ADSR

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The abbreviation ADSR stands for four phases of an envelope of a sound curve . This curve is generated by a so-called envelope generator, usually an electronic circuit or software. Ultimately, it is a time-varying control value (in the case of analog technology in the form of voltage and current curves or in digital applications in the form of discrete values) that acts on a volume control and i. d. Usually triggered by the keystroke of a keyboard.

definition

The letters are derived from the English terms:

  • A ttack (rise),
  • D ecay (waste),
  • S ustain (hold),
  • R elease.

This 4-step ADSR curve is by far the most widely used envelope shape. However, there are also forms with 5, 6 or 8 phases.

Use of ADSR

ADSR envelopes are used in audio synthesizers , among other things , to control the volume or timbre of tones. To do this, the envelope curve is applied to the control input of a voltage-controlled amplifier ( VCA ) or a voltage-controlled filter ( VCF ). The filter envelope is particularly popular in today's music, because it makes the sounds look more lively than with fixed filters. ADSRs can also be used to control other synthesizer modules. For example, the pitch of an oscillator ( VCO ) or the frequency of an LFO ( vibrato , tremolo ) can be controlled.

Parameters and phases of the envelope

ADSR phases

The envelope is given by 3 time and one amplitude parameters: attack time , decay time , sustain level and release time .

The four phases are as follows:

  • Pressing the button starts the attack phase . The attack time indicates the time in which the voltage increases from zero to its specified maximum.
  • The decay phase begins immediately after the maximum has been reached . The decay time defines the time in which the voltage drops from the maximum to the sustain level.
  • The Sustain level indicates how high the voltage is (as a percentage of the maximum) while the key is held. The sustain phase is only reached when the decay time has passed. If the key is released before the end of the decay phase, the release phase begins immediately (ADR process).
  • The release phase begins as soon as the key is released. The voltage drops from the sustain level to zero. The release time determines how long the sound lasts.

Long attack times result in a swelling sound (wind instruments, strings), short attack times a more percussive sound.

In analog synthesizers, the curves are usually not linear, since here a capacitor is charged or discharged via different resistors and the voltage determines the output value. In the attack phase the curve rises faster at the beginning, in the decay and release phase it falls faster at the beginning. The latter in particular contributes to a “more natural” sound when controlling a linear VCA, as it corresponds to the envelope curve of a damped oscillation .

Special cases and applications

If the sustain setting is 100 percent, the decay phase (ASR curve) is practically eliminated. A typical example is the timbre of a string instrument . A sustain level of zero percent suppresses the sustain phase (AD curve). A typical example is the volume curve on a guitar . With organ tones again a course is almost on without attack or release, as the sound during the keystroke is present almost equally and apart from reverb section has no aftertaste. The full ADSR envelope is z. B. needed to model the volume curve of the piano during sostenuto (attack) and the use of the forte pedal (sustain + decay).

A variant of the envelope only takes into account the stroke of the key, not the release. Then there are only the Attack and Decay phases (AD progression). A typical example are instruments like the vibraphone .

Depending on the manufacturer and instrument, there are numerous variants in addition to the common ADSR envelope, ranging from simple AD versions (attack decay), such as the Roland TB-303 , to complex versions with up to eight elements, e.g. B. in the Casio CZ series.
Further parameters can e.g. B. Reattack or Hold. In the hold phase, the maximum value reached after the attack is held for an adjustable (usually very short) time, which can give percussive sounds more pressure.

Operators for ADSR groups

In natural sounds, each partial has its own envelope curve. As a rule, the higher their frequency, the faster the partial tones decay, because the energy attenuation is proportional to the frequency. With additive sound synthesis, this can be imitated by assigning each oscillator (= partial tone) its own envelope. So that the setting of the many (8-16) ADSR generators is not too time-consuming, they are processed by operators in groups. So an operator can e.g. B. ensure that the attack times are shortened with increasing pitch, which leads to a very distinctive note attack. Other operators can control the decay and release times or the level depending on the pitch. You can also pick out individual overtones and give them an individual envelope, which leads to a rich play of timbres.

Dynamic ADSR generators

The classic envelope generators use fixed times for the attack, decay and release values. As a result, long notes are simply cut off with short strikes. With dynamic envelopes, the attack and decay times are adapted to the duration of the sound. This leads to a more dynamic sound. This only works with synthesizers that are played using midi files, because the duration of the tone must be known before the envelope starts.

Alternative forms of ADSR

The company E-mu Systems used 6 phases as standard in their sound generators. In addition to times, further amplitude threshold values ​​were specified in the attack and decay phase, which automatically transferred to the next phase when they were reached. Thus, a more dynamic course could be specified.

See also

literature

  • Rolf Beckmann: Manual of PA technology. Basics, components, practice. 2nd Edition. Elektor-Verlag, Aachen 1990, ISBN 3-921608-66-X .
  • Roland Enders: The home recording manual. The way to optimal recordings. 3rd, revised edition, revised by Andreas Schulz. Carstensen, Munich 2003, ISBN 3-910098-25-8 .
  • Thomas Görne: Sound engineering. Fachbuchverlag Leipzig in Carl Hanser Verlag, Munich et al. 2006, ISBN 3-446-40198-9 .
  • Synthesizer Workstation Pro. the music laboratory for your PC. Franzis-Verlag , Poing near Munich 2010, ISBN 978-3-645-70094-8 .

Web links

Commons : Envelopes  - collection of images, videos and audio files

source

  1. Music Producer Home Studio, Avanquest Verlag Munich, EAN 4023126111647.