A portable computer like the Amstrad PPC 640, released in 1988 has no ISA expansion ports, he has only a feeble speaker. So you may think it isnt possible to get some nice sound except of simple beeps ?
On the Amstrad CPC it was possible to have a better sound using a Digiblaster sound card connected to the parallel port. It was a simple electronic device with several resistors, not difficult to make in fact.
Well, there is the same thing on PC since ages : the Covox Speech Thing.. It is possible to buy a Covox 4 on Serdashop which is an upgraded version of the Covox Speech Thing (higher precision resistors : 0.1% and low pass filter). For more informations about the Covox, I recommand reading the related articles on Nerdly Pleasures.
I also bought the MCE2VGA on Serdashop which lets you use a VGA external screen instead of only using the internal screen which is quite lacking.
The software used here is Mod Master XT beta 18 by FreddyV which you can download on Vogons.