[SOUND]. Wow, what's this? It's a drum machine. So what, what, how does a drum machine work? Well, let's figure it out. So, a drum machine has a pattern, pattern which specifies what rhythm it's going to play. And the way that you, you, you input that pattern is using these colored buttons at the bottom, okay, so this is, this is a tra2a, it's the classic drum machine. And you can see, you've got 16 buttons on the bottom there. So if you, if you press a button, and a light comes on, and that means that on that beat you're going to trigger a sound. And then, a clock will step it through the beats, and if it sees that the button is on, it will play a sound. So, what we're going to try and do is emulate that kind of behavior. What we call step sequencing inside processing. So, we're going to have to figure out how we're going to represent that sequence int he memory, we're going to have to figure out how to do the clock and various other things. but it's really nice because if you do it at this low level you have complete control over how the sequencer works. And that means you have a much wider range of possibilities to get creative. So, let's get into some code. So, I've got a basic starter code here. And you can see I've got the usual maxim object. And I've got an audio player, which I'm calling snare. Which will be obvious why shortly. And then, so I create my maxim. And I create my snare. So, I'm loading in wav files. So, this is I believe it's a sample from the Roland TR-909 drum machine. but you can obviously use any samples you'd like. But certainly for a drum machine you probably want to be using short samples. So, that's my snare sample. And then, my frame rate, I'm setting to 30. that could be, that could be set to anything. But I'm just setting it to 30, so it's really explicit how the timing is working. Okay. Then, I've got this variable called playHead, which I'm setting to 0. And playHead is, is how I'm going to figure out when, when to trigger events. Okay? So, when draw gets called, which happens repeatedly. Remember, draw is just being called all the time. The playHead is going to go up by one. And then, I'm going to check if the playHead, how far the playhead has gone, and if it's gone up to 30, in other words if I, if I take the remainder of the playHead in 30 then, and it's 0, that means that it must have got through three calls to draw, sorry, 30 calls to draw. So, that means because it's 30 frames a second that means one second has passed. So, this little if statement here, checks if a second has passed, okay. And so, when one second passes, I queue up the snare drum sound and I play it. So, the, the sound we expect to hear from this is a snare drum being triggered once a second. [SOUND]. Okay, there you have it. Now, that's not really the best rhythm I've ever heard. so, I think quite a few songs aren't that far from that rhythmically, but we can, we can do better. So, what we need to do now is, is address that problem I mentioned earlier which is how to represent a sequence in the memory. So, the way I'm going to do it is I'm going to take a Boolean array and call it snare, snSeq, like that, so I'm giving it a kind of short variable name so I don't have to keep typing it in, okay. So, snare sequence. Now yes just to reiterate it's a Boolean, so that's going to contain trues and false values. Because the idea is that it, remember with the buttons on that drum machine we saw at the beginning they're either on or off. So, Boolean is fine. And it's an array so that means you can install several Booleans in one place, which makes it more convenient. So, let's initialize it. snare sequence equals new boolean. And I'm going to put four slots in it, and then I'm going to put a rhythm in. Equals true. So, it's going to play a snare on the first beat, let's put four beats in, one, two, three, and this, they're going to miss it on the second beat and it's going to trigger it on the and then two, it's going to do two. So, the idea with this rhythm, it's true false true true. So, it's going to be like this. [SOUND]. Okay? So, we get three in a row, and then a, and then a gap. Right, so let's, so the problem is I now, I now need to look into that array as my, as my, my ticking clock, you know, my playHead. Every time playHead gets to zero, I need to figure out where I am in the array. So, I'm going to need another variable which is it's going to be called snSeqPos, okay? So, snSeqPos is going to start off at 0, okay? Now I'm going to, want to do is every time the the playHead tells me it's time to, to, to play a sound, I'm going to increase my, my sequence of position by one. Right, and then, I'm going to check if its gone too fast, snSeqPos. So, I'll do a check. If, snSeqPos is equivalent to snSeq.length, so in other words, if I've got up to four which is a remember from Marco's lectures about arrays that arrays are zero index. So, we don't want our index to go up over four and this is our index. so, so we check if it's gone that far. If it's gone that far then we reset it. Okay, so that, that code there is, if you like, a simple thing which steps through from zero to three then goes back to zero again. So, we can just check that code by, by testing, so let's print line position. And let's print it out, snSeqPos. Okay, so we should see it going zero, one, two, three, zero, one, two, three. So, let's run that. Save and run. [SOUND]. Okay, so you can see that's going, that's counting zero, one, two, three, and back to zero again. Okay. So, we've got our in, so we can now use that to index into the array. So, we go snSeq. And so, what we're going to do is basically if there's a true value in the in out sequence there, then we trigger the sound. So, snare sequence, seq snSeqPos. this is equivalent to true, but we can actually, we don't need the equivalent true because we can just put it directly. because remember in an if statement you can put a Boolean directly in there. But let's make it really explicit. And there's different styles of coding, some more explicit than others, so let's be really explicit. and just check if it's true, then we're going to play the snare. So, remember that beat I mentioned earlier? So, it was one, two, three, gap, one, two, three, gap. Okay. So let's see if we can get that -- that going now. So, I'm going to run it. [SOUND]. So, you can hear it's got that gap, but it's too slow so I'm going to speed it right up. So, I'm actually going to just double my frame rate and that should speed it up. Okay, let's save. [SOUND]. Okay, so the, the rhythm's a little bit irregular. That's because I'm doing a screen capture at the same time. So, if you're just running this in a normal browser it should be fine. And okay, so, so we defined a basic sequencer which we can we can use to trigger different sounds. So sounds at different times. Now so the programmer can edit the sequence and make it longer and so on and you can make a really elaborate rhythm sequence. And it's obvious that you can also add another Boolean array. And then you need another another position counter, and then you an add more and more tracks. So, that will allow you to build a full multitrack drum machine. And I'll leave you to go and have a go at doing that, and, and we'll show you a kind of fully worked example later. [MUSIC].
