Some technical details then, if you’re interested!

www.nesdev.org/wiki/APU#DMC_($4010–$4013)

The most important point for getting “higher” quality audio from it is probably this:

The $4011 register can be used to play PCM samples directly by setting the counter value at a high frequency. Because this requires intensive use of the CPU, when used in games all other gameplay is usually halted to facilitate this.

Which is why you generally only heard it on title screens. Usage in games was much rarer, and usually much shorter samples.