Vibrato(FM) effect on DE2

the example from the link is very simple, it doesn't require reading from RAM twice for every sample

you will take the variable-length delay you've already written. register the output of the delay (register again if you are already registering it once). then sum the output of the delay and the registered output

in a first test you could leave out the (n) and (1-n) multipliers and just let the signal grow, and send the most significant portion of the output word to the DAC. next you could add the multipliers in and experiment with fixed values or maybe even some kind of real-time control. MIDI is pretty easy to add