In a synthesizer the sound starts with the oscillator, goes through the filter and then reaches the amplifier. The amplifier is going to be changing all the time. In fact, we had many amplifying stages or gain stages throughout our mixing board and all our effects. This one is a voltage controlled amplifier. Otherwise known as a VCA. And it's designed to move all the time, and quite rapidly. And there's always a specific modulator, attached to the VCA. And this specific modulator is an envelope. We mentioned it briefly earlier. But, an envelope is basically a set path, that runs every time a key is pressed. And that path usually goes up, comes down, stays for a while and then goes away at the end of the note. Now we've used the term envelope before in the class when we were talking about a compressor, right. We had that listen side of the compressor, or the side chain, or the key side that calculated an envelope, which was kind of an average over time of the, of the amplitude of the sound going through it. If we were to refine our language a little bit, we would call the compressor's envelope an envelope follower, in that, it's calculating the average over time. But, then it controls the amplitude, and actually the volume part of that compressor is actually a VCA, a voltage-controlled amplifier. And that envelope follower, an amp was creating a signal, it was creating a voltage. That was controlling the VCA and the compressor, or the gate, or the limiter, or the expander. So we're seeing the, these ideas, synthesis kind of connects the effects and the sound creators. That's kind of a neat thing that way. So the envelope and the synthesizer, instead of following some, and calculating the sound that's in something else, it creates a path. In fact, we define a path before and ahead of time typically with four controls. ADSR, you may have seen that in a synthesizer before, read it in a, a magazine somewhere. Those 4 letters stand for attack time, decay time, sustain level, and release time. And it's important to be using that terminology as you think about ADSR. Because it can be a little difficult. We have another one of these examples where words mean different things in different contexts. And when talking about synthesis, attack is something very different then when we, what we usually have. Like when I'm talking about a drum, if I would say it's more attack, I'd say it was sharper right? It was louder at the beginning. But, if I, on a synthesizer, if I increase the attack time, it actually dulls the beginning of this note. So, we want to be very careful with our terminology and know what's going on with that envelope. So again, it's attack time and that what's going to happen is every time you hit a key, the envelope is going to run from zero up to a full value in the time of the attack time. So it'd be at it might be 5 milliseconds, maybe 10 milliseconds, maybe half a second. But the more you increase that attack time, the slower it's going to ramp up. The next thing I'd like to jump to is the S part of it, which is the Sustain Level. Now all the other knobs are time in this envelope. But the sustain is a level. So, another reason to remember attack time, decay time, sustain level, release time. And the sustain level represents kind of a steady state, that the note stays at while it's being held. Now this is useful when trying to repricate say, a violin sound. The note starts with a, a nice aggressive bow and then it kind of rests at a steady sustaining state, and we set that kind of level with a sustained level knob. Now there can be some time to get from that full value down to the sustained level. That's our decay time. And then when we release a key the note, the sound has to release down to zero and that is our release time. So again there is always an envelope attached to the main amplifier. And that envelope controls how the volume of the amplifier changes over time. It's controlled by 4 paramaters: Attack Time, Decay Time, Sustain Level and Release Time. Attack time is the time it takes to get from zero to full value when you press a key. Decay time is the time it takes to get from full value down to the sta- -- sustained level. When you release the key, you enter the release phase, and the release time is the amount of time it takes to get from the sustain level down to zero. Let's look how this functions in our basic synthesizer. Again, we're going to move into a synthesizer and I'd like you to locate the main amp envelope on your synthesizer. Now, envelopes are general purpose modulators. Meaning you can have many envelopes, and they can be controlling many different things within your synthesizer. Very often the last envelope in your synth will be your main amplitude envelope. Now the synthesizer we have in front of us has a very nice display, for how the envelope is functioning. On many synthesizers you have to know what the envelope shape is, just by seeing four knobs or faders labeled a, d, s, and r. So while some synths give you a nice visual of the amplifier envelope, many just give you those 4 faders and require you to know it. So let's see how ADSR works. On this patch, I have a saw tooth wave form that is being heavily filtered, and let's hear it. [SOUND] I'd like to point out something about this display. The yellow bar at the top is showing you my note on and note off, so when I play a mini note on, you'll see that yellow bar start and when I release a note, you'll see the yellow bar stop. Right now, I have configured what I would consider an organ envelope. It functions like a switch and it's just like an organ, like a Hammond organ does, you press the key, the note starts, you release the key the note stops as fast as possible. And we configure that, by putting our attack time at zero, our decay time really doesn't matter, but we'll set it low, sustain level all the way up, and release time, very low. Now as we do this, we might run into an issue, let's hear. [SOUND]. You may find, on some synthesizers, that you get a slight click when you have attack and release set that fast. So, you may find that just a little bit of attack time and a little bit of release time, will help remove the click at the beginning and ending of notes sss. The next thing we might want to do with this patch is make it swell in. Now, this is kind of an unusual type of envelope. There's not many natural sounds that do this, but this emulates reverse sounds quite well. If you take a cymbal sound and reverse it, you get a swelling in kind of character. And again, we can emulate that by increasing attack time. Let's increase attack time way up here and see what happens. [SOUND] So we see Node On, started here, the sound swelled in slowly and when I release the key, it stops immediately because the release phase happened. Now I'd like to point out something right now. You'll notice, when I play an attack [SOUND], the sound went up in a straight line. That's because this is a very simple synthesizer. But you find that those kind of details vary from synth developer to synth developer. You might find some synths where that's more of an exponential increase, some that's more of a logarithmic increase, but those little details of how the envelope actually functions really can make a big difference in the sound and does vary from developer to developer. So we said that increasing attack time is, kind of, unusual. Very often that's set quite quickly. The next thing we might want to do, is make the sound last when we release the key. And that's going to be by adjusting the release time, so if you open up a patch and it just stops way too quickly. Maybe you have to increase release time. Or if you have a patch that tends to hang on after every note, reducing release time is often the best choice. Let's try it here. I'll increase release time. And again, remember the yellow bar at the top is the note on and note off. I'll play a key. [SOUND] The note starts. I'll release the key. And this sound gradually goes down to nothing. If I to, put a very high release time, [NOISE] release the note, and it decays away slowly. Again, the shape of that release can vary from developer to developer. So, let's set another, let's set up another patch, and the next kind of patch I like to look at, is what I would call a percussive sound. So the sounds we've been developing now hold on while you're holding the note. We call those sustaining notes. So a sustaining synthesizer patch would be good at emulating things like strings or brass. Things that can hold a note, or add energy to their system as the note holds on. Real instruments that are blown or bode will have a sustaining envelope. Because they're adding energy to that note as the note continues on. If I have a sound that's, that's plucked or hit, then there's no energy being added over the course of the note and we bring Sustain Level all the way to zero. Now when sustain level is at zero, we're going to use Decay Time to control the length of the note. Let's try it out now. I'll hold the long note on my keyboard. [SOUND] And it just decays away. You can see from the yellow bar that I'm still holding onto the note, and I can release it. Nothing really changes. That's because the decay time controls the length of the note now, because sustain is at zero. So again, this kind of envelope is good for creating, kind of, plucky, or hit sounds. Because energy's added to that system once, and is let to naturally decay. If I want to create kind of a sound that's a long, has a longer decay, I increase decay time. [SOUND] Now, what happens if I release the key during the decay phase? Let's see what happens. [SOUND] If I release the key in the middle of the decay phase, the release phase starts from that point. Let's try a little bit longer of a release time. [SOUND] We see we have the end of the note, and then the release time starts. So the release phase will start, at the level, that you release the key, no matter where that is. What we've actually created now is a damped percussive sound. Kind of like, a piano. On a piano when you play a key. The key starts and it decays away naturally, right? You're not adding energy to the system that wouldn't be a sustain level to it because energy is decaying away. But when you release the key, the dampers on the keyboard come up and stop the note. So we've created a damped percussive sound. If we would like this to be a truly kind of percussive sound, where the length of the note you're pressing doesn't really matter, usually you would set release time close to decay time. They're set about the same. And this way [NOISE] when you release the key, it changes a little bit but it's pretty much the same. On some envelopes you'll have a one shot option which makes it so it doesn't matter at all how long you hold the key, it's going to play that envelope straight through no matter what. That's a great feature if your synthesizer envelope has it. The other kind of envelope we're going to be setting up very often is a sustaining envelope with a strong attack. And this happens on most sustaining instruments. If I'm blowing into a trumpet there's a loud initial burst of air, and then it settles down into a sustaining state. Same thing if you're playing a bowed instrument. You're bowing a violin. There's a strong attack, and then it settles down into a sustaining state. If we want to create that sort of sound, for bowing or blowing, we're going to be using all the phases of the envelope. And I'll set sustain level somewhere in the middle. In this case, we'll see the kind of standard diagram of an ADSR envelope. And we'll see that we have attack time is very low. And then it'll immediately decay down to the sustained level, stay there, until I release my key, and then the release phase starts. Lets see. [NOISE] Stays there, I release the key. [NOISE] It decays away. If I want that to be kind of a punchier sound, I can reduce the decay time, [NOISE] and I get a strong burst at the front, and then I release the key I get release time. If I want it to go away quicker, I reduce release time. [NOISE] Now there's one more envelope I'd like to show you. And this is a kind of fun one. It's unusual. It's really, I've never used it in a real context. It's only happened to me by accident, but it points out a really interesting quirk of the amp envelope. In fact I call it, the Quirk Envelope. And we get this, by setting Sustain Level all the way down, but Release Level very high. And decay level very short also. So we have no attack time. A short decay, but a long release. Now, the strange thing about this, is, if I play a long note, [SOUND], we just get a short blip. But if I play very quickly on my keyboard, [MUSIC], we get a long decay. Again, a long note. [SOUND] And we get a short blip, or if I play really quickly, [SOUND] we get a long decay, and that's happening because remember, the release phase starts right when you release the key, no matter where the envelope is. So in this instance, if I play a short note, I get a long result, and if I play a long note, I get a short result. Kind of a strange kind of envelope, and I, I learned it because it happened to me by accident. I'd like you to go to your DAW and try to work with the amp envelope. This is one of those really important features you're going to have to know because it's one of the best ways to take a patch that's almost perfect, and make it perfect.
