What is baudline?
Mystery Signal
Mystery Signal of the Month   Jan 20 2005
We've got signal, but what the heck is it?
That's your mission.  Analyze this bébé.

mystery spectrogram                                                                                                                                                          

download the audio file 13.wav.gz

hints :

  • No need to gunzip this file since baudline can automatically uncompress files.
  • Setup baudline to be a Web Browser helper application as described in the FAQ.
  • Try playing the mystery signal at a slower quarter (0.25X) or half (0.5X) speed.
  • Use the Color Aperture window to focus and maximize the color resolution to the -10 dB to -60 dB range.  Changing the RGB curve shapes in the Color Picker window might also be helpful.
  • Explore the signal with the Histogram and Waveform windows at different zoom levels.  Are there any interesting and unique characteristics?
  • This is a 3 channel .wav audio file.  To listen to the 3rd channel or if you have multiple sound cards and are experiencing play back problems then open up the Output Devices window and adjust the channel enabling / mapping controls.

What is it?

It is the baudline visualization tool looking at itself.  The above image is a baudline spectrogram of the baudline x86 executable code.  The Raw Parameters window was used to open the baudline x86 binary as a strided 3 channel signal file.  Equivalently this can also be accomplished using baudline's standard input option with the following command:

  • cat baudline | baudline -stdin -channels 3

code and data
This mystery signal looks and sounds a lot like a negotiating modem with the familiar tone and noise bursts.  The tones are periodicities in the x86 binary created by repeated code blocks or internal data tables (see the waveform above).  The noise bursts are sections of executable x86 code that are fairly random in byte structure and haven't been unrolled.  So the baudline code and data segments are responsible for this interesting and strange looking spectrogram.

There are a number of insightful periodicities in this mystery signal and they can be measured with baudline's Periodicity measurement window.  Setting the fundamental rule option to "mouse exact" or "mouse climb" with allow the periodicity value to track the mouse cursor position.  The periodicities of 4, 8, 31.0303, 89, and 137 can be all be seen.

stride by 3
A channel stride of 3 does a number of interesting things:
  1. From a DSP perspective it is like decimating without filtering which causes aliasing.
  2. It scrambles / chops up the data by a factor 3 which is the first prime number that is not a power of 2.  This can reveal new relationships that should not be inherent in the data.
  3. It generates 3 channels for a colorful RGB overlay display where spectral color denotes base 3 origin.
For comparison see the stride by 1 spectrogram image below.  It looks very similar to the initial stride by 3 image.  Many features are the same and some have changed slightly.

Experimenting further with the Raw Parameter's Decode Format option will result in many new relationships with some of them being quite unexpected.  The 1 bit binary (msb and lsb), 8 bit linear (signed and unsigned), and 16 bit linear (big endian) are decode options all worth exploring.

Copyright © 2005 SigBlips.com - group - blog - site map