I'm using Sonar 8, Windows Vista, Edirol UA-4FX box, either a Rohde condenser mike or an SM58. Trying to record acoustic guitar and in certain places I want a slow strum or reverse arpeggio to just sustain and ring as long as the guitar can keep it going, which with my guitar is at least 10-15 seconds. But when I record this section and play it back, the sound tapers off long before the guitar is finished resonating. I spoke to a pro audio engineer friend about this and he said it sounded like a gating issue somewhere. If so, where in my system should I look? I've tried using the Sonitus Fx gate effect and can only get a modest improvement in the decay time. And shouldn't there be a default someplace in Sonar where I can set the gating to allow for a long decay? If so, where is it? It seems pretty weird to have to adjust this sort of signal after recording when an old analog system would have just let the thing ring in its original form. Help!! Thanks! veebeejeebee

I don't even have to look up your interface to guess that by it's name it has built in efx, I also will guess it has a GUI mixer interface where you can set thing like gates and EFXs which will be added before the signal is sent via the USB to the computer. Look there. 

"I want a slow strum or reverse arpeggio to just sustain and ring as long as the guitar can keep it going.."
Maybe I'm missing something here. A gate or its low ratio ver 'expander, does just the opposite- attenuates the signal faster as it decreases.
Or are you suspecting there was a gate on it and you're trying to find and disable it..?
 
Also once you get that sorted out, I'd be looking at clip' and/or track volume envelopes to raise the levels as needed- That way you can tailor the gain, rise and fall shapes, length all custom fit.
Someone will advise 'compression as well and that's a different and valid sound. But (likely) you may still need a lift' on the tails.
 
(There we go. Guess i forgot 'firefox don't work to good here?

it may be less a gate issue as more a sustain issue.but i would remove all plugins and see if it still happens,if it does,cactus may be right,your interface might be adding compression or gate somewhere in the mix.

what is this interface ?

Yep, I agree with Charlie.

Strip ALL processing away, including EQ. Just listen to the raw sound of what you recorded.

Does it sound like your guitar in the room?

If not then maybe you need to experiment with different mics & their placing.

You need to get as close to what you're hearing in the room before applying any processing.

You can hit the [F/X] button on the Control bar to check Charlies theory out.

Does the wave form on the track indicate any sign that the sustain is still there? or does it drop off/flatline about where your wanting it to still continue?