The book "Inside the Apple IIe" had a program to digitize voice from the cassette port (https://archive.org/details/InsideTheAppleIIe/page/n341/mode/2up https:/

The book "Inside the Apple IIe" had a program to digitize voice from the cassette port (https://archive.org/details/InsideTheAppleIIe/page/n341/mode/2up https://archive.org/details/InsideTheAppleIIe/page/n341/mode...). The results were shockingly good. I never had a IBM PC w/ a cassette port, but reading thru this article I see that EA's Music Construction Set had an option to output sound on the cassette port. It looks like the digitization method "Inside the Apple IIe" uses (looking for zero-crossings and making a 1-bit square wave approximation of the sampled audio) would work on the PC hardware.