This project focuses on the development of a Raspberry Pi based musical synthesizer with a variety of user inputs. The MIDI controller used in this case is an AKAI LPK25 Laptop Performance Keyboard.
The following diagram illustrates the setup of each component:
The synthesizer works by utilizing a variety of python packages/distributions and MIDI software. The MIDI software utilized for real-time playing is Fluidsynth, and is based on the Soundfont 2 specification. Fluidsynth generates audio by reading and handling MIDI events from MIDI input devices, such as our keyboard, and by using a desired SoundFont in the form of an sf2 file. Because the keypad is an I2C device, the python script utilizes CircuitPython which is a microcontroller software, alongside a python distribution that utilizes the CircuitPython library for this specific piece of hardware.
The synthesizer works by plugging in a MIDI controller into the USB port of the Raspberry Pi. Upon turning on the Raspberry Pi and logging in, the python script runs in the background.
This script listens for the black button to be pressed, and in doing so, starts up the Fluidsynth as a server, uses the ALSA sound module, and connects the MIDI controller client to the Fluidsynth client. From there, the blue and green buttons, as well as the keypad, may be used. Because Fluidsynth takes commands from its own proprietary shell, the Telnet python module is used to send commands to the Fluidsynth server.
The blue button is used to send a command to Fluidsynth to turn on the chorus effect, and after another push, turns it off.
The green button is used to send a command to Fluidsynth to turn on the reverb effect, and after another push, turns it off.
The keypad is used to change the instrument being used, with each key sending a command to Fluidsynth to select a specific instrument.
The asterisk and pound keys send a command to Fluidsynth to change the value of the gain. Upon each push of the asterisk/pound key, we decrement/increment the value of the gain by 0.5, then send that value to Fluidsynth.
The user may play as much as they like, and when finished, may press the black button again, which kills the Fluidsynth program currently running. Because the python script runs in the background, and constantly awaits the press of the black button, the user may turn this off and on at their own leisure.