I just have my laptop now, so I’ll prove this is possible with the LOWEST quality samples.
Step one (pic) (audio): my finger snapping (recorded on MacBook mic)
Step two (pic) (audio): playing a scale on this snap using Simpler
Step three (pic) (audio): looping the sample and shortening the loop, effectively turning the sample into a “grain.” Notice the timescale in the picture.
Step four (pic) (pic) (audio): turning on the lowpass filter and adjusting release to make the granular synth sound more ‘piano-like’
If you use a different sample, your final instrument will still be usable but will have slightly different tonal qualities as you turn it into a grain. I find that complex tones such as a cough have quirky tonal properties (Harpsicough.mp3) in this study, while simpler sounds like my snap tend to sound more pure and piano-like when they’re done becoming grains.