The Instrument Block

Different to note blocks, this block can be crafted using a noteblock, a goat horn, and amethyst.
While note blocks activate once and play a single sound, instrument blocks keep playing (holding) an instrument while it is activated.

Technically this can be achieved by providing 3 samples to the instrument block: a start sample, a looping sample, and a release sample. When the note is first activated the start sample plays, followed by the looping sample as long as the block stays on. Finally, the release sample is played when the instrument block is depowered.
Multiple sets of samples can be assigned to the same instruments for different pitch ranges (similar to how modern samplers work)

Left clicking the instrument block will play the samples as if they were powered for half a second.
Right clicking the instrument block will set the note, playing the samples for a similar amount of time

The signal strength that is provided to the instrument block will determine the volume of the instrument block.
The block placed below the instrument block selects the instrument (similar to note blocks, excluding percussion
Placing a solid block above it will mute it
Optionally, placing certain transparent blocks can trigger certain modifications or filters to the instrument:
Glass: Low-pass filter
Cobweb: High-pass filter
String: Vibrato (ooOOooOOoo)
Bell: Long release (the piano pedal effect ig)

This provides an extended ability for minecraft musicians to thrive!