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Propellerhead Reason Subtractor Synth - Using Envelopes (Part 1)
Written by Matt Piper - © 2007, Cengage Learning. Reprinted with Permission.
This article is an excerpt from the following book: Using Reason's Virtual Instruments: Skill Pack.

When discussing sound and sound synthesis, the word envelope is used to describe the shape of a sound over time. The Subtractor has three envelopes to play with: the Amp Envelope, the Filter Envelope, and the Modulation Envelope. You may be wondering what I mean by an envelope describing the shape of a sound over time. Imagine striking a large bell with a hammer. Think of the sound of this event happening in real time. At the beginning of the event is the initial strike. In envelope-speak, this is referred to as the attack. After the attack, the sound begins to fade out, or decay. This vocabulary, as you will read below, has been expanded to incorporate more detailed concepts, but you are probably starting to get a feel for where this is headed.

When we want to affect the volume (or amplitude) structure of the sound event over time, we will adjust the Amp Envelope. You may have been thinking in terms of volume or presence of sound as you considered the bell example. When we want to affect the tonal or frequency characteristics of a sound over time, we will be adjusting the Filter Envelope. And, of course, if we want to affect the manner in which modulation is applied to the signal over time, we will use the Modulation Envelope.

ADSR: Four Letters You Cannot Live Without
ADSR—these four letters stand for Attack, Decay, Sustain, and Release. Please say the words to yourself a few times if this concept is new to you. From here on out, you will see these four parameters again and again throughout Reason, and also on just about any analog or emulated analog synthesizer you ever use in the future. With these four parameters, you will sculpt quite a bit of your sound. If you take away nothing else from this book, I hope at least that this section will be clear in your mind for eternity. If you tell someone that you read this book, and that person asks you to show him how ADSR works in Reason, and you are unable to do so, then we will have both brought shame upon me, my ancestors, and all my future generations. No pressure, but with that in mind, please read on.

Amp Envelope
Perhaps the most familiar area in which to play with ADSR is the Amp Envelope (see Figure 1.13). An amplifier, in audio synthesis, makes a signal louder by increasing the amplitude of the signal. If you are looking at a sine wave on an oscilloscope, the amplitude will be the distance between the highest point and lowest point of one cycle of the sine wave. A shorter distance means a quieter signal, while a greater distance (a "taller") sine wave will result in a louder signal.

While the Subtractor's Level control affects the overall volume (or amplification) of your sound, the Amp Envelope controls the shape of how that amplification is applied over time. Will the sound start sharply when you strike a key, or will it fade in slowly? Will it end abruptly when you let go of the key, or fade out slowly? Is a short sound produced, like a drum hit, or is a long, sustained tone produced, like holding down a key on an organ?

Here is how ADSR relates to the Amp Envelope. You can refer to this when considering other ADSR envelopes as well:
* Attack — The amount of time it takes for the amplitude of a sound to climb from zero to its peak level.
* Decay — The amount of time it takes for the amplitude of a sound to fall from its peak level to the level determined by the Sustain parameter, assuming you keep holding down the key(s).
* Sustain — At the end of a note's decay, the Sustain value determines the level at which the amplitude rests as long as the note is being held.
* Release — The amount of time it takes for the level of a sound to drop to zero from whatever level it was when you let go of a note.

The following exercise should make this all quite clear.
1. Start with an empty rack. Create an instance of the reMix mixer by choosing Mixer 14:2 from the Create menu, and then create an instance of Subtractor. In the Subtractor's Patch Browser window, it should say Init Patch.
2. Turn the Freq (frequency) slider on Filter i all the way up. In doing this, you are actually deactivating Filter Why? Because the Filter Type control on Filter r is set for LP 12, which you know stands for 12-decibel Low Pass. It allows low frequencies to pass unaffected, while filtering out high frequencies (any frequencies above the frequency chosen with the Freq slider). So when you turn the Freq slider all the way up, there are no frequencies above that to be filtered. It's wide open.
3. Change the waveform on Oscillator i to a Square wave. This should be slightly less grating than the Sawtooth waveform. It's also fun if you know how to play any classic video game music, such as the Mario Brothers music.

Now that we can hear our naked square wave without any bells and whistles to confuse the issue, we are ready to explore ADSR in the Amp Envelope:
1. By default, the Attack setting on the Amp Envelope is all the way down at 1 (fastest/shortest attack possible). So when you hit a key, you hear sound instantaneously. Please move the Attack slider up to a value of about 69 (a little over halfway). Depress a key on your MIDI keyboard, and you will now hear that the note fades in slowly. Feel free to experiment with different values to get a feel for this.
2. Turn the Attack back down to zero, and also turn Sustain and Release down to zero.
3. Set the Decay to a value of about 5o. Not such a long note anymore! If you turn it down even lower (to any value between zero and 20), the note will be so short as to sound like a percussion instrument. I have mine set at 20 right now, and am amusing myself by playing "Popcorn," the whimsical, pioneering electronic dance mega-hit by Gershon Kingsley. This song was originally played on a Moog synthesizer, by the way. (Google this stuff if you don't know about it!)
4. With your Attack still at zero, and your Decay set at 20, turn up your Sustain level to 5o. Hold down a key. You will hear the sharp attack and the quick decay, but the decay will no longer fall down all the way to silence. It stops and holds at an intermediate level. Now turn up your Sustain all the way. When you hold down a key, the sound stays at its maximum level until you let go. Theoretically, the Decay setting would still allow the level to fall to the value designated by the Sustain slider, but since the Sustain value is set at maximum, there is no place to fall!
5. With Attack still at zero, Decay at 20, and Sustain at maximum, move the Release slider (which should still be at zero right now) up to a value of 6o. Now strike a key and let go. Notice how the note continues to fade out after you release it.
6. Move the Release slider up to maximum. Now hit a note or a chord, and hear it sustain forever (almost)! Before this drives you crazy, turn the Release slider back down. It would eventually fade out after a while, but it takes a long time.

Honestly, in the past I have suffered some confusion regarding this sustain, release, and decay thing. (Attack always seemed pretty straightforward to me.) You may be a quicker learner than I am, but if you could use some further clarification, please try the following exercise, maintaining the settings from the previous exercise.
1. Set Attack and Sustain to zero.
2. Set Decay to 6o and Release to 81.
3. Depress and hold a key until the sound fades completely away; then let go. Even though your Release is set at a value of 81, you should not hear anything after letting go of the key.
4. Strike and let go of a key as quickly as possible. (lust quickly tap it.) If you do it right, you should hear the effect of your Release setting. The note will continue to fade out even though you have let it go.

Steps 3 and 4 work the way they do because the Release setting controls the amount of time it takes for the level of a sound to drop to zero from whatever level it was when you let go of a note. When you tap and release the note, it hasn't had time for the Decay portion of the envelope to finish. The note has not dropped back down to zero before you let go. So after you let go, the level will fall at a rate determined by the Release value. You could also turn the Decay setting all the way down, and turn the Sustain all the way up, and still hear the effect of your Release setting. For more information, see Using Reason's Virtual Instruments: Skill Pack.

This article is continued in Propellerhead Reason Subtractor Synth - Using Envelopes (Part 2).

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