Sound Tools Extended (STx) is an acoustic speech and signal processing application for Windows. It provides tools to analyse, visualise, segment, and annotate wave files. It uses it's own annotation file format, but can import and export PRAAT TextGrid files. The software is actively being developed at the Acoustics Research Institute in Vienna, and is used in a variety of acoustic fields around the world. For non-commercial, scientific and educational purposes, we offer STx free for download.

Brief Description

Signal Processing

STx incorporates a sophisticated sound analysis and signal processing package:

  • frequency analysis based on Fast Fourier Transformations (FFT)
  • spectrum estimation methods, e.g. autoregressive (AR), Pseudo-Wigner distribution
  • fundamental frequency and formant frequency extraction, e.g. cepstrum, linear predictive coding (LPC)
  • digital filtering
  • the windows WAVE format is the standard soundfile for format (8-32 bit, 1-128 channels, up to 250 kHz sampling rate, PCM or float)

Graphical Analysis

STx can display signal analysis in the following forms:

  • spectrogram/sonogram
  • waveform
  • waterfall plot
  • function plot

Programming Language

All functionality available in STx is also available in a dedicated programming language.  Additional applications can be easily programmed in this language (either by the end user, or the Institute). STx also includes a command line interpreter and a sophisticated debugger. Using script file programs, STx can be used in batch mode for:

  • automated sound analysis procedures
  • interactive experiments
  • test designs
  • automated signal and process control.

Interface Protocols

STx supports the following protocols from within the scripting language:

  • DDE
  • DCOM

An STx/DDE/DCOM demo application is currently available for Microsoft Excel and the statistics software package "R".



  • creates, imports and exports MS Windows WAVE files.
  • runs on Windows all commonly used Windows versions (Windows 7 - 10) and under Wine.
  • stores its metadata in XML files.


STx metadata format (segment addresses, attributes and parameters) is compatible with archiving systems and requirements, since it is stored in an additional file alongside the original wave file.These files can easily be imported into an archiving database system.