ep-4yy13 DSP – week 13

“I think its just the biggest conceptual art project uninentional or otherwise that anyone ever made. it puts Christo and those other guys to shame. Its planetary”

Roman Mars “Episode 97 – Numbers Stations” from 99% Invisible


  • Measuring the invisible
  • What is the difference between sound waves and radio waves?
  • What is an antenna?
  • Wave propagation is frequency dependent
  • Sunspots and magnetic fields http://spaceweather.com
  • Extreme frequencies, negative frequencies?


Internet radio streams and recordings

Frequencies and modes
  • Macbook trackpad: Noise 5 mHz. (try holding radio near screen too)
  • Macbook AC adapter: Noise 600-1400 kHz. (~1000)
  • AC adapters, LED’s, Utility poles: 3.2 Khz
  • Arduino transmitter: AM 1330 kHz.
  • Laser light at 650nM
  • Wireless micorophone (Orange-brown): Wide FM 614.150 MHz. (R band)
  • Cordless phone: Narrow FM 926 mHz.
  • Cell phone: Digitally encrypted trunking FM 836 mHz.
  • Wifi: Digitally encoded PCM 2.4 gHz.
  • FM broadcast band: Wide FM 89.7 mHz (Raspberry Pi example 98.1 Mhz)
  • TV audio 600 mhz/660 mhz FMW
  • The sun http://www.ips.gov.au/Solar/3/4

Topics not covered

(due to snow and stuff)



  • d3
  • processing
  • jitter
  • hardware control




Please send me a copies of your earlier compositions. Have a prototype ready to demonstrate or talk about for the next class.


notes for Berklee EPD presentation 4/30/2014

Web Audio API

other projects:

tz – examples

Internet sensors project updates


pifm r-pi transmitter


How to stop pifm from broadcasting:


An alternative r-pi transmitter using Sony Ericsson mmr-70 https://github.com/Manawyrm/FMBerry

A playlist script http://bytesare.us/cms/index.php/geeky-toys/pi-as-fm-radio-mp3-transmitter

bandpass filter http://www.radio-electronics.com/info/rf-technology-design/rf-filters/simple-lc-bandpass-filter-design.php

pigpio library (to edit gpio pins) http://abyz.co.uk/rpi/pigpio/

WSPR transmitter using r-pi https://github.com/threeme3/WsprryPi (also a project here called piBits that does fm transmitter)

cw  beacon xmtr http://hackaday.com/2013/01/25/raspberry-pi-used-as-a-beacon-transmitter/

sub transmitter (claimed): http://www.southgatearc.org/news/may2013/ssb_using_a_raspberry_pi.htm#.U1iZ1F4ifnk and here: http://wsprnet.org/drupal/blog/1522