Month: December 2014

Processing shortwave radio sounds

Using the python sms-tools library.

sms-tools: https://github.com/MTG/sms-tools

Here is a song made from the processed sounds:

mp3 version:

This project was an assignment for the Coursera “Audio Signal Processing for Music Applications” course. https://www.coursera.org/course/audio

Source material

Sounds were recorded from a shortwave radio between 5-10MHz.

freesound.org links to the sounds:

 

Processing

am_interference_7mhz.wav

The sound is an AM shortwave broadcast station from between 7-8 MHz. It is speech with atmospheric noise and a digitally modulated carrier at 440Hz in the background.

I tried various approaches to removing the speech and isolating the carrier. But ended up using the following parameters to remove noise and speech, but for most part leaving a 440hz digital mode signal with large gaps in it.

  • M=701
  • N=1024
  • minf0=400
  • maxf0=500
  • thresh=-90
  • max harmonics=50

After more experimentation, the following changes resulted in a cool continuous tone with speechlike quality (but not intelligible) and the background noise is gone.

Here is the full list of parameters:

am_interferece_7_mhz_harmonic_model_2_params

Here is a plot:

Screen Shot 2014-12-16 at 8.03.55 PM

Here is the resulting sound of the sinusoidal part of the harmonic model:

buzz_pulse_7mhz.wav

The sound is continuous digital modulation (buzzing) from a shortwave radio between 7-8 MHz. The buzz is around 100Hz with atmospheric background noise.

Transformation using HPS (harmonic plus stochastic) model.

Not very impressive analysis, but the resynthesis had a very cool looking spectrogram due to some frequency shifting.

buzz_pulse_hps_params

Screen Shot 2014-12-16 at 8.12.43 PM

I realized that I had set f0min too high. Went back to using the HPR model without transformation to see if I could separate the tone. Here is the plot:

buzz_pulse_hpr_params

Screen Shot 2014-12-16 at 8.33.50 PM

Here are the resulting sounds transformation (unused) and the sinusoidal/residual results that were used in the track.

source: digital_pulse_7hz.wav

A repeating pulse around from a shortwave radio between 7-8 MHz. The frequency of the pulse is around 1000Hz with a noise component.

Another noise filter – this was way more difficult due to high freq material.

digital_pulse_hpr_params

Screen Shot 2014-12-16 at 8.40.12 PM

Instead, I went with a downward pitch transform, using the HPS model transform. Here are the resulting sounds from  the HPR filter (unused) and the HPS transform.

cw_7mhz1_small.wav

The sound contains typical amateur radio CW signals from the 40 Meter band, with several interfering signals (QRM) and atmospheric noise (QRN). Using the HPR model, I was able to completely isolate and re-synthesize the CW signal, removing all the noise and interfering signals.

cw-params

Note that you can actually see the morse code letters “T, U, and W” on the spectrogram of model!

Screen Shot 2014-12-16 at 8.55.20 PM

Here is the re-synthesized CW sound:

wwv_5mhz_short.wav

The WWV National Bureau of Standards “clock” station at 5MHz. A combination of pulses, tones, speech, and background noise.

I was trying to separate the voice from the rest of the tones and noise. After several hours and various approaches, I gave up. The signal may be too complex to separate using these models. There were some interesting plots with the HPR model

Screen Shot 2014-12-16 at 9.11.54 PM

Finally decided to just isolate the 440 Hz. clock pulse from the rest of the signal:

wwv-tone-extract-params

Screen Shot 2014-12-16 at 9.06.09 PM

Here is the resulting sound (note that the tone starts several seconds into the sample)

ep-413 DSP week 15

Review

  1. Syllabus: http://reactivemusic.net/?p=17122
  2. Ways to approach a project http://reactivemusic.net/?p=17132
    • Make machines that make art
    • Reverse engineering
    • Use the wrong tools
    • Abstraction and destruction
    • Backwards, extreme, opposite – connect two things
    • Ask questions
  3. Composition tools and dramatic shape http://reactivemusic.net/?p=17157
  4. Problem solving (pitch detection) and prototyping (Muse) http://reactivemusic.net/?p=17159
  5. Sound byte composition http://reactivemusic.net/?p=17190
  6. Convolution and voices http://reactivemusic.net/?p=17211
  7. (No class this week)
  8. Granular synthesis, the frequency domain, and phasors http://reactivemusic.net/?p=17360
  9. Data, Internet API’s, Vine API in Max http://reactivemusic.net/?p=17466
  10. Communication, Osc, Sonification, MBTA API in Max http://reactivemusic.net/?p=17518
  11. Filters: analog, digital, other, reversability http://reactivemusic.net/?p=17542
  12. Web Audio API http://reactivemusic.net/?p=17600
  13. Feature detection, and Music Information Retrieval http://reactivemusic.net/?p=17689
  14. Waves: light, radio, water http://reactivemusic.net/?p=17787
  15. This
Ideas

John Coltrane: You can learn something from everybody, no matter how good or bad they play, everybody has something to say.

Sal Khan: In the future people will take agency for their own education.

For artists, everything is a tool.