You're probably not looking after technical details about sound file formats, and in anyway you won't find them here (for this kind of information you might want to go to Harmony central which will tell you a lot of things about MIDI data structures and programmation, for instance).
But you're indeed reading the right page if you're a little bit confused about all these file formats, and wondering why there are so many of them. Thus, I'll try to give here a few basic principles that I've found useful for my personal usage.

Driving a synthetiser or an electronic piano from the computer, or, conversely, sending to it, in a score editor, notes played on a keyboard... how are these miracles possible? They are because the computer and the sound device - which might be a basic soundcard - agree on some method to talk to each other by exchanging a set of commands known as MIDI standard.
Each event involves such a command labelled by a number; often some more data is added after the command in order to describe precisely what should be done. Thus, the beginning of a note is specified by some command followed by a number giving its pitch. Other commands specify the end of a note, its loudness, the amount of reverberation, etc.

Changing the program or patch is quite a remarkable event that specifies which instrument must be heard. By what will this instrument be played? By hardware and software installed at your home: soundcard and its drivers, synthetiser... That's why performances might sound quite differently, depending on the configuration, because each device holds its own sound samples, which were made more or less carefully, thus making each instrument sound with more or less truth, loudness, softness, etc.
And we're quite lucky, because General MIDI standard once put an end to a great cacophony: some time ago, sound devices were agreeing on basic MIDI commands, but not on instrument numbers; hence you could send a violin patch command, for instance, and ignore that some people were hearing a saxophone! Such proprietary instrument numberings still continue to exist - I don't know why - but, at least, everybody seems to agree to support this General MIDI mapping which insures a minimum of compatibility between various configurations.

Now, how is it possible that we hear different instruments at the same time? Well, first of all, because hardware allows that, like it does for some powerful multi-processor computers. Secondly, each of these playing modules is labelled by a chanel number. Most commands, like changing the instrument patch, are thus supplemented with the chanel number to which they must be sent; that's why one can change not only the instrument program, but also its loudness, its position in space, ... ; and this can be done for each chanel independantly.

To summarize about this first file format, two things must be emphasized:

• playing a MIDI file is not reproducing a performance, it's a new performance;
• such a file made of command numbers is quite small: a few thousands or dozens of thousands of bytes.
That's why it's so popular on the net, since it can be downloaded very quickly.

WAV files are nearly as old as micro-computers, but they seem to become up-to-date again, for several reasons:

• some subtle details remain beyond the purpose of MIDI standard; WAV file format can reproduce them;
• the most recent soundcards allow to personnalize instrument patches; this dramatic improvement has its drawback however: it makes still more difficult to compare performances heard on various configurations;
• WAV format is a step in the process of creating an MP3 file which appeared recently and that we'll describe later.

The MP3 algorythm is an approximative compression technology, which allows to reduce WAV file sizes by a factor of 4 to 40 roughly.

Generally speaking, two main classes of compression techniques may be considered:

• An exact compression takes in account data redundancy; it's moderately efficient, but it can rebuild exactly the original data when uncompressing; this is necessary for some computer data files containing texts or programs, for instance. Let's imagine we're compressing this page; we would memorize once only the word soundfonts labelled by some number like 14 - why not - and then refer to it several times and save some space in the file; later on, the uncompressing program will rebuild the original text from the only instance of the expression memorized in the compressed file.
• An approximative compression is able to extract that part of data which is responsible for the most important part of the expected result. That is, we accept some loss of picture or sound quality, in exchange of saving a lot of space. The most versatile techniques allow to choose the compression ratio, and therefore the balance between size and quality. It's remarkable that such compressions are possible, but it must be said that they involve advanced mathematical techniques, applied to specific types of data. MP3 is just one of these techniques, relevant to sound files. Real audio is another one, which performs a higher compression but with a greater loss of quality. Such techniques are also available for pictures, resulting, for example, in JPEG file format, well known on the net.

Better ones can dramatically improve a MIDI performance, if you accept to do some more work on the files: articulations and note velocities obtained with great effort under a given soundfont set won't be relevant anymore under another set, since the latter will show, most often, quite a different instrumental balance, and different reberveration rates, etc.
We could share our comments about a performance if I'd publish here all the fonts that were used for each file, but this would be rather boring and would lead to a few problems:

• before making soundfonts available for download, I'd have to get each author's agreement;
• I'd hardly be able to give soundfont names: they are are often quite obscure, and for this reason I changed many of them and forgot the original names;
• last, soundfonts must match your soundcard, which I don't know (mine is SB Live).

The AudioHQ - Soundfont dialog box allows to load soundfonts into memory, up to a total size of 64 Mb.
Thus, each instrument patch, numbered from 0 to 127, can be personalized. A set of fonts with a patch for each of the instruments in the General MIDI mapping is called a sound bank.
Obviously, the better are the patches, the larger they are, and thus the same for the bank itself. To help us in finding a size-quality balance fitting our taste and hardware constraints, the card soft provides three factory banks of sizes 2, 4, and 8 Mb. They can't give an excellent sound for each instrument, but, at least, they let us start with an instrument patch for each number in the General MIDI table.

• You'll hear a difference every time you'll load a different instrument in bank 000;
• But, if you can't edit the MIDI file, you won't be able to switch to a different bank;
• To switch to another bank, you'll have to insert commands in the MIDI file.

Under this score editor, banks will appear as devices in the Staff sheet window!
Let's open this window, then click on the Program name column, and open the Device list; it displays several device maps: Generic, General Midi, Roland MT32, Kawai K1, etc. Let's learn a little more about this list, by having a look at the Devices directory under your Encore installation path (that is C:\Encore\Devices for most of you). Find, then open the Devices.ini file, it will look like that :

[DEVICES]
0=Generic
1=General MIDI
2=Generic 8x8
3=Roland MT32
4=Kawai K1
...
19=NOT_IN_USE
20=NOT_IN_USE

These devices are those appearing when opening the list in the Staff sheet window. By the way, if you're never using Roland MT32 and a few others, you can make this list smaller by replacing some the corresponding lines with this:

3=NOT_IN_USE
4=NOT_IN_USE
...

And now, what about the numbers at the beginning of each line? Each of them refers to one of the files Dev0.ini, Dev1.ini, ... in the Devices directory. Such a file describes a mapping that will be shown in the Staff sheet window when choosing this device. If you open Dev1.ini, for example, you'll see the quite familiar General MIDI table:

[DEVICE] TITLE=General MIDI
ABBREVIATION=MIDI
0=NONE
1=Grand Piano
2=Bright Grand
3=Elect Grand
4=Honky Tonk
5=Rhodes
6=Chorus Piano
7=Harpsichord
...

Installing a bank in Encore

Now, how will we install that Jeu d'orgues soundfount, assuming that we've loaded it as bank 1, for example? Well, I'll just tell you how I did that (I don't pretend I've discovered all that can be done):

I save the original Devices.ini, then I edit it: finding the first line with NOT_IN_USE for which no corresponding Dev.ini file exists in the directory, I write into it the name of the new bank:

[DEVICES]
0=Generic
1=General MIDI
2=Generic 8x8
3=NOT_IN_USE
...
10=NOT_IN_USE
11=Jeux d'orgues
12=NOT_IN_USE
...
19=NOT_IN_USE
20=NOT_IN_USE

Now we have still to create the Dev11.ini file, by looking at the instruments available for the Jeux d'orgues soundfont in the AudioHQ - Soundfont dialog:

[DEVICE]
TITLE=Jeux d'orgues
ABBREVIATION=jeux_1_2
0=None
1=Montre 8
2=Prestant 4
3=Doublette 2
4=Montre 8 Prestant 4
5=Principal (g.o.) 8+4+2
...
59=Gedackt 8+4
60=60
...
127=127
128=128

I guess you know what will happen now when we'll open the Devices list in the Staff sheet window: we'll be able to choose the Jeux d'orgues device (!); this will show its mapping table, and we'll be able to change the jeu exactly the same way we're used to change an instrument! Beware, don't forget that this will work only if we haven't forgotten to insert a swich to bank 1 command at the beginning of the file...