|We've got signal, but what the heck is it?
That's your mission. Analyze this bébé.
download the audio file 17.wav.bz2
No need to bunzip2 this file since baudline can automatically uncompress
Setup baudline to be a Web Browser helper application as described in the
Slow down the play back speed to 0.125X or 0.250X with the
Play Deck's speed control
and listen for sonic details that would otherwise be missed.
Use a larger FFT size, a narrow
Gaussian window, and the
harmonic bars to determine
the low frequency harmonic relationships.
Use the periodicity bars
to measure the timing between the wideband events.
The high frequency bandwidth looks like it would extend past 24kHz if a higher
Nyquist sampling rate was used.
What does the purple and green banding signify?
What do the decay tails at 7500 and 12500 Hz signify?
What is it?
This mystery signal is the mechanical double click sound of a 3-button
Logitech optical wheel mouse
. The file has two distinct double click events while only one event
is visible in the above spectrogram.
Two microphones, one on each of the left and right sides of the mouse, recorded
the clicks in a close stereo layout. The purple and green banding at
first looks like a natural phasing effect but further observation shows that
the even and odd impulses share a unique signature.
A Gaussian window with a beta of 5.0 was used to improve the time resolution
of the spectrogram image. This allowed the observation of two useful
features; periodicity and ringing.
The 4 impulses appear to be evenly spaced quadruplets but careful use of
baudline's periodicity bars shows that there is a large amount of variation
between all the impulse. The delta spacing ranges from 75 to 98 ms.
The tightening of the broadband impulse also allowed the ringing decay tails to
be visible. The decay tails at 7500 Hz only occurs with the first and
third impulses while the 12500 Hz tails occur with all 4 impulses. This
even-odd ringing behavior matches the color banding mentioned above.
What is happening is that the button down press allows part of the metal switch
structure to ring at 7500 Hz while the button up release action mechanically
damps the ringing.
The harmonic helper bars show that the ringing at 450, 630, 2100, 7500, and
12500 Hz is not harmonically related. The frequency structure of ringing
bells is similar so this isn't that surprising.