It is very difficult and time consuming, but it is possible. You need to have a great deal of source material so that you can induce the sort of randomness inherent in a real performance. I have found that programming a sampler is better than attempting it as multiple tracks in a DAW.

1. Even when perfectly tuned a real guitar does not retain its perfect pitch in performance due to the intonation of the instrument and the players finger pressure on the frets, making the tonality of the fretted strings slightly sharp. In loud passages the guitar will naturally be sharper as the player exerts more pressure on the neck and hits the strings harder with the pick.

2. Remember to arpeggiate the chords and don't forget to use down and up strokes. Up strokes are usually softer than down strokes. The beginning of the strokes are, most of the time, slightly ahead of the beat with the last note of the chord on the first beat of the measure unless the part is sitting way back in the groove.

3. A real performance does not always use all six strings. Some strings will be muted, but the muted strings will still be "heard" and will affect the overall sound of the chord.

4. There are always some string squeaks, slides and finger noises when transitioning from chord to chord.

5. Occasionally all of the strings are muted where the chord isn't sounded but the player propels the groove with that “chucka-chucka” sound.

The “secret” is to think like a guitarist. I learned by programming “cover” songs and trying, badly, to play some guitar. Knowledge of how instruments behave is essential to creating a realistic track. With B-flat instruments, B-natural and E-natural are slightly sharp, and C-sharp and F-sharp are slightly flat. As a performance goes on the string section of an orchestra tends to play sharper and sharper as the players are “deafened” by the brass section behind them. The brass section tends to get slightly flatter as the instruments heat up and expand during the performance.

There was a studio in L.A., I forget the name, that actually had a sampler for each violin, viola, cello and bass in an orchestra. Each one had a different sample set and the sequenced performances were randomized to create the effect of multiple players in a real orchestral string section. Whether you know it or not you have probably heard the results in the scores of many films released during the 90's.

Have fun and good luck!!!

thanks alot that was all really helpful! Excuse my ignorance, im only 16 so i've only been doing all this for a year or so, but when you say 'arpeggiate' the chords does that mean just spread them out slightly or do i have to use an actual arpeggiator to do something??
Oh yeah and seeing as it is so difficult could you recommend better option or do you just have to grit your teeth and get on with it lol?

An arpeggio is a chord with the notes in played in succession. A guitar strum is, in essence, a very fast arpeggio, although it does not really sound like one. I usually step record a strum as an arpeggio, randomize or humanize it, and then time compress the arpeggio until it sounds like a guitar strum. Make sure that all of the notes are extended until the attack of the next strum. Leave a small hole for transitions from chord to chord which you can fill with fret noises, etc. as described in my previous post.

When I was a performer I played keyboards. I spent a lot of time on the patches for my sampler and in the blare of a live situation the results were acceptable, especially when I played electric guitar parts through a guitar amp. A buddy of mine suggested plugging a mic into the guitar amp and raising the volume of the mic to near feedback levels to increase the harmonic content, which worked very nicely, since the mic took the place of the guitars pick-up. Adjusting tunings of other instruments as I previously described also added realism. On occasion band members were asked, “who was playing the sax?”, which was the ultimate compliment.

For guitar parts in the studio I just played each individual chord (anyone can hold a chord and strum) and attempted the transition to the next chord, doing multiple takes, and then I comped it all together. It wasn’t great, but did very nicely for demos. Before using DAWs I loaded these pieces into a sampler and sequenced them. Pro Tools and Digital Performer allowed me to do great crossfades, so the results were much more satisfactory. Once my demo was completed I had real players come in and perform for me. I bartered that kind of thing; get a band to play one of my tunes and then track one of theirs. That actually built the clientele for my studio when I was recording music (I now do sound design and music editing for film and TV).

At 16 I doubt you are coming up against hard deadlines with cash paying clients, so take some time and do it the hard way. It’s an education in itself.

Good luck and, most of all, have fun.

for acoustic guitar try "real guitar" by musiclab. sounds great for both picked and strummed guitar tracks.
i think there's a demo on their website.

greets

you should try Liquid Guitar by EastWest, because I think it is what you are searching for... :)