An invention is provided for testing telecommunications devices. Broadly speaking, test data is encoded prior to testing a SUT. Then, during testing, the encoded test data is transmitted to the SUT, which processes the test data. The processed test data then is received back from the SUT. The processed test data is decoded in real-time, as opposed to the encoding of the test data, which is performed offline and prior to testing. In addition, a quality of the processed test data is analyzed. Typically, the test data is speech data, which is stored prior to testing the SUT. Optionally, the speech data can be encoded offline using a computer system separate from the testing system.