5. Pushing the Envelope

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5. Pushing the Envelope Empty 5. Pushing the Envelope

Post  James on Tue Jun 15, 2010 3:45 am

“Envelope” is an audio term that I only had a vague understanding of for a long time.
It comes up on just about every synth and software instrument. This is the same basic concept behind the Attack/Hold/Release controls on compressors and gates.

Think of the “envelope” of a signal as a volume profile over time. It generally consists of four stages: Attack, Decay, Sustain, & Release.

Attack is the time it takes to hit peak volume after a note is hit.
Decay is the time it takes for the initial volume spike to subside.
Sustain is the time the sound rings out while a note is held (after the Attack and Decay).
Release is the time the sound rings out after the note is released.

This is a really simple, yet easy to overlook, way to mold a software instrument to your needs. You can stretch the attack of a piano to make it softer and less percussive. You can stretch the decay to make the initial volume spike last longer, making the piano hit harder. You can stretch the sustain to make it sound more legato. If you go nuts with the attack, you can make just about any instrument into a pad.

Longer attack times can be used to fake a “backwards” sound. Normal, forwards sounds usually have a volume spike, follow by a trail of sustain. Stretching out the attack put the trail in front. This works especially well on drums because drum hits don’t have trails of sustain behind them. When a long attack is added, they seem to stop abruptly.

You can also use gates to manipulate the envelope of a signal, instead of just chopping it up. The Attack/Hold/Release controls function pretty similarly to the ADSR on a synth. Hold is essentially the same as decay. (There’s no parallel for “sustain” because there’s no MIDI note being held.)

Envelope filters (aka. envelope-following filters or auto-wahs) work of this idea as well. They’re called envelope-following filters because they are filters that respond to the envelope of the audio coming into them. They’re like wah-wah’s, but instead of the frequency of the filter being controlled by a foot, it’s controlled by the level of the incoming signal.
James
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5. Pushing the Envelope Empty Re: 5. Pushing the Envelope

Post  James on Tue Jun 15, 2010 8:21 pm

The backwards sounding drums on Superhappyrainedbowland are just gated to sound that way. Nothing backwards there.
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