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Could you explain to me the difference between "decay" and "sustain" on synths? I'm using the Korg Kronos 2 and the synth engines have both sustain and decay and they seem to be doing the same thing unlike "release" for instance.

I'm thinking there isn't any difference, but could I be wrong?

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  • In Kronos, you are able to change the time and curvature of the decay and the level of the sustain.
    – Joseph K.
    Dec 26, 2017 at 3:00
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    You are possibly unable to hear the effect of Decay because Korg Kronos has a break level option that fits right between attack and sustain level. In Kronos, decay is the time between attack and break level, so it is not the typical time measurement between attack and sustain. If you are unable to hear the difference between decay and sustain, that is because of your slope time and break level. You can refer to my answer for more information and the link to the Kronos manual.
    – Joseph K.
    Dec 26, 2017 at 7:23
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    I feel like we have sufficiently covered all bases for your question. We would appreciate it if you can accept one of these responses as an answer once you are satisfied.
    – Joseph K.
    Dec 27, 2017 at 1:18
  • @JosephK. I would appreciate a visual answer though. However, Philip's answer is great.
    – SovereignSun
    Dec 27, 2017 at 4:35
  • No problem, I have added the picture of the curve in my answer.
    – Joseph K.
    Dec 27, 2017 at 4:42

2 Answers 2

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The ADSR envelope (and derivatives) is as follows:

A: Attack - the length of increase in voltage* (or analogue)

D: Decay - the length of decrease in voltage that comes after the increase

S: Sustain - the amount (or level) of voltage to sustain after the decrease

R: Release - the length of time it takes for the voltage to go back to 0.

Telling the difference between Decay and Sustain when using a volume envelope can be difficult as you will only be hearing the difference in loudness. I recommend, for experimentation purposes, using (or routing) the envelope on the low-pass filter. You will hear differences more clearly when you are listening to changes in timbre. You will then be able to play with the decay which will cause the sound to be plucky (that's my word and I'm going to stick with it) while playing with the sustain will cut short the pluckiness but have a steady sound come after you play a long note.

A high decay value means that pluckiness is drawn long. A low decay value means that it is going to be short. A high sustain means that the decay will not sweep through the whole range but get stuck at a higher timbre. A low sustain value means that the decay will sweep more until it stops.

This can be applied to other parameters as the synthesiser permits.

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    It might help to point out that one thing that makes sustain different from the others is that it's a level, while the others are lengths of time. You can easily hear the difference in different sustain levels by turning attack and decay way down, playing and holding a note, and then turning sustain up and down, since you will be changing the level of the parameter that is affected by the EG while the note is held, and you're holding the note.
    – Todd Wilcox
    Dec 23, 2017 at 21:58
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Kronos Synth has some advanced ADSR modeling features to tailor your sound.

enter image description here

Click here for the Kronos manual.

EGs (Envelope Generators)

The modeling section is divided into three parts: Level, Time, and Curve. All of these three components are defining a single curve, so when adjusting your sound, it is important that you check all three of them.

Also, due to these advanced options, it is possible to create an inverted ADSR curve shape, that is, an upside-down ADSR curve shape.

Level (In order of sequence):

  1. Start (0): Initial level at time 0
  2. Attack (A): Level to change to following the start level
  3. Break (B): Level to change to just before the sustain level
  4. Sustain (S): Level to sustain before the key is released

Time:

  • Attack: The length of time between the start level and the attack level. t(0)~t(A)
  • Decay: The length of time between the attack level and the break level. t(A)~t(B)
  • Slope: The length of time between the break level and the beginning of the sustain level t(B)~t(S)
  • Release: The length of time between the end of sustain level and the release falloff t(S)~End

Note: Take note that sustain time is not included as it is dependent on how long you hold the key. The length of sustain ends upon release of the key.

Curve:

I can't find detailed information on the curvatures available, but it appears that 0 is a linear curve and I am guessing that it gradually accentuates the S curve as the numbers get higher.

  • Attack, Decay, Slope, Release

Final Note: In Kronos, the levels and times are defined by values 00 ~ 99, which most likely are percentages of some given voltage and a time frame (ms).

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  • I like the 'common man' approach. But wouldn't a nail tapping have some attack? It's heard immediately, but for a very short moment. Looking at it on the vu meter shows action at the beginning. In fact, a vu meter seems to be a good way to explain. Not +1 yet.
    – Tim
    Dec 24, 2017 at 13:01
  • All you need is any synth to an ADSR EG to know that setting everything at zero produces no sound. Even a very short sound like nail tapping has some decay. When making drum sounds, finding the right amount of non-zero decay is critical. Actually, none of these make much sense to me. Better to list attack, decay, and release times in ms or seconds, and sustain amount as a percent of the unmodified voltage of the modulated parameter. What the heck does "25% decay" even mean? 25% of what?
    – Todd Wilcox
    Dec 25, 2017 at 11:23
  • Thank you all. I have changed my answer specifically for Korg Kronos.
    – Joseph K.
    Dec 25, 2017 at 18:12

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