Create Mindstorms NXT Speech Sound Files    Send article as PDF   
FreeAudioEditorGive your LEGO Mindstorms NXT Robots a Voice, by creating New LEGO Mindstorms NXT Sound Files for them! This process is very easy, thanks to some Freeware Audio Editing software and some perseverance on your behalf.

To get started, download a copy of Free Audio Editor for MS Windows and install it. To produce the NXT ‘RSO’ sound file required by the LEGO NXT Brick, you will also need a copy of Dave Baum’s “Wav2Rso“, or his latest version of BricxCC with full support for the LEGO Mindstorms NXT brick which has a ‘Wave-to-RSO’ converter built in!

Bricx Command Center (BricxCC) is a Windows (95, 98, ME, NT, W2K, XP, Vista) program commonly known as an integrated development environment (IDE) for programming the RCX (all versions), Scout, Cybermaster, and Spybot programmable bricks using Dave Baum’s Not Quite C (NQC) language. And it supports programming the Scout, RCX2, and Spybot using The LEGO Company’s MindScript(tm) and LASM(tm) languages via the Mindstorms 2.5 SDK. It supports programming RCX bricks in C, C++, Pascal, Forth, and Java using the brickOS, pbForth, and leJOS alternate firmwares. BricxCC now also supports programming the new LEGO Mindstorms NXT brick using Not eXactly C (NXC), Next Byte Codes (NBC), and a simple on-brick programming language called NPG.



To begin creating your custom Speech files for your NXT Robots, start up Free Audio Editor and you should end up with the following screen.

Free Audio Editor 2011 ( Edit audio files visually; Record audio from a microphone or any other available input device; Apply various effects; Burn audio CDs from MP3, WMA, WAV, and OGG; All in one program, simple and intuitive

From the File Menu, select ‘Text-to-Speech‘.

Free Audio Editor 2011 ( Creating Text-to-Speech Audio Files

Enter the Text for the Speech you wish to create into the “Synthesise Speech” box. Select your preferred Voice, and then click the Synthesise Speech button to create the sound file as below.


You should end up with a visualisation of Sound File in the main edit window like below. It pays to remove the excess silences at the beginning & end of the file. Just click & drag the mouse pointer to select the area to remove. Next hit the ‘Delete’ key to remove the area.

Free Audio Editor 2011 ( Editing Audio Files

When you have finished editing the file it’s time to save it as a “wave” file. From the File Menu, select ‘Save As..‘.

NOTE: You will need to save the file as a 8 Bit, 8000Hz, Mono wave (.wav) file, to insure the smallest file possible as shown below!
  To be able to convert your newly created file to an NXT (.rso) file, the wave file must not Exceeds 64k in maximum size.

Saving File

For a wider selection free Voices to use, try AT&T Labs Natural Voices® Text-to-Speech Demo page where you can download the outputted audio from the text as a mp3 file which converted with Free Audio Editor and saved as a wave file.

Now you have your custom .wav audio file it is time to convert it with Dave Baum’s “Wav2Rso“. Run Wav2Rso.exe and you will end up with the following program window.

  1. Click the ‘Directory‘ button, to select your preferred working directory for the output LEGO Mindstorms NXT ‘RSO‘ files.
  2. Click the ‘Select‘ button, to select your wave file you just made, ready for conversion.
  3. Select ‘Linear‘ from the list and set ‘Rate‘ to 8000, & tick the ‘Compress‘ box.
  4. Now Click the ‘Convert‘ button to built your NXT ‘RSO‘ file. Now Click the ‘Convert‘ button to finish.

Now you should have your new Voice file in RSO format to suite your LEGO Mindstorms NXT Brick, ready for your Robot to communicate with. You will need to use LEGO Mindstorms NXT-G Software, or use a program like NeXTExplorer shown below, to download your RSO file to the NXT.


Download Dave Baum’s NeXTExplorer, which is a Windows program that lets you explore files on the NXT and PC with drag-and-drop support between the two systems. You can execute programs on the NXT, play sounds on the NXT, defragment the NXT filesystem, delete selected files or all files, and much more. This is a standalone version of the NXT Explorer tool built into BricxCC.

You may wish to Download the RSO Sound Files I used for my Tic-Tac-Toe Playing Robot: 66.2Kb to experiment with as well if you wish? Here as well is a collection 17 Colour 26.8Kb in RSO file format which may be of interest?

All the Software used above to produce LEGO Mindstorms NXT compatible RSO Sound files, will happily run on a MS Windows XP Guest, using VirtualBox on Linux or Mac machine!

I personally run a 32Bit MS Windows XP Guest in VirtualBox on my 64Bit PC, running amd64 LinuxMint as my Operating System. The MS Windows XP Guest will also happily Run all my 32Bit MS Windows based LEGO Mindstorms Software, including LEGO’s NXT-G, & Digital Designer software, plus BricxCC, RobotC, too name just a few.



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