Download the JAVA-Application AudioValveSimulator.zip (10kByte) for Windows, Mac and Linux.
If you don't have the JRE (JAVA Runtime Environment) installed then you'll get it here: http://www.java.com/de/download/manual.jsp
The application plays WAV audio files of the format 44.1kHz/16Bit through a non linear x3/2 characteristic to simulate the sound of a single valve amplifier creating harmonic distortions (limited to k2). Please keep in mind that this is a simple model to approximate the non linear behavior of a valve excluding all other parts in the signal path of a real world amplifier.
There are two parameters which can be changed during playback (update button):
1.) The operating point (Bias) of the valve
2.) The amplitude of the incoming signal (Modulation)
Because of the x3/2 characteristic choosing a low Bias (e.g. 0.3) with a high modulation amplitude (e.g. 0.2) creates more harmonic distortions (k2) than a high bias (0.8) and a low modulation (0.1).
The Bypass option allows a direct comparison between the clean and distorted signal.
A good way to experience the distortions is to use a sinus test signal of 1kHz. In that case the human ear is quite sensitive to distortions whereas in real world music examples distortions need to be much higher to be audible.
Disclaimer and License:
This Software is provided "as-is", without any express or implied warranty.
In no event will the author be held liable for any damages arising from the use of this software.
Permission is granted to anyone to use this software except for commercial use.
Please contact me if there is a wish for a commercial implementation.