I’m currently listening to some music through iTunes on my Mac. It’s playing through a set of powered, external speakers (Klipsch).
This means I have three volume controls to deal with: the iTunes application volume control, the Mac OS X systemwide volume control, and the physical volume control knob on the external speakers.
If optimal audio quality is my goal, how should I set the volume at each of these stages? Should I max out iTunes and OS X, and use the speaker to control volume? Set them all to medium, then use the speaker to fine-tune? Set them all to medium, then use OS X?
I don’t know that there will be a single answer for this, but there are some things to consider:
Do you have a modern (Intel) Mac, with the little remote thingy? If so, I’d max iTunes, set the speakers to medium well, and and use the system volume as the control, because the up/down buttons on the remote will set it for you (also, the volume control buttons on your keyboard, if you’ve got a keyboard that has these).
Otherwise I’d max the iTunes volume and the system volume, and use the speaker control knob: it’s the only analog control in the bunch, so it will give you a little finer “steps,” plus its probably easier to reach.
I can’t think of any reason to use the iTunes volume separately unless you’re doing something else on your Mac and want to play tunes quietly in the background. If iTunes is the only app making noise, there’s no benefit to using both unless you’re really, really picky about your volume level (since the iTunes one is basically selecting a percentage of the system volume, and they both have a limited number of “steps”, using both gives you a smidge more control.)
Note that this is mostly an ergonomic analysis. If your speakers hiss above a certain volume, or your Mac does (a problem I have all the time on cheap Windows sound cards, but never on my Macs), you’ll want to set the offending element to the maximum acceptable volume and use something else to control. But assuming clean sound all around, I don’t know why you’d prefer one solution to another based on anything other than ease of use.
In traditional analog audio systems the rule of thumb was that most stages sounded best near their mid-range of amplification. Way low gain on one and then way high on the next to compensate would almost always sound worse then both at midrange.
But in digital, it won’t make much of a difference. It might with 8-bit PCM, since it has linear steps, but 16-bit PCM (which almost all sound is nowadays) has logarithmic steps. Unless you overload your soundcard, which I don’t think I’ve ever done, it would probably sound best to turn the digital all the way up and use the analog volume.
16-bit PCM uses linear encoding, as does 8-bit PCM on many old computers. The telephone system uses 8-bit PCM and a logarithmic scheme called mu-law encoding.
For many systems with multiple stages of amplification, the best results are produced when the gain is evenly distributed among the amplifier stages.