Consider some thought experiments:
Consider a situation where you, due to budget limits, can only hire 8 violinists to record your project, yet you wish to have the sound of 16 violins in the 1st violins section. So, you record the whole piece with the 8 violins, then have them move over to where the other 8 musicians would have sat, and record another pass. Is it not true that the sound of the 8 musicians tracked twice is in theory identical to the sound of 16 musicians tracked once?
Consider a situation where you have three trombone parts (divisi), but can only find one trombonist. So, you track the piece three times, with the trombonist moving over one seat for each take. It is only logical that the result is timbrally the same as having three trombones. So, we must conclude, if you were to use three different solo patches, pan them out so they are not seated identically (if not done already), and have each play a voice in a chord, it will sound like a section of three playing divisi.
For a real life proof of that, here's a (rough) multi-track I did a while back of myself playing 5 different baritone parts, moving around room with each take to pan the instruments around, then applying some hall reverb in the end:
https://www.dropbox.com/s/1l0flw9vyhcan8...s.wav?dl=0
(excuse the messy high part!)
For a virtual proof, here's two oboe d'amore, cor anglais, and baritone sax playing a piece virtually, panned around:
https://www.dropbox.com/s/s6kbz9x5hw8088...x.mp3?dl=0
I think we can all agree it would be funny to say that it sounds like there is only one instrument playing all of those lines, or even only one oboe d'amore playing two notes at once.
If you were to have six musicians in a section (say, six horns) and have 3 sets of 2 musicians each playing a note of a chord, you would get a different sound from having the 6 musicians all play the same note with 3 takes. After all, if we wanted to do 6 musicians to a note in a single take, we would need 18 musicians, or do 3 passes with 6 musicians. So, logically we must conclude that the argument is correct: if you take a patch with 6 musicians and play two notes on it at the same time, it is the sound of 12 musicians; 6 playing one note, 6 playing the other. Long ago I used to regularly load up a 6-horn patch and lay down 4-6 notes on it at once. It's a cool sound, but it's acoustically 'mythical' in character, requiring 24-36 horn players or 4-6 passes with a 6-horn section in unison to replicate in real life, a completely different sound than 4-6 solo horns playing divisi. It's good to use a library that has, say, solo, 2-horn, and 4-horn patches available, so that you can select the right one for the context.
Perhaps the issue with your solo observation comes from not panning other voices, or not using alternative solo instruments (if available). Using the same patch, the same takes, with the same placement in the stereo image, especially sans vibrato and if the samples are phase locked or mono, will result in a sound not so different from a solo violin doing a double- or triple-stop. Even having one use a vibrato patch and the other a non-vibrato patch should resolve this, or ensuring that the vibrato is at different rates, but for best results, a different performer entirely, sitting in a different position, should be used (if available). Of course for most instruments, only a single note is possible at a time, so it is harder for the brain to be convinced there is only one musician playing two notes on their magical oboe.
Consider a situation where you, due to budget limits, can only hire 8 violinists to record your project, yet you wish to have the sound of 16 violins in the 1st violins section. So, you record the whole piece with the 8 violins, then have them move over to where the other 8 musicians would have sat, and record another pass. Is it not true that the sound of the 8 musicians tracked twice is in theory identical to the sound of 16 musicians tracked once?
Consider a situation where you have three trombone parts (divisi), but can only find one trombonist. So, you track the piece three times, with the trombonist moving over one seat for each take. It is only logical that the result is timbrally the same as having three trombones. So, we must conclude, if you were to use three different solo patches, pan them out so they are not seated identically (if not done already), and have each play a voice in a chord, it will sound like a section of three playing divisi.
For a real life proof of that, here's a (rough) multi-track I did a while back of myself playing 5 different baritone parts, moving around room with each take to pan the instruments around, then applying some hall reverb in the end:
https://www.dropbox.com/s/1l0flw9vyhcan8...s.wav?dl=0
(excuse the messy high part!)
For a virtual proof, here's two oboe d'amore, cor anglais, and baritone sax playing a piece virtually, panned around:
https://www.dropbox.com/s/s6kbz9x5hw8088...x.mp3?dl=0
I think we can all agree it would be funny to say that it sounds like there is only one instrument playing all of those lines, or even only one oboe d'amore playing two notes at once.
If you were to have six musicians in a section (say, six horns) and have 3 sets of 2 musicians each playing a note of a chord, you would get a different sound from having the 6 musicians all play the same note with 3 takes. After all, if we wanted to do 6 musicians to a note in a single take, we would need 18 musicians, or do 3 passes with 6 musicians. So, logically we must conclude that the argument is correct: if you take a patch with 6 musicians and play two notes on it at the same time, it is the sound of 12 musicians; 6 playing one note, 6 playing the other. Long ago I used to regularly load up a 6-horn patch and lay down 4-6 notes on it at once. It's a cool sound, but it's acoustically 'mythical' in character, requiring 24-36 horn players or 4-6 passes with a 6-horn section in unison to replicate in real life, a completely different sound than 4-6 solo horns playing divisi. It's good to use a library that has, say, solo, 2-horn, and 4-horn patches available, so that you can select the right one for the context.
Perhaps the issue with your solo observation comes from not panning other voices, or not using alternative solo instruments (if available). Using the same patch, the same takes, with the same placement in the stereo image, especially sans vibrato and if the samples are phase locked or mono, will result in a sound not so different from a solo violin doing a double- or triple-stop. Even having one use a vibrato patch and the other a non-vibrato patch should resolve this, or ensuring that the vibrato is at different rates, but for best results, a different performer entirely, sitting in a different position, should be used (if available). Of course for most instruments, only a single note is possible at a time, so it is harder for the brain to be convinced there is only one musician playing two notes on their magical oboe.
Sample library developer, composer, and amateur organologist at Versilian Studios.