highs and I can move the cutoff point to somewhere around the middle. Let's take a listen to what this sounds like. (filtered synth music) So we're doing a low pass and a high pass effectively with this band pass filter. One other important filter is called a band reject or a notch filter, it's sometimes called. And in this one, if I go to the BR, band reject filter, you can see how this works. It's actually cutting away just a certain band of frequencies in the middle, rejecting those bands. And that sounds like this. (filtered synth music) So it's a little bit more subtle, but effective as well. Now one last filter I want to show you is called a peak filter, which adds a spike of a specific frequency in the middle of the range. Here, we can see this peak creamy filter does exactly that, just adds this spike and then get a similar type of effect. (filtered synth music) So now that we understand how the most common synth filters work, having control and carving out the frequencies of the sounds your oscillators emit is a large part of synthesis. And as we've seen, moving or automating the cutoff and resonance parameters in real time is an awesome sounding effect. And we'll explore that concept in the movies to come.