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FreqTweak is a tool for FFT-based realtime audio spectral manipulation and display. It provides several algorithms for processing audio data in the frequency domain and a highly interactive GUI to manipulate the associated filters for each. It also provides high-resolution spectral displays in the form of scrolling-raster spectrograms and energy vs frequency plots displaying both pre- and post-processed spectra.

It is an extremely addictive audio toy, but I hope it has value for serious audio work too (sound design, etc). The spectrum analysis is pretty useful in its own right.

Version 0.6.1 released -- 7 July 2004 -- various fixes to satisfy compilers -- modulator preset loading fixes -- jack tmpdir option fix
Version 0.6.0 released -- 23 April 2004 -- added filter Modulators, Rotate, Rotate LFO, Value LFO, and Randomize -- minor bugfixes
Version 0.5.3 released -- 18 Sep 2003 -- reworked all string handling to be compatible with unicode versions of wxGTK -- 64bit portability fixes -- added usage help
Version 0.5.2 released -- 20 Aug 2003 -- fixed dialog closing problem, made them real windows -- fixed compile problems for gcc 2.96 -- added Compressor module -- added EQ Boost module -- now supports FFTW3 -- manpage contributed by Enrique Arnuncio
Version 0.5.1 released -- preset loading bug fixed
Version 0.5.0 released -- -- arbitrarily selectable and reorderable modules -- preset blending feature -- two new modules: limiter and warp -- new preset format (conversion script available) -- internal design cleanup

The preset format has changed for 0.5.0 and above. Use the included ft_preset_convert.py script to convert your existing presets. If your freqtweak rc files are in the default location ( ~/.freqtweak/presets ) just execute the script with no arguments, otherwise specify the directory containing preset dirs as the first argument.

Get the source code and build it yourself here.

Actually, I recommend downloading the latest CVS version and building from that:
	cvs -d:pserver:anonymous@freqtweak.cvs.sourceforge.net:/cvsroot/freqtweak login
	cvs -z3 -d:pserver:anonymous@freqtweak.cvs.sourceforge.net:/cvsroot/freqtweak co -P freqtweak

Alternatively, you can get prebuilt binary packages for various RedHat distros at Planet CCRMA.
Or you can get some Debian packages here.

FreqTweak supports manipulating the spectral filters at several frequency resolutions (64,128,256,512,1024,2048, or 4096 bands) depending on your needs/resources. Overlap and windowing are also selectable.

The GUI filter graph manipulators (and analysis plots) have selectable frequency scale types: 1x and 2x linear, and two log scales to help with modulating the musical frequencies. Filters can be linked across multiple channels. The plots are resizable and zoomable (y-axis) to allow precise editing of filter values.

The current processing filters are described below in the order audio is processed in the chain. Any or all of the filters can be bypassed. The state of all filters can be stored or loaded as presets.

  • Spectral Analysis -- Multicolor scrolling-raster spectrogram, or energy vs. freq line or bar plots... one shows pre-processed, another shows post-processed.
  • EQ Cut/Boost -- Your basic multi-band frequency attenuation. But you get an unhealthy number of bands... Note that this EQ is not intended for mastering purposes, it allows for (and doesn't protect against) highly irregular filtering. Two versions, one does only frequency gain cut, the other boost.
  • Pitch Scaling -- This is an interesting application of Sprengler's pitch scaling algorithm (used in Steve Harris' LADSPA plugin). If you keep all the bins at the same scale, it is equivalent to Steve's plugin, but when you start applying different scales per frequency bin, things quickly get weird. For highest quality results (at the expense of transients) use larger FFT (>= 1024 bins).
  • Gate -- This is a double filter where a given frequency band is allowed to pass through (unaltered) if the power on that band is between two dB thresholds... otherwise its gain is clamped to 0.
  • Delay -- This lets you delay the audio on a per frequency-bin basis yielding some pretty wild effects (or subtle, if you are careful). A feedback filter controls the feedback of the delay per bin (be careful with this one). This is basically what Native Instrument's Spektral-Delay accomplishes. Granted, I don't have all the automated filter modulations (yet ;). See their website for audio examples of what is possible with this cool effect.
  • Limit -- This is very harsh brick wall limiter on a per-bin basis. It is not very pleasant, but can be interesting.
  • Compressor -- This is a massively multiband compressor. It will not behave quite like a normal time-domain compressor because of the inherent block processing of the FFT. Each frequency bin has its own compressor complete with Threshold, Ratio, Attack/Release time, and makeup gain. This is *not* suitable for mastering applications!
  • Warp -- This one is a little different, both axes represent frequency, and the identity matrix is unaltered audio. Changing the value (height) of a bin, reallocates the energy at that frequency to the new frequency bin represented by the height of the bar. For instance, if all bins are the same height, all the frequency energy is added to a single bin. This is a sensitive filter, the Log frequency scale is helpful here (it affects both axes).

Modulators to an filter can be attached from the Modulations Window (Control->Modulators... Ctrl-M). Add a modulator by clicking on the Add Modulator... button and select from the choices. To attach a modulator to a filter, click on the Attach... button on the modulator panel and pick a filter. You can modulate many filters simultaneously. The text entry fields can be used to exactly set the slider values, by pressing enter/return after entering the number.

The following modulators are currently implemented, with more to come soon.

  • Rotate -- This will continually shift a filter horizontally at a constant definable Rate, wrapping when it reaches the edge. The edges are definable with the Min and Max Freq controls.
  • Rotate LFO -- The same as the above, except the shifting rate oscillates via LFO with its own Rate and Depth controls. Currently there are sine, triangle, and square waveform shapes. The frequency range that the modulator affects is definable with the Min and Max Freq controls.
  • Value LFO -- Shifts the values up and down with an LFO. The depth control here is percentage of total value range. The frequency range that the modulator affects is definable with the Min and Max Freq controls.
  • Randomize -- Randomizes the bin values between the given value bounds (as percentages of total range). Again, the frequency range that the modulator affects is definable with the Min and Max Freq controls.

  • JACK -- providing realtime low-latency audio interconnection and delivery. JACK requires the ALSA Linux sound drivers so you'll need those too. If you haven't used JACK before please study the Linux Audio User Guide and make sure to read the section on JACK.
  • FFTW -- for speedy FFT processing (compiled as single-precision). v2 and v3 supported.
  • wxWindows (wxGTK) -- the GUI toolkit I've chosen to use. It should work with versions at or above 2.6.x. I haven't tested with the 2.4.x in a while.
  • libsigc++ 1.2 -- this library is usually already on recent systems, but if not get it and install it.

Mouse Control
  • Left button click/drag to draw filters. If Control is down, the y-axis is fixed at the last cursor location (to draw nice horizontal lines). If Control and Alt are down you can draw nice arbitrary straight lines.
  • Right button drag to move filters around in space. The filters wrap around the left/right edges unless you hold down Control. Dragging with both left and right buttons down moves both primary and alternate together (on Gate).
  • Holding Shift modifies the alternate filter (on double filter graphs like Gate) for the previous operations.
  • Middle-button pops up frequency axis menu.
  • Ctrl-Alt right-click resets a filter to default values.
  • Shift-Ctrl-Alt Left-Drag zooms in on the y axis. Look at the status bar to see the values for the cursor itself and the values of the filter at the cursor's frequency. Shift-Ctrl-Alt Right click-release resets the Y-zoom to full.
  • The B and BA buttons mean Bypass and Bypass All respectively.
  • The L and LA buttons mean Link and Link All respectively.
  • The G and GS buttons mean Toggle Grid and Toggle Grid Snap respectively. The right button can be used on the Grid buttons to choose the grid resolution.

Here is an example of using freqtweak with an alsaplayer feeding it and output going to speakers (alsa_pcm:out_?) without using a JACK patchbay:
Start freqtweak first with this command line:

  freqtweak -n ft &

Then start alsaplayer like so:

   alsaplayer -o jack -d ft:in_1,ft:in_2 &

  • MIDI/OSC control of filter and modulators
  • non-GUI version

Please address questions, bugfixes, etc to the mailing list at freqtweak-user@lists.sourceforge.net
The SourceForge project page is http://sourceforge.net/projects/freqtweak

Created by Jesse Chappell <jesse at essej dot net>

Last modified: Wed Jul 7 23:25:28 EDT 2004

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