mleghorn
Thanks everyone for you ideas. I'll stick with ASIO4ALL - 4 - now :-)
My computer isn't doing any A/D conversion. I have one analog device that I use occasionally (Microbrute). For that I use a Tascam interface to do the A/D. Other than that, I only use VSTs. As for D/A conversion, I hope my computer isn't doing any of that either, since I'm using the optical out of my sound card to my Headphone Amp/DAC.
The Tascam interface doesn't have a digital out, so I don't use it as an output device.
ALL audio stored on a computer is in digital format, and when you play back an audio file, whatever program is playing it back converts that digital format into analog signal that then gets routed to the speakers. In the same way, when you record, the software you are using to record converts the analog signal (vocals through mic, guitar plugged in, some instrument plugged in), into a digital stream that is then saved on the hard drive.
so, analog/digital and digital/analog conversion happens all the time when working with recording software.
The thing is that if you are using something like ASIO4ALL to simulate the ASIO drivers of an actual audio interface, all of that conversion (both directions), is handled by your computer's CPU. This isn't an issue for playing back an audio file such as an MP3, but when you get into multiple tracks in Sonar, with effects and soft synths and all that, this becomes too much for the CPU to handle very quickly, and THIS is when you start getting dropouts and crackles and pops and noise.
So, now days, dedicated audio interfaces exist, and the drivers for these route the files to dedicated circuitry in the audio interface, that performs all of that processing-intensive conversion to and from analog and digital, and it frees up the computer's CPU for doing other things, and having such an audio interface should eliminate problems with dropouts and crackles and pops and such.
So that is what I meant by analog/digital conversion (actually both directions). That is all happening for you behind the scenes, but it is indeed taking place on your computer when you work with Sonar.
One of these dedicated audio interfaces can be purchased brand new, starting around $125-$150, on up to more than $500, depending on features present on the interface (number of inputs and outputs, phantom power, supported sample rates, quality of converters). Many of the lower-end costing interfaces still have decent quality converters - they just maybe only allow 2 ins and 2 outs, versus some that allow 8 ins and outs etc.
Just make sure whenever you DO decide to get one, that you check to make sure they have software drivers for Windows 7 and hopefully Windows 8.
I hope I explained the above better this time - sorry for any confusion,
Bob Bone