A simple implementation of a DSS-based musical synthesizer with minimal cost (less than $10) hardware.
The application was designed for the PSoC® 4 CY8CKIT-049 42xx cheap evaluation kit, which uses a 48MHz ARM Cortex-M0 microprocessor. Code includes cypress-specific interrupt and peripheral handling. However, it should be adaptable to all 32-bit ARM microcontrollers.
Application requires a filtered DAC with at least 8-bit depth. Implementation uses embedded IDAC with a ~1K resistor to the ground, followed by a simple lowpass-filter (~80Ohm resistor + 0.1uF capacitor), and finally the internal OpAmp as Unity Buffer. Output should be connected to a speaker or audio jack.
- Sine wave generation with DSS
- Voice polyphony - tested for up to 16
- MIDI over UART
- Smooth output clipping to [-1, 1] range
- Alias-free waveforms on any frequency via interpolation
- ADSR envelope for notes
- More waveforms
- MIDI channel handling
- MIDI CC handling for parameter modification
- Tweakable low/high-pass filter
- Unison mode
- Pitch bending
- Tremolo & vibrato
- LFO
The aplication uses an interrupt routine called every 480 clock cycles, effectively calculating samples by one and pushing them to the DAC with 50khz rate, skipping any buffering.
Synthesizer uses soft clipping using the 1.5x-0.5x^3 polynomial function after the final mixing.
Upon receiving a note-on event, voice pool selects a etiher a most recently released voice, or the oldest active one.