In video 51, I am using a flexible envelope -- not an envelope follower. The flexible envelope can be mapped to the frequency of the 32-step modulator (for example). Now, the speed of the step modulator will go up and down according to the shape of the envelope. For example, if you draw a shape like a mountain. The step modulator will speed up until it hits the "peak" of the mountain, and then it will slow back down as it heads to the valley. You need to play with the modulation intensity for the envelope as well as the default frequency setting of the step modulator. An envelope follower works differently. It is useful if you want the behavior of one sound to follow the behavior of another. For example, if you have a piano patch that you play loud and hold, the attack is quick and the decay is long. If you set up an envelope follower that controls a filter, the filter will open quickly with the piano's attack and then close slowly as the piano decays. Play around with it, and let me know how it goes. And thanks for the kind words about the tutorial!