This is probably the best SPC player of them all. It has a myriad of features: speed/pitch change, channel mute, echo disable, DSP pitch/volume registers, etc.
Use the left and right arrow keys to toggle the data viewed during SPC playback.
v2.17.7 (build 5616) (2016/08/27)
This updated version of spcplay fixes the pitch modulation amplitude (for example, FF6 Kefka's laugh).
The version currently on here may not work with songs that deliberately try to overflow the FIR coefficients... such as a couple of my own pieces of music, actually, the second one made with none other than my own fork of AddMusicK, AddMusicKFF. And I don't even crash the sound driver (or audio) in the process of doing so!
I reported this on Github and there's a prerelease version that fixes the bug, albeit I retroactively realized that there was a safety feature in there that prevents volume levels from going out of control.