iTunes isn't the only one pushing higher sampling rates. Neil Young has been pushing Pono as a platform to bring back higher fidelity to digital recordings. But for that, you've got to go back to the original tracks and remaster them at the new sampling frequency (which they are doing with Pono), or you haven't gained anything in the process.

As mentioned, upsampling means changing the sampling rate. So if you upsampled from 41kHz to 48kHz, you now have 48000 samples per second instead of 41000 samples per second. But where do those extra 7000 samples per second come from?

To a computer or media device, music is just a stream of numbers. So if you had a snippet of music sampled at some rate, it might look like this:

... .234, .300, .550, .557 ...

If this stream were upsampled to twice the sample rate, the stream would look like:

... ???, .234,???, .300, ???, .550, ???, .557, ??? ...

That is, twice as many numbers would be used to represent the same audio stream.

The computer can only guess what those values are likely to be. There are all sorts of methods which produce reasonable results (linear interpolation, cubic splines, etc.), but they're all guesses. The original information was never captured, so it can't be restored.

For example, you could linearly interpolate the missing numbers by averaging the numbers around it:

... ???, .234, .267, .300, .425, .550, .553, .557, ??? ...

So now you've got enough numbers in the stream to play it back at the new sampling rate. But you didn't add higher fidelity to the recording. To do that, you'd have to go back to the original recording and re-mix at the sampling rate.

But... If the information wasn't recorded at a higher sampling rate, the information isn't there in the recording anyway. So all your DAW can do is upsample.

That's what happens when you import tracks from BiaB at CD quality, and set your project to a higher sampling rate. Behind the scenes, the BiaB track is being upsampled.

However, all the effects and processing will be at 48kHz (possibly higher, depending on the DAW), so there is a benefit to working at a higher sample rate.

-- David Cuny
My virtual singer development blog

Vocal control, you say. Never heard of it. Is that some kind of ProTools thing?