[linux-audio-user] Announcing initial release of FreqTweak

Jesse Chappell jesse at essej.net
Sun Oct 13 13:34:26 EDT 2002

Announcing the initial release of FreqTweak (v0.4)


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 spectragrams and energy vs
frequency plots displaying both pre- and post-processed spectra.

It currently relies on JACK for low latency audio interconnection and
delivery.  Thus, it is only supported on Linux.

FreqTweak is an extremely addictive audio toy, I have to pry myself
away from playing with it so I can work on it!  I hope it has value
for serious audio work too (sound design, etc).  The spectrum analysis
is pretty useful in its own right.

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

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 spectragram,
       or energy vs. freq line or bar plots... one shows
       pre-processed, another shows post-processed.

    EQ -- Your basic multi-band frequency attenuation.  But you get
       an unhealthy number of bands...

    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.

    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.

Have fun... report bugs...

  Jesse Chappell <jesse at essej.net>

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