This week, I worked on developing the RTL for the ADSR and the wavetable sampling. I also worked on the design report, and thought through the implementation details for various subsystems in the RTL that I was working on. This involved the design of the ADSR RTL and FSM. Although it was simple, the design helped guide my implementation process. I’ve attached a diagram of the FSM below, which I used when implementing my design.
These attack, decay, sustain, and release times will eventually be set by the user, and configured in order to provide a dynamic filter and amplitude response. Additionally, I worked on understanding BLEP (Band-Limited Step Functions) to correctly interpolate sounds when working with signals like square, saw, and triangle. The use of BLEP allows the sound to avoid infinite harmonics and harsh frequencies, creating a continuous change rather than a sudden discontinuous jump. Through this, we are able to preserve the harmonics of the sound while avoiding harsh frequencies, at the cost of minimal additional memory usage and simple digital logic.