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Why ADSR?

Submitted by on March 12, 2010 – 5:52 pm 2 Comments

One of the things that characterizes almost every synthesizer is it’s use of envelopes to control things like volume, filters and all sorts of other parameters. It doesn’t matter if it’s digital, analogue, additive, FM, subtractive, wavetable or a softsynth, it’ll usually employ some sort of envelope.

The reason for this is that most sounds change over time. This is especially true for ‘natural’ instruments that the first synthesizers were often used to emulate. Every instrument produces sound that changes in a way that is different for each instrument, creating a countour ‘signature’. The attack and the decay has a profound effect on the character of the sound, and therefore being able to control this (along with spectral content) is essential for emulating various instruments with a synthesizer.

By far the most common type of envelope that we see today is the ADSR (attack-decay-sustain-release) style envelope, which we can apply to volume, filter frequency cutoff, and many other parameters, often via a modulation matrix.

But where did the idea of an ADSR come from?

As early as 1938 (25 years before the first Moog), the Hammond Novachord used a 7-position switch to select different ADS (attack-decay-sustain) values, and also had a footpedal to control the release time, which created a sort of pseudo-ADSR envelope controller. It wasn’t until Vladimir Ussachevsky, the head of the Columbia-Princeton Electronic Music Center, started working with Bob Moog in 1965, and suggested to Moog that he use an ADSR envelope that it became part of synthesizer history.

You should definitely check out some of Vladimir’s film music here and here.

Since that day, almost every commercially successful synthesizer had some form of ADSR envelope to control at least the amplitude of the sound (I’m sure people will chime in here and tell me how I’m wrong). There have been a few variations, such as the Korg MS-20, which used a ADSHR (attack-decay-sustain-hold-release) envelope. By adding the “hold” parameter, the MS-20 allowed notes to be held at the sustain level for a fixed length of time before decaying.

Of course although many modern instruments often use more complicated envelope generators, the majority of them are based on the ADSR idea, just using extra stages. That being said, a lot of people are still big fans of the simplicity of ADSR envelopes.

Thanks to Tim for the idea.

SynthGear Tags

  • diy synth ADSR

2 Comments »

  • Glass says:

    Buchla had groups of AD/AR, but two could be combined into a single ADSR, so yeah :)

  • Jack Hertz says:

    Thanks! I just love learning about this kind of stuff. Envelopes are so important and often over looking. JMO, but ADSR is sufficient 90% of the time because they are simple and intuitive.

    FWIW, some of the early digital synths offered some nice variations and extensions on the ADSR model. The DX7 and DX9 envelopes had a rate and a level for each stage. Kawai’s K5 offered 6 stage envelopes that were ADSR with 2 extra release stages. The Casio CZ-101 had 8 stage envelopes that took the rate and level model even further.

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