Question: I have an instrumental here (not particularly a fan of, but great reference for this question.)

This instrumental starts off with and contains a synth pluck with a simple melody. My interest in this synth pluck is how a single sound can fill out the sound spectrum all by itself. 

What is the process behind achieving this in mixing? I suspect its a reverb with a long decay but i could be completely wrong.

How is it done?

Thank you!

Answer: 
From my answer to [your stereo reverb question](https://music.stackexchange.com/questions/92393/what-is-the-difference-in-using-mono-reverb-vs-stereo-reverb)

> 
> It's worth noting that (mono-in stereo-out) stereo reverb is one way
>  to artificially create a stereo field from a mono input. Other
>  stereoization methods include comb filtering with a delay on one of
>  the stereo channels, complementary comb-shaped EQ curves for
>  left/right, and special stereo chorus effects.
> 
> 
> 

Here's an example of how to widen a sound with Ableton's stock chorus and reverb:
From the comments you seem to be asking not about the frequency spectrum, but about the stereo field.

Yes, this is probably done by adding pseudo-stereo information using a 'stereo reverb' plugin.

It conceivably COULD have been achieved by recording the (marimba?) sound in a very reverberant room with stereo microphones, but I suspect it's a dry sample with artificial reverb applied.