In principle they can, in practice the limitations on processing power have caused the sounds they produce to lack the richness of analog. They're getting bette

In principle they can, in practice the limitations on processing power have caused the sounds they produce to lack the richness of analog. They're getting better though. The thing about analog is that you get a lot of random variation in the waveforms. A naive computer implementation will lack that variation. A better one will purposely add particular random variations. The really good ones, like Diva (which runs on a regular computer), will run SPICE-style simulations of the actual analog circuitry, but running that at full fidelity is still pretty processor-intensive. There are lots digital hardware synths that emulate analog. There are also hybrids, like Novation's Summit and Peak. These start with digital sound generation, but using FPGA to run at a much higher sample rate (24 MHz instead of the typical 48 to 96 kHz). Then they convert to an analog signal that runs through analog filters, then they convert back to digital for effects (reverb and such). The advantage of starting with digital here is that it can start with different waveforms than the ones easily generated by analog circuits. Further muddying the waters, modern analog synths have components with a lot more precision than in the old days, so they also lack some of the random variation of the old stuff. That's great for staying in tune, but now synths like the OB6, which is pure analog, have added "vintage" features which artificially add the variations again.