Baudline

The baudline time-frequency browser is a signal analysis tool designed for scientific visualization. It runs on several Unix-like operating systems under the X Window System. Baudline is useful for real-time spectral monitoring, collected signals analysis, generating test signals, making distortion measurements, and playing back audio files.
License.
Baudline binaries are available for free download. The binaries may be used for any purpose, though no form of redistribution is permitted. Source code is available for purchase under a number of licenses. While the Baudline website states that the source code is dual-licensed, under both a proprietary license and a version of the GNU General Public License, no source code released under this dual-license is made available for download on the software's website nor has been shown to exist elsewhere.