High-resolution audio files have become popular recently. These are files that offer resolution (I’ll explain that in a minute) greater than what is available on CDs. A CD contains music in what is known as the “Red Book” format, 2 channels, 16-bit linear PCM (pulse-code modulation), sampled at 44.1 kHz.
High-resolution files are available at higher bit rates and sample rates than what you can get on a standard CD. These may be 16-bit at a higher sample rate, 24-bit at the same sample rate, or, most often, 24-bit at a higher sample rate. The most common high-resolution audio files are 24-bit, 96 kHz, but sample rates up to 192 kHz exist as well.
Bit and sample rates available depend on how the music is recorded. For example, you may see files at 24-bit, 88.2 kHz; this is because 88.2 kHz offers the most mathematically pure way of downsampling audio to the 44.1 kHz required by the CD format. Some recording systems use a sample rate of 176.4 kHz – four times the sample rate of CDs – and it makes more sense to simply divide that sample rate in half than to downsample it to 96 kHz, which would introduce more artifacts.
(Note that you can also get high-resolution files on optical discs, such as DVD-audio discs or SACDs (Super Audio CDs), but I’m only discussing digital files here.)
Many Mac users listen to high-resolution files using iTunes or other software, and it’s important to note that to get the most out of these files, you need to check some settings. First, iTunes supports high-resolution files, in its Apple Lossless format. (See Why iTunes Doesn’t Support FLAC Files for a discussion of Apple Lossless and FLAC files.) While you can play them in iTunes, you may not be playing them at their full resolution, because the sound card in your Mac may not be working at the correct sample rate.
And there’s the rub. I’ve heard from many people who are delighted with their high-resolution audio files, who actually aren’t listening to them at their full bit and sample rates. And even some vendors of high-resolution files don’t even tell Mac users what they need to do. I looked at HDtracks’ Frequently Asked Questions, and they make no mention of changing the bit and sample rate on a Mac (or on a Windows PC for that matter).
So here’s what you need to do. Go to your Applications folder, then open the Utilities folder inside it. Open Audio MIDI Setup. Click on the output you’re using for your music – in most cases this will be Built-in Output, and may be Analog or Digital.  (You may have specific hardware connected to your Mac to play music; if so, choose that in the source list.)
Check the Format settings. If they’re set to 44100.0 HZ and 2ch16bit Integer, then you’re listening to high-resolution files at CD quality. Change these to 96000.0 Hz (regardless of whether your high-res files are 96 kHz or less) and 2ch-24bit Integer. Close the app. Your sound card will now play these files at their correct bit and sample rates. 
(Some people will argue that oversampling will make lower-resolution audio files sound worse; I don’t think so, but if you do, you can make the above change only when you play high-resolution files.)
So, tell me the truth… If you listen to high-resolution files on your Mac, had you already changed those settings? If you’d read my Macworld article of 2011, you most certainly did. But otherwise, this information isn’t easy to find. If you do listen to high-resolution files, then you should make the change now.
- Current Macs have hybrid analog/digital outputs. The digital output is a Toslink connector that is limited to 24-bit, 96 kHz. ↩
- If you stream high-resolution files via to an Apple TV or AirPort Express, then you won’t get high-resolution audio; they’re limited to 16-bit, 41.1 kHz. I understand that HDMI may go up to 192 kHz, but I don’t see this on either of my Macs. You may also be able to get up to 32-bit, 384 kHz audio via USB, with certain adapters. iTunes won’t be able to play that sample rate, though; you’ll need other players for this. ↩