Music Synthesis in Hardware

Howard Mao

April 25, 2013

ROMboard: An FPGA-based Musical Instrument

http://www.youtube.com/watch?v=ap7QOzf1rpI

What’s an FPGA?

I A prototyping platform for digital hardwareI Write a description of a circuit in a hardware description

language (HDL)I FPGA contains a bunch of configurable logic blocks (CLB)I Design tools take HDL code and compiles it to CLB settings

for FPGA

How do we make Romboard?

Part 1 - Audio CODEC

I CODEC stands for COder DECoderI Turns digital signals into audio signals

Part 2 - Clock DividerI We want to generate a square wave as the audio signalI Why square wave? It’s easier to do in hardwareI Problem: how do we get the right frequency?I Hardware clock is at 50 MHzI Our music range is 130 Hz (1 octave below middle C) to 523

Hz (2 octaves above middle C).I Answer: count up to 50MHz

2f then flip the output

Part 3 - Input Handling

I How do we choose notes based on input?I 4 Pushbuttons, 17 switchesI Pushbuttons give 1 when up, 0 when downI Switches are 0 when off, 1 when onI Use switches to select what notes the pushbuttons map toI Pushbuttons + Switches -> Max count for clock dividerI Use a ROM (Read-Only Memory) to store these values (That’s

why it’s called ROMboard)

Part 4 - Putting it all together