I notice that some devices on the market have a discrete number of volume levels (e.g. the iPad, the Nintendo DS), whereas others have a continuous slider (or so many volume levels that it amounts to the same thing). What are the pros and cons of each approach? How much do users care about actually fine-tuning the controls? How should I decide "how many levels are enough"? To what extent do sliders actually control to users wanting fine-tuned control of the volume, as opposed to just being a convenient way of setting a ballpark?
I know the answer to a lot of those questions is "it depends" - of how much they care about the sound (doorbell vs. home cinema), what kind of interface manipulation you have (touch buttons sort of mean you have to have discrete controls, as does voice command) ... I'm wondering if I'm missing anything, and whether there are studies about the level of control people actually like.