Recommendation ITU-T P.501 describes test signals which are applicable for several purposes in telephonometry. This Recommendation gives a wide variety of test signals starting with low complexity test signals up to test signals with a high degree of complexity incorporating a lot of typical parameters of speech. Besides technical signals such as sine waves or noise, more speech-like signals are described. This Recommendation describes the principles of the signal construction for each type of test signal. Characteristic properties such as power density spectra, probability density functions or shaping filter responses are shown. This Recommendation gives an overview about the typical application of the test signals described. This overview is a guideline giving general application rules. The detailed description of the application however should be found in the individual Recommendations describing the measurement procedures for a certain application. In order to avoid problems in creating the test signals described, all these test signals are freely available for download from the ITU-T test signals database. Annex A proposes two test signals (a pn-sequence with a low crest factor and a logarithmically distributed multi-sine wave) for the measurement of terminal coupling loss (TCL). Annex B provides speech files and noise sequences to be used in combination with objective speech quality evaluation methods. This speech material does not replace the speech material found in Supplement 23 to ITU-T P-series Recommendations. Annex C provides a description of the processing applied to the speech signals in Section 7.3.