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A Fast Fourier Transform filter
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FogLAMP "FFT" C++ Filter plugin

A filter that applies a FFT algorithm to a set of readings.

Data is return in a single reading with a set of datapoints that each represent the average amplitude for a band of frequencies. These bands are created by dividing the frequency space into a number of equal ranges after first applying a low and high frequency filter to discard a percentage of the low and high frequency results.

E.g. if the lowPass filter is set to 15% and the highPass filter is set to 10%, with the number of bands set to 5, the lower 15% of results are discarded and the upper 10% are discarded. The remaining 75% of readings are then divided into 5 equal bands, each of which representing 15% of the original result space. The results within each of the 15% bands are then averaged to produce a result for the frequecy band.


The filter supports the following set of configuration options

The asset to apply the FFT filter to
The number of frequency bands to define the resultant FFT output into
The data that should be returned for each band. This may be one of average, sum, peak or rms. Selecting average will return the average amplitude within the band, sum returns the sum of all amplitudes within the frequency band, peak the greatest amplitude and rms the root mean square of the amplitudes within the band. Setting the output type to be spectrum will result in the full FFT spectrum data begn written. Spectrum data however can not be sent to all north destinations as it is not supported natively on all the systems FogLAMP can send data to.
The number of input samples to use. This must be a power of 2.
A percentage of low frequencies to discard, effectively reducing the range of frequencies to examine
A percentage of low frequencies to discard, effectively reducing the range of frequencies to examine


To build FogLAMP "FFT" C++ filter plugin:

$ mkdir build
$ cd build
$ cmake ..
$ make
  • By default the FogLAMP develop package header files and libraries are expected to be located in /usr/include/foglamp and /usr/lib/foglamp
  • If FOGLAMP_ROOT env var is set and no -D options are set, the header files and libraries paths are pulled from the ones under the FOGLAMP_ROOT directory. Please note that you must first run 'make' in the FOGLAMP_ROOT directory.

You may also pass one or more of the following options to cmake to override this default behaviour:

  • FOGLAMP_SRC sets the path of a FogLAMP source tree
  • FOGLAMP_INCLUDE sets the path to FogLAMP header files
  • FOGLAMP_LIB sets the path to FogLAMP libraries
  • FOGLAMP_INSTALL sets the installation path of Random plugin
  • The FOGLAMP_INCLUDE option should point to a location where all the FogLAMP header files have been installed in a single directory.
  • The FOGLAMP_LIB option should point to a location where all the FogLAMP libraries have been installed in a single directory.
  • 'make install' target is defined only when FOGLAMP_INSTALL is set


  • no options

    $ cmake ..

  • no options and FOGLAMP_ROOT set

    $ export FOGLAMP_ROOT=/some_foglamp_setup

    $ cmake ..


    $ cmake -DFOGLAMP_SRC=/home/source/develop/FogLAMP ..


    $ cmake -DFOGLAMP_INCLUDE=/dev-package/include ..


    $ cmake -DFOGLAMP_LIB=/home/dev/package/lib ..


    $ cmake -DFOGLAMP_INSTALL=/home/source/develop/FogLAMP ..

    $ cmake -DFOGLAMP_INSTALL=/usr/local/foglamp ..

Packaging for 'FFT' filter

This repo contains the scripts used to create a foglamp-filter-fft Debian package.

The make_deb script

Run the make_deb command after compiling the plugin:

$ ./make_deb help
make_deb {x86|arm} [help|clean|cleanall]
This script is used to create the Debian package of FoglAMP C++ 'fft' filter plugin
 help     - Display this help text
 x86      - Build an x86_64 package
 arm      - Build an armv7l package
 clean    - Remove all the old versions saved in format .XXXX
 cleanall - Remove all the versions, including the last one

Building a Package

Finally, run the make_deb command:

$ ./make_deb
The package root directory is   : /home/ubuntu/source/foglamp-filter-fft
The FogLAMP required version    : >=1.4
The package will be built in    : /home/ubuntu/source/foglamp-filter-fft/packages/build
The architecture is set as      : x86_64
The package name is             : foglamp-filter-fft-1.0.0-x86_64

Populating the package and updating version file...Done.
Building the new package...
dpkg-deb: building package 'foglamp-filter-fft' in 'foglamp-filter-fft-1.0.0-x86_64.deb'.
Building Complete.

Cleaning the Package Folder

Use the clean option to remove all the old packages and the files used to make the package.

Use the cleanall option to remove all the packages and the files used to make the package.

You can’t perform that action at this time.