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Envelope Generators: The shapers of sound.


In addition to sound having a pitch and a wave form sounds have shape and change over time. Envelope generators provide the means for shaping sound over time. Sounds have a birth, a life, and a death.
The birth portion of the sound is called the "attack and initial decay". This portion gives the sound much of it's characteristic. The ear uses the attack portion it know what a sound is. This initial portion is probably the most important because when we were evolving we needed to know if that sound was food, or something that wanted to make us food - so a quick ID of the sound was essential. For some sounds, mainly percussion, this is all there is. Velocity (how fast(hard)) and pitch (key number) can be used to change the length of the attack portion)
The life of the sound is the sustain; as long a key is held down the sound stays more or less the same. On the SQ-80 you can use the "second decay" as a slowly fading sustain (that would be most realistic on a plucked string) or don't use it and maintain a level sustain using the sustain level. Organs, winds, bowed strings have a more or less steady sustain. Other modulators can be used to add "life" to this generally steady sustain (See LFOs and also Other Modulators). The sustain starts after the attack/decay portion of the envelope completes, and remains as long as the key is held down (or held using the pedal).
The death of the sound is the release. After the key is released the sound starts to fade away,the sound starts to die. The way a sound dies is determined by the Release portion of the envelope generator. The SQ-80 has a second release that function somewhat like a "reverb" ... adding a bit of depth to the sound.
The envelope generators, and there are four on the SQ-80, can be used to modify any number of things. There are three properties of the sound that typically are controlled by an envelope: Amplitude or loudness by modulating one for the four Digital Controlled Amplifiers, Timber or tone "color" by modulating the Digital Controlled Filter, and pitch by modulating the DCO's.
The envelopes generally have a level and a time to get to that level. When the key is released the envelopes go right to the release stage and start on the way to zero. The table shows how long it takes to get to each level, assuming the values for TK=0 and T1V=0, and the key is held down long enough to run a complete "cycle". Non zero values of TK and T1V tend to make the times shown shorter. There are parameters on the modes page (VC, ENV, CYC) that can change the way envelopes function as well.
SQ80 EG PAGEEach of the 4 envelope pages (ENV1 - ENV4) have the following controls:

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