Can you explain this? Do you mean that BASIC programs were encoded as sound in some way, and then could be uploaded into the computer and run?
The tape would contain bleeps and blurps which would be decoded into bytes by the computer. EG this is the sound produced by an Amstrad cpc464 loading a game: https://www.youtube.com/watch?v=OvChkOHgDIo
This meant that to copy software you didn't even need a computer, just a double cassette deck.
And that by recording the credits of this BBC show to tape and playing that back into the computer you'd load some program. That's actually a brilliant idea, I wonder what kind of software they broadcasted.
Sounds (pun not intended but noticed) like steganography.
Software has even been distributed on vinyl records and flexi singles!
You could connect a domestic cassette recorder up to a BBC Micro and use to save and load software onto normal cassettes!
There were favoured devices that would give better results and better cassettes for data storage and so on.
Its all ancient history and folklore now :-)