Phone Tap Audio Enhancement

Question

Hello
I suspect that my phone is tapped using the pizeoelectric buzzer.
More on how this is done is discussed here:
https://www.schneier.com/blog/archives/2010/01/eavesdropping_i.html
There's so much noise on this audio that I can't filter it out. A series of filtering and then amplifying and I can vaguely hear the audio.
The tapped phone audio is here:
https://docs.google.com/uc?export=download&id=0B5ingIYMt2rmZVRJSUQwZi1wRWc
And the target audio is here:
https://docs.google.com/uc?export=download&id=0B5ingIYMt2rmVy16emVzdXRNcHc
The first ten seconds of the phone audio, I tried to keep the room silent. At ten seconds I began playing the target audio.
Can anyone help me extract the target audio from the phone tap recording?
Many thanks!

Answer 1

Hello Steve
Thank you for taking a look.
I think I may have mixed up the files or something.
I'll upload another file in four hours when I get home.
I'm convinced my telephone is compromised and leaks audio down the line.
This method is well known by the intelligence community.
I'm not an audio expert but can software like Audacity and Audition do the work of High-Gain Audio Amplifier?
The Marty Kaiser amplifier was used to amplify and filter out noise from telephones where the ringer was used as a microphone.
Read the comment by Kevin D. Murray at
https://www.schneier.com/blog/archives/2010/01/eavesdropping_i.html
I quote:
"Hook a high-gain audio amplifier.....You'll believe."
There's another interesting discussion here:
http://yarchive.net/phone/infinity_transmitter.html
I quote:
There is actually another methodology which can be applied to
eavesdropping on room conversations using an unmodified telephone set.
Most ringers will function as a variable reluctance microphone, if the
line from the telephone is amplified to an extreme degree, along with
application of suitable signal processing to eliminate an incredible
amount of noise. As in the above methods, the necessary apparatus
must be within a few hundred feet from the telephone set, and the CO
pair must be broken during the operation (with circuitry to detect an
incoming call or outgoing call attempt and reestablish the CO line
continuity to avoid any suspicion on the part of the subject). I am
not claiming that a ringer is a *good* microphone, but under some
selected circumstances this technique can provide useful intelligence.
I may later regret this suggestion, but as an example to
illustrate this principle, here is an experiment that an enterprising
reader can perform using apparatus found in any well-equipped
electronics laboratory. Take a 500-type or 2500-type set with a
bridged ringer and connect its tip and ring directly to the input of a
low-noise amplifier providing say, 80 dB of gain in the voice
frequency range. A suggested approach is to cascade two
Hewlett-Packard 465A amplifiers, with each amplifier being set for 40
dB gain. Take the 80 dB amplifier output and connect it to the input
of a variable bandpass filter having at least 20 db/octave attenuation
(like a Kron-Hite 3100, 3500 or 3700). Take the output from the
bandpass filter and feed it to another amplifier providing 20 to 40 dB
gain and capable of driving a pair of headphones.
Tune the bandpass filter to reject powerline noise, and you have just
turned the telephone set into a crude microphone. At that point it
does not take much imagination to realize that given some competent
engineering resources and a commensurate budget, this technique can be
refined into a practicable eavesdropping device. The availability of
digital signal processing can also do wonders to eliminate the vast
amount of power line, impulse noise and other interference which
develops at the gain necessary for speech pickup sensitivity.
While electromechanical ringers are becoming somewhat a thing
of the past, many electronic telephone sets with tone ringers will
function as an even better microphone. Such tone ringers usually rely
upon a piezoelectric element as the loudspeaker, although a few
low-quality "drugstore-variety" one-piece telephones utilize the
receiver element as the ringer transducer. As most readers of this
forum are no doubt aware, piezoelectric devices will generally
function as both a microphone and loudspeaker. Even a piezoelectric
element optimized for tone ringer use, i.e., with resonance in the
range of 1.5 to 2.5 kHz, will still function as a usable microphone
for lower frequencies.
An on-hook telephone set with electronic tone ringer, if
isolated from the CO line and connected to an ultra-high gain
amplifier with suitable bandpass filtering, and if also subjected to
an appropriate RF bias to cause conduction across the initial
full-wave bridge rectifier and subsequent semiconductor junctions, can
in many instances be turned into a microphone. While this technique
will not work with all electronic telephones, it will work with a
significant number.
The above technique of compromising a telephone with an
electronic tone ringer was first performed almost twenty years ago on
the Ericophone. The Ericophone was an early one-piece telephone, some
models of which contained an electronic tone ringer. While the
geometry of the Ericophone defies verbal description in this forum,
the overall design scheme may best be described as phallic in nature.
Those readers who are familiar with the Ericophone will no doubt
concur with this description :-)."