Today I'll be demonstrating different amplitude envelopes on a synthesiser, so you can see how adjusting the attack time (A), decay time (D), sustain level (S) and release time (R) on a synth can make sounds which have different energy over time. We'll be looking at configuring synth patches that have switch, percussive, damped percussive, sustaining and quirk amplitude envelopes.
I'll be using the Gmedia ImpOSCar synth for today's demonstration, but any synth with a standard ADSR amplitude envelope will be able to create similar types of sounds.
Switch envelope
A switch envelope is used to recreate sounds that are only audible while a key is pressed - they begin when a note on event is received, and end when a note off event is received. Switch envelopes are typically used to create organ-style patches, for example the sound of a hammond organ where as soon as you release the key, the organ sound ends immediately.
I set up an organ-style patch in the imposcar synth with the following amp envelope settings:
D: very low
S: 100%
R: very low
With a patch like this, the sound will immediately fall to the sustain level when the key is pressed (note on), and when the key is released (note off) the sound will end straight away. Take a listen to the organ patch:
What did you hear? The organ notes have no decay or release and end abruptly on note off, just like a real organ. If you take a look at the waveform you can also see the lack of decay or release, and the notes start and end very abruptly.
Percussive envelope
A percussive envelope is used to create hit or plucked type sounds, such as drum hits (kick, snare, hi-hat) or pizzicato (plucked) type playing technique on a stringed instrument like guitar or violin. A percussive envelope has sustain and release set to zero, normally a very short attack time, and the decay time is used to set the length of the percussive hit or pluck.
I set up a kind of snare-style patch in the imposcar synth with the following amplitude envelope settings.
A: almost zeroD: around 0.5s
S: 0
R: almost zero
Take a listen to the patch and note the characteristics of the sound:
What did you notice? The sound is very percussive and decays over the specified decay time. With a patch like this, the note length is not affected by the sustain level or release time, and the sound will always be the same length unless the note length is shorter than the decay time. Take a look at the waveform and notice how the hits begin immediately and then decay quite quickly. Waveforms for other percussive style sounds like hi-hats and claps will look very similar.
Damped percussive envelope
A damped percussive envelope is used to recreate sounds of instruments like piano (where the notes are damped by the key dampers) or on guitar where strings can be damped by muting with the left or right hand.
A damped percussive envelope is similar to a percussive envelope except it will also have a release time set quite high - when the key is released the release part of the envelope will kick in, giving the sound a longer tail than strictly percussive sounds.
In the imposcar synth I set up an electric-piano style patch with the following amp envelope settings:
A: almost zeroD: around 0.5s
S: 0
R: around 1.5s
Take a listen to the patch:
How did it sound compared to the percussive patch? The damper percussive sound has a bit more of a natural tail as you can see by looking at the following waveform:
Instead of sounding like a drum hit, the sound has a piano-like characteristic as if the note is being damped by a key damper.
Sustaining (blown or bowed) envelope
To recreate the sound of a string or brass instrument, such as violin or trumpet, we can use a sustaining envelope. In this type of envelope the sound will have an initial attack and decay, fall to a specified sustain level while the note is held, and then fall to zero when the note is released.
I set up a string-style patch in the imposcar synth with the following settings:
A: around 0.6sD: around 4s
S: around 33%
R: around 1.5s
Take a listen to the patch and note the characteristics of the sound:
This sounds more like a bowed instrument than the other patches due to the sustaining envelope - while the note is held the sound falls to the sustain level, and when the note is released the sound fades out to zero. The sound also has a natural fade in because of the attack time. In this example the next note starts before the previous envelope has finished, creating a continuous sound as shown in the following waveform representation:
Quirk envelope
The last type of envelope we'll be looking at, is what Loudon calls a quirk envelope. This type of envelope has a very low attack, short decay time, 0 sustain level and very high release time. As the release phase starts on note off, if the note is released before the decay time ends it means the release part of the envelope takes effect. This can be useful to create sounds that have a very short percussive beginning and then long release time, not to model a real-world instrument but to create a different kind of sound.
I set up a patch with a quirk envelope in the imposcar synth, with these settings:
D: around 0.6s
S: 0
R: around 4s
As you can hear the sound has an extremely quick pluck at the beginning because of the extremely short note length I used to play back the patch, and a long release tail because of the release setting. Take a look at the waveform and you can kind of see this characteristic.
Conclusion
Today you've learned how using a synths amplitude envelope can be used to create sounds similar to real instruments, because of the nature of the envelopes. We saw how you can create organ style patches with a switch envelope, or percussive style hit or pluck patches with a percussive envelope. We then saw how you could create an electric piano style patch with a damped percussive envelope, a string style patch with a sustaining envelope, and we also looked at the quirk envelope.
I hope you've enjoyed reading and listening today and that having audio clips, waveforms and showing the envelope settings has demonstrated each type of envelope clearly for you. Feel free to leave any comments and let me know if any of my information is incorrect. Thanks for reading!
