Here is a tool I built a tool to help me figure out what pokey sounds on the 7800. It lets me test out sound mixing on all four channels at the same time.

You can view it here;  JS7800: Atari 7800 Emulator (raz0red.github.io)

Controls:
-Joystick/arrow keys select the value to change (orange)
-Left button (z) increases value, right button (x) decreases value (z= button 1, x=button 2)

– F = Frequency

-W =Waveform

-V = Volume (needs to be > 0 to hear anything)

-D = Duration (how many frames to play the sound)

-S = Silence  (amount of time between plays to keep channel silent)

-T = Type  (C)onstant (play at same volume), (A)attack (play from volume 0 to 15, (D)ecay (play from volume 15 to 0) 

This is the first version. Suggestions much appreciated.  

link: JS7800: Atari 7800 Emulator (raz0red.github.io)