This project focuses on the development of a digital guitar effects pedal using a micro-controller. I explored digital signal processing techniques to apply a variety of effects to an electric guitar’s audio signal in real-time.

The hardware, a STM32F7-46NG board with a WM8994 audio codec, provides a robust foundation for this work.

Features

• Real-time processing with low latency.
• Touch-based GUI with precise parameter display.
• Effects: Delay, Flanger, Vibrato, Tremolo, WahWah, Distortion.
• Multiple concurrent effects.
• Simple, reprogrammable system architecture.

The hardware core is the STM32F746NG board with an ARM Cortex-M7 processor for DSP. The integrated WM8994 handles A/D and D/A conversion.

Firmware was developed in C for real-time efficiency. DMA automates audio data transfer, ensuring a continuous stream. The UI prioritises a simple, functional design with low processing overhead.

I2C is the communication protocol used to talk to the WM8994 audio codec. The Effect struct contains all data for a single effect, including its name, an array of its Parameters, and a pointer to the audio processing function.

The firmware’s core logic is managed by two DMA callbacks: BSP_AUDIO_IN_HalfTransfer_CallBack() and BSP_AUDIO_IN_TransferComplete_CallBack()

This double buffering ensures that while the audio codec is playing one buffer, another is filled with processed audio, preventing audible delays.

All audio data is handled as a 16-bit signed integer (int16_t) format, which allows for processing on a range from -32,768 to 32,767.