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This README file covers the 2005-01-01 pre-release of the Postfish by
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Xiph.Org.

>>>> What is the Postfish?

  The Postfish is a digital audio post-processing, restoration,
  filtering and mixdown tool.  It works as a linear audio filter, much
  like a rack of analog effects.  The first stage of the filter
  pipeline provides a bank of configurable per-channel processing
  filters for up to 32 input channels.  The second stage provides
  mixdown of the processed input audio into a group of up to eight
  output channels.  The third stage applies processing filters to the
  output group post-mixdown.

  The Postfish is a stream filter; feed it audio from a list of files
  or input stream, and it renders audio to standard out, as well as
  optionally providing a configurable audio playback monitor via a
  sound device.  If the input audio is being taken from files,
  Postfish also provides simple forward/back/cue seeking and A-B
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  looping control.  The next major update of Postfish will also
  include automation to allow mixdown settings to be 'recorded' and
  applied automatically during rendering.
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>>>> What is the Postfish for?

  The Postfish intends to include exactly and only the most useful
  basic filters needed to produce a good mixdown from audio recorded
  'in the field'.  The filter set also comprises the fundamentals
  needed for master mixdown in a small studio.  It is not an editor;
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  for that reason, it is intended to be used with an audio editor such
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  as Audacity.

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  If, for example, you've just multi-tracked a rehearsal of your
  troupe's current rock opera and the Director then appears out of
  nowhere (they always do) and says "Have a mix ready for my review by
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  morning", the Postfish is all you need.

  Or, as another example, you've recorded for a band who'd like to put
  out a CD of the live performance...  All the band FX are already in
  the multi-track, so the Postfish plus Audacity is all you need.

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  In a studio, tracks usually get recorded dry, so there's generally
  multiple mixdown stages of adding effects.  Postfish (obviously)
  does not give you a large array of instrument or situation-specific
  effects and it never will.  What it does give you is the effects
  necessary to take the tracks from earlier mixing and produce preview
  mixes and final masters.  Of course, if you already have $100k of
  analog rack... you likely won't be using Postfish.  If you don't
  have that rack already, Postfish means you won't need it.
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>>>> What effects does the Postfish include?

Declipper:

  The Postfish declipper is a 'build audio from scratch'
  reconstruction filter. Any section of audio exceeding a configured
  amplitude threshold is marked 'lost' and the filter builds new
  audio to fill the gap. In this way it can be used to repair both
  digital clipping that occurred during sampling, as well as analog
  clipping that may have happened at an earlier stage.

Single-band compander:

  A single-band compander is used to compress, limit, expand, or gate
  an input signal, thus providing basic dynamic range manipulation
  abilities.  

  The Postfish single-band compander provides independent over and
  under threshold controls for each channel, each providing expansion,
  compression, attack, release, lookahead and soft-knee configuration
  for three independent over, mid and under tracking filters.  Each
  filter may also be configured to track by peak, or track by RMS
  energy.

Multi band compander:

  The Postfish multi-band compander is similar to the single-band
  compander above, and provides all of the same controls with an
  addition: each over/under threshold is configurable by full-octave,
  half-octave or third-octave bands, for up to 30 bands of independent
  companding for each of 32 input channels and the group of eight
  outputs.

  The multi-band compander includes a global 'mid' compand slider,
  like the single-band compander.  This slider acquires a new use in
  multi-band mode however, where it can flatten or expand the dynamic
  range of an entire channel (or the entire recording) without
  any artifacts.

Equalization:

  30 band -60/+30dB 1/3-octave beat-less EQ per input channel and full
  output group.

Deverberator:

  Live recordings have a tendency to end up with too much reverb,
  especially when one is forced to use ambient miking.  The
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  deverberator dries out overly 'wet' live signals.  Also good for
  taking unwanted room echo out of speech recordings.
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Reverberator:

  ...for adding reverb to signals that are too 'dry', especially to
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  even out apparent stage depth when mixing close miked signals (like
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  vocals) to an ambient-miked signal.

  The Postfish provides a stereo reverb per input channel and a mono
  reverb per output post-mix.

Limiting:

  Simple, old-fashioned causal output hard-limiter to avoid unexpected
  digital clipping on the output.  Configurable by threshold, knee
  depth and release speed.

Mixdown:

  Postfish provides both a master attenuation and delay panel (which
  places these basic sliders for all channels on one window) as well
  as per-input mixdown that allows each input channel to be multiply
  routed to one or all of eight output through an additional cascade
  of four additional independent attenuation/delay/invert units per
  input, as well also allowing each input to be mixed through a
  'crossplacer'.

  The crossplacer is used to place any input into a stereo [or
  greater] image by altering not only the relative attenuation across
  channels (the 'cross attenuate' control), but also by adjusting
  phase and delay across channels (the 'cross delay' control).  The
  A-B slider then controls how far the input apparently images toward
  the A output bank or the B output bank.  

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  The direct mixdown blocks allow additional manual control over the
  input->output matrix; the direct mixdown blocks run in parallel with
  the crossplacer and all may be active simultaneously.

  Of course, with eight output channels, one can begin
  imaging/mastering for more than just stereo...
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>>>> Don't we already have several free apps that do this sort of thing?

  The short/wrong answer is maybe. The complicated answer is no.

  .) I needed a specific set of filters
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  .) I needed them in one place working together 'out of the box' 
  .) I needed to instantly hear changes I made to settings as I made them
  .) I needed to be able to absolutely trust the filters 
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  .) I needed it all to be convenient to use

  Given my specific requirements, nothing else came close to filling
  the niche and I didn't want to cobble together a 90% solution out of
  multiple other apps when this functionality was the very core of
  what I needed for mixdown.

  Both the Postfish UI and the filter functionality are intended to be
  the most usable day-to-day set, rather than sporting the maximum
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  number of buttons in the smallest space, pack in more features than
  the next app, or sport the slickest 'skin'.
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  Postfish is the way it is because I need it, and I use it for the
  core basics of mixing that I absolutely cannot afford to screw up.
  Some filters (like the declipper and deverberator) are unique.  Even
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  among those that aren't, Postfish deliberately sets speed/quality
  tradeoff much higher than most existing apps.
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  The multiband compander is a case in point; other free apps
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  implement this effect. To my knowledge, all use the simplest/fastest
  method, operating directly on the FFT of a windowed block.  An
  FFT-based multicompander is fast, but the aliasing and frequency
  multiplication artifacts (you eventually end up multiplying the
  input by the transfer function of the window shape; most noticeably,
  they tend to cause odd pitch changes in raw vocals) render them
  unsuitable for professional-quality work.

>>>> What does the Postfish require?

  .) Linux 2.x (ports come later) with OSS or ALSA OSS emulation
  .) Libraries: FFTW3, pthreads, Gtk2
  .) Gcc and gmake
  .) A sound card or external USB/Firewire A/D/A
  .) A video card, preferrably one with fast AGP
  .) Alot of CPU.  Really.  As much as you can throw at it.  Dual Xeon 3GHZ?  
     Yup, you can use all of it.

  Seriously, this is a very CPU hungry app because of the
  aforementioned speed/quality tradeoff.  I can do simple mixdown of 8
  channels to stereo with a few effects in realtime on my G3-400, but
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  the machine is crying.  My dual Athlon 2600 keeps up much better,
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  but it's still possible to overwhelm it by lighting up all the
  effects and feeding it enough input channels.  The declipper,
  especially, eats CPU on heavily damaged audio.  The multiband
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  compander is runner up in 'absurd levels of CPU usage'.  If you
  don't have fast AGP video, the EQ panel alone will probably kill
  your machine.
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  Postfish, BTW, is designed to scale to multiple CPUs.  A dual
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  Athlon/Pentium/UltraSparc/PowerPC runs Postfish much better than a
  single processor.

>>>> Why is this a pre-release?

  Because it's not finished.  A few things are more obvious than others:

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  1) A number of panels are still unimplemented.  These are the only
     inactive features on the UI, but they're right on the main panel.
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  2) Postfish *should* be a JACK-able app, but isn't.  That too should
     be done for a real release.

  3) Although the whole thing is designed as a rendering engine
     wrapped up in a neat async-safe library that's then used by an
     asynchronous UI, the source isn't entirely arranged that way.  It
     should be.  It will be for final release.

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  4) This code is just now seeing light of day.  It is probably *full*
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     of simple bugs.  I'm confident in the audio pipeline itself (I've
     hammered on it mercilessly) but there's certainly many UI
     interconnection bugs left to find.

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  5) The automation robot isn't there yet.  Right now a user has to
     frob knobs in realtime to make settings adjustments during a
     render.  That's not really acceptible.  All teh setttings changes
     must be preprogrammable; they will be.

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  6) Everyone knows a release requires documentation.  There is no
     documentation.

>>>> There's no documentation!?

  Not yet; good documentation requires effort and time.  

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  That said, if you read the list of effects, knew what they were, and
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  knew basically how to use them, you should be able to pick up the
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  Postfish and do useful work in a few minutes of playing around.
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  I took care to establish and follow conventions in the UI: If you're
  using the shipped postfish-gtkrc theme, square blue buttons turn
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  things on.  Triangular blue buttons pop configuration windows.  

  (If you're running a nonstandard system-wide Gtk2 'theme' that skins
  a set of custom widget renderers into Gtk, well, I'll let you deal
  with figuring the convention out as I use a number of custom widgets
  subclassed from 'stock' Gtk and so you'll see a mixmash of classic
  Gtk and your skin.  Sorry, no way around it other than to purpousely
  defeat your 'theme' which you probably won't like either.)
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  The grid of buttons on the right in the 'channel' frame are the
  effects for the input channels.  The square blue buttons turn a
  specific effect on for a specific channel.  A triangle pops the
  configuration for that effect.  Mixing controls are labelled
  "Atten/Mix" in the lowest row in the "channel" panel.

  Further right is the "master" panel; these controls work the same
  way for effects on the output channels after mixdown.

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  Finally, postfish -h will tell you how to get audio in and reroute
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  audio out.

  Only two things are probably impossible to figure out just from
  an afternoon of playing around:

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  1) When Postfish starts for the first time, all input channels are
     mixed into the center of a two channel output.  If, for example,
     the input is already two stereo channels and the output should be
     the same, the proper mixdown configuration is to go to the
     mixdown panels for channel 1 and channel 2 and then set input
     channel 1 to mix only into output channel 1 and input channel 2
     to only output channel 2.
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  2) Turning "Atten/Mix" off for any channel will mute it completely
     in all input effects, not just in the mixdown (this obviously
     doesn't affect output, but it also silences all the VU meters for
     that input channel, and that can be disconcerting if you don't
     expect it).

>>>> How do I get, build and install it?

  Postfish is in Xiph.Org's Subversion repository.  Get the source using:

    svn co http://svn.xiph.org/trunk/postfish postfish

  Edit the Makefile to select the proper 'ADD_DEF' line.  LinuxPPC
  users want the first, almost everyone else wants the second.  It
  should be self explanatory given text in the Makefile.

    cd postfish
    make

  and as root,

    make install

Happy hacking (and mixing),

Monty
TD, Xiph.Org