This week I started implementation of the ADSR envelope generator which will control amplitude/volume of each synthesizer voice. On the final design, when voices remain to be filled, each key-press on the input MIDI-controller will correspond to the triggering of its own envelope generator. At present, the generator takes in attack, decay, sustain, and release parameters along with a key-press parameter. It generates a waveform which will be used to scale oscillator amplitude.
What I’ve written so far will detect key-press and release events, and transition through the different phases of the envelope. The envelope output-level is updated with an increment each clock-edge so that the slope of each stage in terms of level-change/unit-time can be tuned to user-levels without using floating-point operations.
The timing is still under-development, at present, the envelope updates each clock cycle, instead of having a separated control-timing signal. So for the coming week as I continue this design, I’ll separate this piece out so that the parameter tuning corresponds to the scale of audible-noise, and not the internal clock. After this is done, the envelope should be connected to the output of our wave-adder Shayaan was working on this week to see if we can then modulate amplitude upon a key-press.
I’ve opened a pull-request for what I’ve committed this week visible here: github link.
This week, we also finalized our design report.
In consideration of global factors, this synthesizer is designed as a standalone hardware instrument, as opposed to the most readily-available alternatives right now: software synthesizers requiring a PC. Our FPGA design can be operated without requiring access to a personal computer. Further, if the design were later implemented on a dedicated PCB, we could extend the availability as a low-cost device. Taking this approach would improve access for any musician or hobbyist without the means to invest in more powerful synthesizers.