Basically a DAC connected on the LPT port. It could be implemented as an R2R DAC:

Finished result:

Then use any software that supports Covox:

Reference

• http://hackaday.com/2014/09/29/the-lpt-dac/
• https://blog-frantovo-cz.translate.goog/c/307/DAC%20%28zvukov%C3%A1%20karta%29%20pro%20LPT%20port%20a.k.a.%20Covox?_x_tr_sl=cs&_x_tr_tl=en&_x_tr_hl=en