Using a PC In Lieu of a Cassette Recorder
Knut Roll-Lund has written a utility called PlayCAS which allows for the use of a PC as a cassette player for a TRS-80 Model I/III/4 Level I and II.
You simply connect your TRS-80 cassette input to your PC soundcard (if using a standard TRS-80 cable plug the plug that normally goes into the ‘Ear’ output of a CCR-8x into the PC’s headphone jack). When you then run the PLAYCAS utility, you can CLOAD (or SYSTEM) on the TRS-80 and feed it an emulated CAS file.
PLAYCAS supports 250 Baud (Level I), 500 Baud (Level II), and 1500 Baud (Model III) and supports SYSTEM (Machine Language), CLOAD/CSAVE (Level II BASIC), EDTASM (Editor Assembler), and Level I BASIC and Machine Language.
PLAYCAS v1.2 (2012) can be downloaded here