Audiomatic
Many types of sequencers and sequencing programs were used to place entire songs in a MIDI format on the 'internet', before the rise of MP3 encoding which replaced it. The problem with the MIDI, used in this way, was that synthesizers used for playback might be so radically different from the synthesizer(s) used to create it that one would hear only a jumble, or certainly nothing that the original artist intended.
But even when the MIDI is played on the desired equipment, and the tracks run through the desired filters, and the result saved in an audio format, even if it might be a compressed MP3, it is still mechanically generated. The emotion can be expressed. But the expression, and not referring to a technical control called, Expression, is different. A real instrument is manipulated in many subtle ways. Some instruments can be used in very different ways, a trumpet, or a muted trumpet. A stringed instrument is even more varied in what it can do. Classical guitarists, pop guitarists, pay thousands for just a particular sound on a particular instrument, and only then apply their unique styling.
Since all of that is beyond the realm of a computer generated performance, even one carefully tweaked over weeks and months, even one using some interesting filters which tend to suggest more the real performance than synthetic, I tend to see these as 'walkthroughs', even if I also think they tend to stand alone as finished. For the limitations just mentioned, it is still a performance after all. But as a 'walkthrough', it also calls to mind story boards or the like put in motion in preparation for final performance for a production film. These are animatics, or videomatics, or whatever they might be called, that have put together much of the work, the angles, the dialog, and such, but not the finished product. While these 'audiomatics' are closer to what might be a final live performance by comparison, I think the analogy isn't wrong.
Filters
The basic tones tended to be one synth earlier on. It just made it easier. But gradually, synths of all types were used. Sometimes sync/latency problems were had which made it necessary to record parts separately because they couldn't be played together without 'sliding' certain tracks to compensate. And it proved better to then also record the separate percussion tracks. And at that point, save for lacking the knowledge of experienced recording engineers, it wouldn't have been much different than a studio mix, except that no attention was paid to microphone placement and some other things (since the sounds were generated directly in the computer).
It also meant trying to find 'holes' for each instrument in the overall mix, emphasizing some EQ bands and de-emphasizing others, for each part. But filters served that purpose, too. Much of this is mentioned in the NOTE file found in the _EXTRAS_ directory of the Dive In CD. Two filters that proved useful for fitting everything into the final mix were Endorphin and IQ4. The latter was particularly good for bringing out certain tones. And both are free, as well.
The fuzz distorted guitar sound is approximated and features prominently in most every song on the Dive In CD. Hard rock, with the distant 'junk-blues' bass, Diddley, Berry, etc, still in the back of one's mind. AC/DC, even Guns n Roses, and so on. And it almost didn't matter what tones one began with, as long as some clean guitar were present in the 'layering', and some sense of harmonics and feedback, even finger slide scratching where appropriate. Because it all came out fairly the same on the other side of Voxengo's, Boogex, a guitar and cabinet reproduction filter; also another free filter. One that isn't free is the Free Filter, ironically named, from Steinberg. It's a quick way to match the frequency band of say, an actual distortion guitar from some other recording, to the collected and processed tones as used here.
Other filters helped with the distortion sound, and to help phasing. Sometimes it helped in the final mix, and phasing (slightly) not just the lead guitar. Other filters from the provider of Endorphin were often used. And again, various of these are mentioned in the NOTE file found in the _EXTRAS_ directory of the Dive In enhanced CD.
FInally, some of the expression, emotion, emphasis was initially added by running tracks, or parts of a track, through an older version of an Ntonyx.com 'performance modeling' program. Hundreds of controllers could be instantly and automatically added. And changes then further required could be added in by hand. But it tended to suggest a lot of the riffs finally used in various songs.