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RWTH ASR - The RWTH Aachen University Speech Recognition System


RWTH ASR (short "RASR") is a software package containing a speech recognition decoder together with tools for the development of acoustic models, for use in speech recognition systems. It has been developed by the Human Language Technology and Pattern Recognition Group at the RWTH Aachen University since 2001. Speech recognition systems developed using this framework have been applied successfully in several international research projects and corresponding evaluations.

RASR consists of several libraries and tools written in C++. Currently, Linux (x86 and x86-64) and Mac OS X (Intel) platforms are supported.



The development of RASR is ongoing. A Manual is available in the RASR Manual Wiki. Access to the wiki requires registration.

Publications about the theoretical foundations and methods used can be found in the publications page. The software package is described in detail in Rybach et al. The RWTH Aachen University Open Source Speech Recognition System. Interspeech 2009.

A short introduction is given in these slides.

Please post questions in the support forum.


RASR is available only in source form. See the included README for build instructions.

A set of installed tools and libraries is required (Debian package name given in brackets):

Terms of Use

RASR is free software; it can be redistributed and/or modified under the terms of the RWTH ASR License. This license includes free usage for non-commercial purposes as long as any changes made to the original software are published under the terms of the same license. Other licenses can be requested.


Remark: No acoustic or language models are included.

To download the software, you have to accept the license terms. Please fill out the form. The information submitted is only for internal usage and will not be given to third parties.

I agree to the terms of the
RWTH ASR License
I want to use the documentation wiki. Username, password, and a confirmation link will be sent to the given e-mail address.
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To demonstrate a large vocabulary system we offer the following models (in a binary format) developed for our EPPS English system together with a ready-to-use one-pass recognition setup: The acoustic model was trained using the TC-STAR English Training Corpus. The language model was trained using the Final Text Editions provided by the European Parliament and the transcriptions of the acoustic training data.

Terms of Use

All offered materials may be used for research purposes. Any commercial use is prohibited. Whole or partial distribution of the data provided is not allowed.

Publications of results obtained through the use of original or modified versions of the data have to cite the authors by refering to the following two publications:

J. Lööf, C. Gollan, S. Hahn, G. Heigold, B. Hoffmeister, C. Plahl, D. Rybach, R. Schlüter, and H. Ney: "The RWTH 2007 TC-STAR Evaluation System for European English and Spanish". In Interspeech 2007, pages 2145-2148, Antwerp, Belgium, August, 2007.

D. Rybach, S. Hahn, P. Lehnen, D. Nolden, M. Sundermeyer, Z. Tüske, S. Wiesler, R. Schlüter, and H. Ney: "RASR - The RWTH Aachen University Open Source Speech Recognition Toolkit". In IEEE Automatic Speech Recognition and Understanding Workshop (ASRU), Hawaii, USA, December 2011.

To download the demo system, please fill out the form below. We will send you an email about how to proceed with the download.

I agree to the terms of use