The MIDI Page: Envelopes

by Todd Albertson

Come with me now as we enter and explore the fourth dimension for a bit. The fourth dimension we are told, is Time, and Time is what music is all about. Music exists in Time ONLY. Your radio station sells Time, and measures the value of music by giving it Time, or not. If you attempt to place music into some other dimension, like say, our more familiar and easier to understand third dimension, you may have a piece of paper with notes on it, or a CD with digitally stored magnetic patterns, but it is not MUSIC until we place it back into the fourth dimension, Time. This is the great mystery of much of our existence, for we DO perceive Time, but unlike the rest of our world we have NO ability to move through it at will, nor in fact, can we affect it at all. Consider that in the third dimension, which is space as we know it, we can move about freely. We come and go to work, we move from one place to another naturally, but moving from one time to another is the stuff of good Science Fiction! Time is harder for us to grasp, and harder to work through than just about any other aspect of living. It is Time that we are specifically concerned with in this month's discussion of ENVELOPES and it is Time that will trouble us. If you don't understand something, keep reading; I may be able to clear it up by the end of the article, but also, I may not!

Let's begin with the old standby, the ADSR Envelope. You have undoubtedly heard of this, and may even have a thorough under-standing of it, but that is the starting point. If you have been keeping up, you will recall that last month we made a simple repeating sweep by using the LFO to modulate the Filter/Resonance combination. The rate of sweep was controlled by the LFO rate. Likewise the depth of sweep was controlled by the LFO amplitude, or depth. Now we are going to explore how to do much nicer sweeps by modulating the Filter/Resonance combination with an Envelope. We will also see how Envelopes can be used to create more musical sounds, such as piano, strings, and all sorts of other instrument simulations.

Synthesizers and the musicians who play them are in many ways, prisoners of their past. Much of the terminology came from those early synths, and it is still helpful to refer back to the history of these things in order to explain them now.

ADSR stands for the original four parameters of synth Envelopes. "A" stands for "Attack." In early synths, this was a knob to control the rate at which a voltage went from zero to maximum. By modulating the VCA with the Envelope, the programmer could make the volume increase slowly or quickly.

"D" stands for "Decay." This was used to lower the voltage again, but ONLY to the LEVEL of the next parameter, "Sustain".

"S" stands for "Sustain". This was the level of voltage following "Decay", and this voltage would not change, until the player released the key being held.

"R" stands for "Release". This parameter controlled the rate at which the voltage would fall to zero after the release of the key.

These Envelope voltages could be applied to other modules of the synth such as the VCA, or the Filter/Resonance combo. The usual piano/plucked/struck configuration was a VERY short attack, a moderately quick decay, a medium sustain voltage, and a very fast release. If you think about the sound of a piano, this makes sense (here's something new!). A piano responds immediately to the force of the hammer striking the strings. There is no gradual build of sound, so it is a quick attack. The sound immediately begins to fade and change in timbre, even if the note is held (unlike an organ), so we would have to say that it "decays" at a moderate rate. It does not however, decay to nothing at all, at least not very fast, so we would not be remiss to say that it "sustains" a sound if the note is held. Once the note is released, the sound disappears rather fast, so we must also agree that it has a fast release time. Dissection of sounds is the life blood of synth programmers. If you wish to master this gear, you must learn to do this sort of analysis.

That was the easy part. Nowadays, we have lovely little problems called COMPLEX Envelopes! It sounds worse than it is. In some ways complex Envelopes have made life easier. All that has happened is that sound has been subdivided into smaller pieces, and "Time" has replaced "Rate." The Time/Rate substitution is a MAJOR improvement.

For the illustrations in the rest of this article, I will use the Ensoniq ESQ-l's complex Envelope. Do not worry if you are using a different synth. The ESQ's complex Envelope is-probably the best all around Envelope on the market today, and will easily show the features of most other synths. I regularly use this instrument to train new employees at Clean Sheets, Inc., and they never seem to have a problem switching into the other units once• they master this one.
This complex Envelope is really a convention adopted to make it EASIER for us to cope with a VERY sophisticated computer. Let's look at some new concepts:.

1) Everything is expressed in terms of numbers. ,There are no handy knobs to reach up and grab. You enter parametric values.

2) NEGATIVE numbers are allowed.

3) There are seven parameters. You will be able to control four Times, and three Levels.

4) In addition to these basic seven parameters, there are three special additional parameters controlling keyboard feel/velocity, which I will not cover. They would take too much space here.

Tl, or Time 1, is simply the TIME (not rate) to go from zero to 1,1, or Level 1. Now this is great! Set Level 1 wherever you want and then tell the synth how much time you want it to take to get there. If the value of Level 1 is raised, the synth will still get to that level in the same amount of time! You have probably already deduced that T2 is the amount of Time necessary for the signal to change from Level 1 to Level 2, and T3 is the time to change from Level 2 to Level 3. Be careful though... T4 is different. Since there is no fourth Level parameter, what could. this be for? You guessed it. T4 is the Release time. It is the parameter that tells the synth how long to take getting back to zero after the key is released.

You may be wondering what possible use there could be for negative numbers in an Envelope. Not much, if you think only in terms of volume, but if you apply that to a filter, or an LFO, or even the Oscillator itself (all possible, in the ESQ), this becomes a formidable tool. For instance, if Tl is set to zero, Level 1 is set to the maximum positive value, T2 is set to a moderately short time value, and 1,2 is set to the maximum negative value, and if this were modulating an oscillator, the sound would start with a high pitch, and rapidly move lower and lower until it reached the lowest note possible. This is the common "synthesizer ZAP" that you've been paying perfectly good money for up until now. Since the ESQ allows you to assign virtually any module to modulate any other module, you could double the affect by assigning one of the two REMAINING completely separate envelopes to do the same thing. What is more, you could assign them, or another, to modulate the Filter/Resonance combo at the same time! This flexibility is what modern complex Envelopes are all about.

Most modern synths are still not as flexible as the example used, but nearly all of them use envelopes similar to this. Unfortunately, many of the Japanese manufacturers insist on writing their owner's manuals in Japanese and then having them translated, or else having a Japanese author (who knows English) write them in English. You would be astonished at how badly these manuals are written! An American author would make things so much simpler, but these companies have been absolutely pig-headed about this. You, as the buyer, suffer terribly when you try to understand this junk! Of course, it's hard here, because I don't have two hundred and some pages at my " disposal, so I end up feeling like I skimmed over things that I wish I could cover in depth. I also must get on with the main thrust of this section, MIDI! Therefore, let me say this: The finest synth programming tutorial I know of is the ESQ manual. Whether or not you ever buy this instrument, I recommend you borrow a copy of this manual and read it cover to cover. Then, when you buy new a synthesizer (or try to figure out your old one), you will have far fewer problems.

I know these three introductory articles have been difficult, and if you've hung with me through them, let me take this moment to say, "Thanks." The rest gets a good deal easier. MIDI itself is our next topic. If you haven't managed to understand all this, don't worry, you will be fine anyway. It takes a lot of time to get good at this stuff. You were probably a real mess the first time you ever spliced tape too! If you have questions, you may write to me at R.A.P., or call my BBS (if you have a modem) and leave a message, 313-544-0405, 8pm-8am, nightly. Live long, and prosper.

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