Generating sound waves from PC sound card isn’t new ting. You can even download tons of software that allows generating various waves like sine, square, triangle waves on speaker output. Such sound generator gives quite good results that are acceptable in most situations like testing audio equipment or feeding complex signals in to your projects.
There are some shortcomings here. The signal frequency is limited to 20kHz which his not that bad actually when speaking about audio. And there is a risk to damage audio card. Hobbydebraj have found that it is hard to add signal offset that would allow generating signals above 0V level. So he managed to build a simple circuit based on LM358 amplifier which gives ability to add an offset. Now using Matlab software he could generate any complex signal he wanted.