
It's extremely inportant to understand the function of the volume envelope. Before we can continue, we should check out the idea of the sustain phase. It's length on the graph is merely figurative. Actually it can last for ever, because the sound stays in that phase as long as a key is pressed i.e. a note is played. The sound is said to be looped. Looped sounds are not suitable to everything. For example a piano sound must die away after a key is hit also in that case the key remains pressed. Looping is clearly usable with those instruments whose sound is quite stable.
Now it is clear that there are two fundamental types of the synthesized sound. Sustained (e.g. looped) and non-sustained. We can forget the sustain phase for a little while and check out the attack, hold and decay phases. They can be used for both the looped and non-looped sounds.
The attack phase rises the volume from zero to the hold level. The length of the attack phase corresponds to the time spend in that phase. If you take away all the other phases, e.g. set their values to minimum, you have the attack left. If it's also minimized, you can't hear anything. The synthesizer plays the sound but we can not hear it because all the phases are at zero. Note that the length of the sustain phase stays all the time same, only the vertical position of it, i.e. the level drops to zero.
In our studies we use mainly the new Vienna SF Editor 2.0. From this point forward, I call the versions Vienna1 and Vienna2 . I also use Vienna as a general name when the context doesn't suppose the version number.
As discussed earlier SoundFont banks are hierarcical structures where individual samples can be arranged to form instruments and then those instruments to form presets for whole banks. These banks can then be used with a soundcard that supports them. The picture below shows the 'Sound Font Three' view. It is the main navigating tool in Vienna2.
A soundfont bank consists of tree parts: the Sample section, the Instrument Pool and the Preset section. The Instrument Pool could be named also a section, but because it has no subdivisions they call it simply a pool.
The Sample section is divided to User Sample Pool and ROM Sample Pool. The Preset section is divided to Melodic Pool and Percussive Pool. This article is not intended to be a guide to use every special finess or trick in Vienna. My goal is to give the mainlines for understanding the way computers do music. That's why we go straigth to examine a sound, violin sound. In order to do that we need to open an existing bank where we have that violin sound. We can use the synthgm.sf2 bank that comes with Vienna2. When the bank is open, the violin sound can be found from the Instrument Pool. When the folder is open, all instruments of this GM-bank can be seen in their standard order. Violin sound is #41 in GM-bank, so it resides approximately one third from the beginning of the list downwards.
The volume of a sound depends on how it was recorded and how the record was manipulated before using it in a soundbank. In the bank we can't amplify it more, althoug it is possible to attenuate it with the volume slider in the 'MIDI Controller Bar' which comes visible in the top part of the main interface when an instrument is selected. A full position of this slider corresponds to the original volume. For violin sound it is set to 100, a small attenuation to the maximum value 127. This control is used for balancing all the instruments in the bank so that they will have the same sensational volume level. This level is heard during the hold phase of the volume envelope.
When an instrument in the 'Three view' is double-clicked it expands to show the different samples used within that instrument. A synthetizer lowers and rises the pitch of a sample by playing it with slower or higher speed, thus making it sound unnatural if the process is too aggressive. That's why the maximum note range of an instrument is usually divided into zones, each using a sample recorded in a pitch within that zone. These zones can be seen in the Key/Vlocity/Range view to the right of Three view. The zones are shown with horizontal lines.
For example the 'arcoviolingx2' sample is used for keys that range from the lowest key on the keyboard to the A#4-note. Middle C (In Vienna C4 but usually C3 in sequencer programs) is marked with a small black rectangle. Next zone is very narrow - from B4 to D5 (that's tree halsteps or semitones). The sample used for this zone is named 'arcoviolinc3'. You can experiment with these sounds by pushing keyboard with your mouse. The timbre of different samples varies quite much. Note that there is a paino sample (kpianob5) used in the highest zone. This demonstrates nicely the idea of SoundFonts althoug the pitch is so high that it's very hard to hear. (There is also a design error in the 'arcoviolinc4' sample. Pitch modulation - vibrato - is too large and the sample starts to play wrong at few highest notes of it's zone.)
Before continuing, we must check out few other things which are of big importance in understanding how the envelope operates. I beg a pardon for this jumping from things to others, but there is so many separate subjects, that need to be known before we can see the process in it's entirety. Be patient, please.
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