There fore sustain on a guitar string is literally impossible without some sort of electronic enhancement.

1. Bolt on neck vs. set neck. Given 2 guitar bodies of the same design but one with a bolt on neck and the other with a set neck, the set neck will have a longer period of decay. This is because of the ability of a set neck to transmit sound waves better than a bolt on neck.

2. Hard tail bridge vs. tremolo bridge. Given 2 Fender stratocasters one with a the standard Fender tremolo bridge and the other with a hard tail bridge, the hard tail bridge will have a longer period of decay for the same reason as above.

3. The more mass at the headstock is another known contributing factor to create a longer decay.

4. The type of wood used in the guitar body construction is another factor. Hard woods will allow for a longer decay time than softer woods, e.g. Mahogany vs. basswood. This is because sound waves will travel faster as the density of wood increases which allows for better wave transmission. NOTE: most electric guitars may use many types of wood in their construction. Consider a Les Paul with a mahogany body, and a maple top, and an ebony fingerboard.

5. Heavier gauge strings will decay slower than light gauge strings as mass plays important role on wave transmission as well.

6. The nut and bridge material is also a factor. Again the density of the materials is significant. Consider the better wave transmission of graphite saddles vs. nickle.

Generally speaking a PRS guitar like the one Carlos Santana uses is optimized for his long 'sustained' notes, but that's only half the story, you should also see what pedals and tube amp he is using too.

http://www.prsguitars.com/santana/

http://www.uberproaudio.com/who-plays-what/126-carlos-santana-guitar-gear-rig-and-equipment

Beyond the acoustic factors listed above, we should now examine the pick ups and the amplifier. There are a zillion pick ups out there, both single and dual coil (aka humbuckers) pick ups will vary on how the sound is transmitted to the amp and this will have an apparent influence on the decay time. The settings on the amp and the amp build may have an influence as well. Foot pedals aimed at increasing gain and compression are factors too. Consider SRV playing a strat through a tube screamer then into a vintage Fender Super Reverb with optimal NOS tubes, and a mix of AlNiCo and Ceramic speaker magnets. Plenty of sustain.

 http://www.uberproaudio.com/who-plays-what/162-stevie-ray-vaughan-guitar-gear-rig-and-equipment

Aside from using a "sustain effect processor" one could use any of the following to create sustain:

a) Ebow (http://en.wikipedia.org/wiki/EBow)

b) Old school controlled amp sustained feedback e.g.

c) Use a real bow on a guitar with violin strings and an arched bridge.

d) Post production using a DAW. Record your piece, copy and splice the waves on and on together.

e) Loop the sound in an effects box.

Here's a website that discusses real vs fake sustain: http://www.sustainiac.com/aboutsus.htm

Therefore, sustain on a guitar string is literally impossible without some sort of electronic enhancement.

1. Bolt on neck vs. set neck. Given two guitar bodies of the same design but one with a bolt on neck and the other with a set neck, the set neck will have a longer period of decay. This is because of the ability of a set neck to transmit sound waves better than a bolt on neck.

2. Hard tail bridge vs. tremolo bridge. Given two Fender Stratocasters, one with a the standard Fender tremolo bridge and the other with a hard tail bridge, the hard tail bridge will have a longer period of decay for the same reason as above.

3. The more mass at the headstock is another known contributing factor to create a longer decay.

4. The type of wood used in the guitar body construction is another factor. Hard woods will allow for a longer decay time than softer woods, e.g. Mahogany vs. basswood. This is because sound waves will travel faster as the density of wood increases which allows for better wave transmission. NOTE: most electric guitars may use many types of wood in their construction. Consider a Les Paul with a mahogany body, and a maple top, and an ebony fingerboard.

5. Heavier gauge strings will decay slower than light gauge strings as mass plays important role on wave transmission as well.

6. The nut and bridge material is also a factor. Again the density of the materials is significant. Consider the better wave transmission of graphite saddles vs. nickle.

Generally speaking a PRS guitar like the one Carlos Santana uses is optimized for his long 'sustained' notes, but that's only half the story, you should also see what pedals and tube amp he is using too.

Beyond the acoustic factors listed above, we should now examine the pick ups and the amplifier. There are a zillion pick ups out there, both single and dual coil (aka humbuckers) pickups will vary on how the sound is transmitted to the amp and this will have an apparent influence on the decay time. The settings on the amp and the amp build may have an influence as well. Foot pedals aimed at increasing gain and compression are factors too. Consider SRV playing a Strat through a tube screamer then into a vintage Fender Super Reverb with optimal NOS tubes, and a mix of AlNiCo and Ceramic speaker magnets.  Plenty of sustain.

Aside from using a "sustain effect processor" one could use any of the following to create sustain:

1. Ebow

2. Old school controlled amp sustained feedback (example Youtube video)

3. Use a real bow on a guitar with violin strings and an arched bridge.

4. Post production using a DAW. Record your piece, copy and splice the waves on and on together.

5. Loop the sound in an effects box.

Here's a website that discusses real vs fake sustain.

Here's an website that discusses real vs fake sustain: http://www.sustainiac.com/aboutsus.htm

Here's a website that discusses real vs fake sustain: http://www.sustainiac.com/aboutsus.htm