deinvert is a voice inversion scrambler and descrambler. It supports simple inversion as well as split-band inversion.
By default, deinvert requires liquid-dsp, libsndfile, and GNU autotools. On Ubuntu, these can be installed like so:
sudo apt install libsndfile1-dev libliquid-dev automake sudo ldconfig
On macOS I recommend using homebrew:
xcode-select --install brew install libsndfile liquid-dsp automake
But deinvert can be compiled without liquid-dsp using the configure
--without-liquid; filtering will be disabled and the result will not
sound as good. It can also be compiled
without libsndfile using the configure option
support will be disabled, only raw input/output will work.
./autogen.sh ./configure [--without-liquid] [--without-sndfile] make
Note that since scrambling and descrambling are the same operation this tool also works as a scrambler.
If no input and output file is given, deinvert reads raw 16-bit PCM via stdin and outputs in the same format via stdout. The inversion carrier defaults to 2632 Hz.
Simple inversion, WAV input
(De)scrambling a WAV file with setting 4:
./src/deinvert -i input.wav -o output.wav -p 4
(De)scrambling split-band inversion with a bandwidth of 3500 Hz, split at 1200 Hz:
./src/deinvert -i input.wav -o output.wav -f 3500 -s 1200
Invert a live signal from RTL-SDR
Descrambling a live FM channel at 27 Megahertz from an RTL-SDR, setting 4:
rtl_fm -M fm -f 27.0M -s 12k -g 50 -l 70 | ./src/deinvert -r 12000 -p 4 |\ play -r 12k -c 1 -t .s16 -
Invert a live signal from Gqrx (requires netcat)
Set Gqrx to demodulate the audio (for example, narrow FM).
Go to the Audio window and click on the three dots button "...".
Go to Network and set host to localhost and port to e.g. 12345.
In the Audio window, enable UDP.
Run this command in a terminal window:
nc -u -l localhost 12345 | ./src/deinvert -r 48000 | play -r 48k -c 1 -t .s16 -
./src/deinvert [OPTIONS] -f, --frequency FREQ Frequency of the inversion carrier, in Hertz. -h, --help Display this usage help. -i, --input-file FILE Use an audio file as input. All formats supported by libsndfile should work. -o, --output-file FILE Write output to a WAV file instead of stdout. An existing file will be overwritten. -p, --preset NUM Scrambler frequency preset (1-8), referring to the set of common carrier frequencies used by e.g. the Selectone ST-20B scrambler. -q, --quality NUM Filter quality, from 0 (worst quality, low CPU usage) to 3 (best quality, higher CPU usage). The default is 2. -r, --samplerate RATE Sampling rate of raw input audio, in Hertz. -s, --split-frequency Split point for split-band inversion, in Hertz. -v, --version Display version string.
Inversion carrier presets
Can't find liquid-dsp on macOS
If you've installed liquid-dsp yet
configure can't find it, it's possible that
XCode command line tools aren't installed. Run this command to fix it:
Can't find liquid-dsp on Linux
Try running this in the terminal:
I hear a high-pitched beep in the result
This could be because the transmission has a CTCSS subtone.
It can be fixed by running a low-pass filter after deinvert. The cut-off
frequency should be around 250 Hz less than the inversion carrier frequency. For
example, if the inversion carrier is 3023 Hz, the
play command could be
play -r 12000 -c 1 -t .s16 - sinc -2800
deinvert is released under the MIT license, which means it is copyrighted to Oona Räisänen OH2EIQ yet you're free to use it provided that the copyright information is not removed. See LICENSE.