VST3 Effect from Praat — User Guide (GUI Version)

What this does

This tool lets you use any VST3 audio effect directly from Praat, but now with a full graphical interface (Tkinter) for plugin selection, parameter adjustment, preset management, and live logging — while Praat remains responsive.

The workflow: Praat script → minimal form → Python GUI (opens separately) → user adjusts → Process → Praat imports result.

Quick start

1. Install Python dependencies (once): pip install pedalboard numpy soundfile.
2. Place VST_Effect_from_Praat.praat and host_vst.py in the same folder (e.g. plugin_AudioTools/).
3. In Praat, select a Sound object.
4. Run the script. A small form appears asking for:
   • Tail seconds – extra silence for reverb trails.
   • Buffer size – processing block size (default 8192).
   • Parameters – optional initial parameter string (e.g. mix=0.5, output=0.8).
   • Play result / Save as default plugin checkboxes.
5. Click Open GUI. A dark‑theme Python window appears (this may take a few seconds the first time).
6. In the GUI:
   • Use Browse to select a .vst3 file (or type the path).
   • Click Scan Params to fetch all parameter names, min/max/default/current values – they appear in the log.
   • Adjust Tail Seconds and Buffer Size if needed.
   • Enter parameter overrides in the text field (e.g. Mix=0.6, Decay=0.9).
   • Optionally Save… current settings as a preset, or load an existing one.
   • Click Process. The log shows progress. When done, the GUI closes.
7. Praat detects completion and imports the result as originalname_vst; plays it if requested.

The GUI window (dark theme)

Input WAV   C:\Users\...\vst_input.wav
Output WAV  C:\Users\...\vst_output.wav

VST3 Plugin  [ C:\Program Files\Common Files\VST3\ValhallaSupermassive.vst3 ]  [Browse] [Scan Params]

Tail Seconds  1.5   Buffer Size  8192

Plugin Parameters
name=value, name=value  (leave blank for plugin defaults)
[ Mix=0.6, Decay=0.9 ]

Preset: [ ]  [Load] [Save…]

Log
>>> Loading plugin...
>>> ValhallaSupermassive loaded.
>>> Available parameters: ...

Ready

[Cancel]  [▶ Process]
    

GUI sections

• I/O info – read‑only display of input/output WAV paths (set by Praat).
• Plugin selection – entry field + Browse button + Scan Params button.
• Numerics – Tail Seconds (spinbox), Buffer Size (combobox with common values).
• Parameter field – text entry for comma‑separated assignments; syntax name=value or name value.
• Presets – dropdown of saved presets, Load / Save… buttons (saved to ~/.vst_host/presets/).
• Log panel – scrollable text area showing all messages (parameter dumps, warnings, progress).
• Status bar – colour‑coded (amber = working, green = done, red = error).
• Action buttons – Cancel (closes GUI, no result), Process (starts processing).

Detailed workflow & threading

Praat side

• After you click Open GUI, the script writes the input WAV (vst_input.wav in Praat’s plugin directory).
• It launches host_vst.py --gui ... as a background process (using start /b on Windows, & on macOS/Linux).
• Praat then enters a polling loop: every second it checks for a sentinel file (vst_done.txt). Meanwhile, Praat stays fully responsive – you can edit other objects.
• When the sentinel appears (written by Python on exit), Praat imports vst_output.wav and renames it.

Python GUI side

• The GUI loads the last‑used plugin path from ~/.vst_host/settings.json (if any).
• Parameter scanning uses a background thread to avoid freezing, but the actual VST3 plugin is loaded on the main thread – many VST3s forbid cross‑thread loading.
• When you click Process, the plugin is loaded (if not already) and rendering occurs on the main thread. The log updates during processing.
• On completion, the sentinel file is written, and the GUI closes automatically (after a short delay).
• If you press Cancel or close the window, the sentinel is written anyway (empty result), so Praat’s polling stops cleanly.

Parameter handling & presets

Parameter string syntax

• Separate assignments by commas (spaces optional).
• Each assignment: name=value or name value.
• Parameter names are case‑sensitive – use exactly as shown by Scan Params.
• Values must be numbers (floats). Booleans are set as 0.0 or 1.0.
• Unknown names are ignored with a warning.

Scan Params button

Click this after selecting a plugin. It loads the plugin, retrieves all parameters, and prints a formatted table in the log:

  Name                                              Min       Max    Default    Current
  --------------------------------------------- ---------- ---------- ---------- ----------
  Mix                                                   0         1       0.25       0.25
  Decay                                                 0         1       0.85       0.85
  Size                                                  0         1        0.5        0.5
    

You can then copy the exact parameter names into the parameter field.

Presets

Presets are stored as JSON files in ~/.vst_host/presets/. They contain:

• plugin_path – full path to the .vst3
• tail_seconds, buffer_size
• param_string – the exact parameter text

Use Save… to store current settings under a name; Load recalls them.

Installation & dependencies

Python packages

pedalboard is Spotify’s VST3 host. On Linux you may need additional system libraries (see pedalboard docs).

Files

• VST_Effect_from_Praat.praat – the updated Praat script (GUI‑launcher).
• host_vst.py – the new GUI‑enabled Python script (must be in same folder).

Configuration

Settings are saved in ~/.vst_host/settings.json. This includes:

• plugin_path – last used plugin
• tail_seconds, buffer_size, param_string

The Praat script stores a plain‑text mirror of the last plugin path in plugin_AudioTools/last_plugin.txt to pre‑fill the form.

FAQ / troubleshooting

Command‑line usage (legacy)

The Python script still supports the old CLI mode without GUI:

Add --gui to launch the graphical interface.