Understanding envelopes

In this tutorial, I’ll introduce you to the concept of envelopes. We’ll see how different envelopes look like, and how they sound.

Start with a fresh project (or track) on your DAW. Load Clearsynth and s(M)exoscope on the track. Load the “saw” preset in Clearsynth. Remember, in the previous tutorial, we modified the s(M)exoscope’s parameter to see the detailed waveform? This time we are going to leave it at the defaults. Play a short note and observe the waveform. It’ll look something like this.

Image 1: A short note with the saw preset

Try this again. This time, press and hold the note for a longer time. You’ll see something like this.

Image 2: A longer note with the saw preset

There are a few observations that are common in these two waveforms.

1. When you press a key, the volume increases from zero to a particular value.

2. From this value, the volume then immediately decays down to another value.

3. This value will now continue to sustain for the duration of time that you hold the key down.

4. When you release the key, the volume fades down to zero.

Every sound that you hear has some volume pattern like this, and it draws up such shapes when you view it on s(M)exoscope. Some are similar to what you just saw. Some are drastically different.

See how a kick drum looks.

Image 3: A kick drum

Notice how it goes from zero to maximum in an instant. However, from maximum, it immediately starts decaying its volume to zero. Also note how the volume does not sustain. A kick is supposed to be a one-shot sound. So, no matter how long you hold the key, the length of the sound does not increase.

Let’s look at a slow string sample now.

Image 4: Slow strings

As you can guess from the nature of the sound, this one starts very slowly. But it doesn’t seem to decay to a lower value. The sustain part is prominent, as you’d expect. You’d want the string sounds to be heard distinctly as you press and hold the key. There are lots of changes in volume during the sustain period. But essentially, the average volume is the same. Once you release the key, the fade out to zero is also quite slow.

In all these cases, what you’ve been observing is called the “volume envelope”. It’s the behavior of volume, and its changes over the lifetime of a single note of sound. As I said before, every sound has such an envelope. In the synthesis world, this is broken down to four parts in order to understand and control it.

The parts are the same 4 observations we made above.

1. The part where the volume goes up from zero to maximum as soon as you press the key. This is called the attack phase.

2. The part where the volume decays down from the maximum to a new volume level. This part is called the decay phase.

3. The part where a constant volume sustains throughout the duration of the key press. This part is called the sustain phase.

4. The part when the key is released, and the volume goes back to zero. This is called the release phase.

We can control the volume envelope of the sounds that we generate in synths by controlling these four parameters. Note that this is just one way of controlling volume envelopes. Some synths provide more finer controls, but these four controls will most probably be there anyway. This type of envelope is called the ADSR envelope (The letters stand for the names of each phase of the envelope).

Image 5: Standard ADSR envelope

This is the envelope control used in Clearsynth. See if you can identify these phases in the sound Clearsynth makes (or in Image 1 of this tutorial).

In our next tutorial, we’ll see how to control these four parameters to shape our sound.


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