This is a double bill walkthrough of Jorge Reales' Schroeder Reverb and his OPL synth. OPL is based on the Yamaha soundcard that was used in sound cards for PCs. It has all the features of OPL@ and some features of OPL3. A Schroeder Reverb is based on a series of all-pass filters and a parallel bank of feedback comb filters. The reverb is universal, the synth is iPad only.