What does BitPerfect do? Why wouldn't iTunes/Music app already be "bit-perfect?"
The main reason I got BitPerfect is that my Mac-based iTunes/Music app library, which I have on a headless Mac mini that I use as my digital music streamer (USB out --> Oppo UDP-205 USB Async DAC in), has music files of varying bit depths and sample rates: 16 and 24-bit, and 44.1k, 48k, 88.2k, 96k, 176.4, and 192k sample rates. The Mac's digital audio output operates only at a fixed bit depth and sample rate - it cannot do on-the-fly resolution-switching. So if you go into the Audio MIDI utility and set the output to, say, 24 bit and 96k, that will work perfectly for 24 bit, 96k files. But will then take 16 bit, 44.1k files (aka CD-quality files) and resample them to 24 bit, 96k before sending them out over the computer's USB port.
At the time I first set up this system (had an Oppo BDP-105 then), I was persuaded that 100% bit-perfect output made an audible difference in the sound compared to just using iTunes and relying on the Mac's default fixed-resolution audio output setting.
These days I'm not so sure. In particular, the bit-depth thing seems like a non-issue to me: it's clear to me that the thing to do is to just set the Mac's output to 24 bit or 32 bit, since that will just pad lower bit-depth files with harmless zeroes. In fact, even though BitPerfect is, well, bit perfect, it too pads everything to 32 bit on output, as it detects that the Oppo's DAC is compatible with that.
The one area where I'm still uncertain, though, is the sample rate. I'm not terribly keen on sample-rate conversions that are not even-integer conversions. In other words, I know that upsampling a 44.1k source to 88.2k will be harmless and inaudible - such upsampling will just make a copy of every sample to double the number of samples. Same for 176.4k - that will just make 3 copies of each sample, to quadruple the rate. But when it comes to resampling between 44.1k and 48k - or even multiples thereof - then it's not so simple and I figure why do that if I don't have to?
Even there, though,
@mansr and others have demonstrated to me that 44.1k to 96k conversion is trivial and losslessly reversible, which strongly indicates that such a conversion would have no detectable sonic effect.
Still, seeing as BitPerfect is only $10 and sits seamlessly between iTunes and the Mac's audio output settings, I consider it money very well-spent.
However, if I were just setting this system up now, after having been a member here for all this time, I might not get BitPerfect. Instead, I would probably just set the Audio MIDI utility to output everything at 32 bit, 88.2kHz, and replace the 15% or so of my library music files that have 48k, 96k, and 192k sample rates with versions that have 44.1k or 88.2k sample rates.
Even as it is, I've replaced 192k and 176.4k files with 96k and 88.2k files whenever possible, as the former just take up space to no audible effect.
The only other lingering question I have is that BitPerfect, like many standalone third-party audio players, has the ability to use Integer Mode. My understanding - which could be incorrect - is that without BitPerfect the Mac will use floating-point mode, which is not technically bit perfect. But again, it might very well be that floating point output is accurate beyond the limits of what we have to worry about, so that could be a total non-issue as well. I'm sure there are folks here who know.
