https://github.com/pdmccormick/de2-polyphonic-audio

Polyphonic tone generation demo for the Altera DE2 FPGA dev board with NIOS II soft core processor.
https://github.com/pdmccormick/de2-polyphonic-audio

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Polyphonic tone generation demo for the Altera DE2 FPGA dev board with NIOS II soft core processor.

• Host: GitHub
• URL: https://github.com/pdmccormick/de2-polyphonic-audio
• Owner: pdmccormick
• Created: 2013-11-09T17:26:53.000Z (about 11 years ago)
• Default Branch: master
• Last Pushed: 2013-11-09T17:37:31.000Z (about 11 years ago)
• Last Synced: 2024-04-21T09:30:54.565Z (7 months ago)
• Language: C
• Homepage:
• Size: 219 KB
• Stars: 1
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.txt

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README

        
DE2 Polyphonic Audio Demo

=========================

Peter McCormick

[email protected]

Introduction

------------

This is a small demo of driving the audio outputs on a DE2 FPGA dev board

running a NIOS II soft core processor, by polyphonically mixing pitches from

over two octaves of a C major scale (with the notes controlled by the slider

switches.)

This code is placed in the public domain, provide 'as is' and without any

warranty whatsoever. The user assumes all risk by running or using it.

Getting Started

---------------

Using the Altera Monitor Program, create a new C language project and add all

the C (*.c) and assembly code (*.s). Under 'Memory Settings', set the "Start

offset in device (hex)" fields to '1000' for both the .text and .data section

(this offset makes room for the exception handler code.) Download to your DE2

board, plug in speakers or headphones, compile and run.

Use the slider switches from right (SW0 as C4) to left (SW17 as F6) to play

scales, chords or melodies.

WARNING: Beware that the audio played is at full volume (amplitude), so either

use speakers with a volume control or do not immediately put your headphones up

to your ears until you know just how loud that is.

Ideas

-----

Change mono output to something interesting in stereo.

Save 48KB of memory by noticing that the second half of the `sine_wave` array

is a reflected, negated version of the first.

Implement a multi-thousand sample software FIFO that feeds into the hardware

FIFO to ease timing restrictions.

Handle audio input and output together (whether in pass-through or simply up to

a higher layer of software.)

Generate harmonically richer tones than pure sine waves.

Implement a mixing strategy more sophisticated than just averaging.

Add effects like chorusing or delay.