Just as video standards have gone from SD to HD to 4K, audio has also seen drastic improvements in quality. Now high-res audio is the order of the day for those who want the very best listening experience.
iPhones don't arrive with this as an immediate option, but with an app or two - and perhaps some expensive new headphones and a DAC - you can make it a reality. In this article we show how to listen to high-res audio on your iPhone.
What is high-res audio?
It's a marketing term that refers to better-than-CD recording quality.
One important aspect of the quality of a track is the sample rate. This determines how many times a second the original source material is captured, and the amount of dynamic range.
On a CD the values of these two will be a sample rate of 44.1kHz with a bitrate of 16bit. High-res audio offers substantially more with 96kHz and 24bit, so there is increased detail to work with on those tracks.
Some online music stores now plug high-resolution files which claim to go well beyond even CD audio, although, when you look into it, also beyond the limits of human hearing. You'll see music listed as 24/96, which means 24bit/96 kHz. A larger bit depth results in higher potential dynamic range capture within a specific slice of time, while the frequency refers to the sample rate - the slices of audio captured per second. So 96 kHz audio is sampled more than twice as much per second as 44.1 kHz audio.
Naturally, the assumption with bit depth and frequency is that larger numbers are better. One thing they certainly are is larger, and this extends to file sizes. If you thought Apple Lossless, FLAC and AIFF audio files were big, high-resolution audio equivalents will seem gargantuan; single albums can easily clock in around the 1 GB mark.
The snag is that 16bit audio deals ably with what people can hear, and so it's hard to make an argument in favour of higher-resolution audio at the best of times, let alone when you're dealing with mobile devices that have limited storage.
Which music format should I use?
Audio can be lossy or lossless. Compressed lossy files (such as MP3 and AAC) have long been the norm in digital. They essentially approximate a raw music file, attempting to discard 'irrelevant' data that people cannot hear, resulting in a smaller file size, but losing information along the way.
This is similar to how you can take a high-res scan and then turn it into a compressed JPEG. The trick is in finding the right balance between file size and ensuring the original content isn't degraded to the point differences in quality are overly noticeable.
When ripping CDs in iTunes, the Import Settings within General Preferences determine the encoding used. Options include MP3, AAC, AIFF and Apple Lossless (ALAC). AIFF will result in files that sound identical to the original source, but these will be huge: about 10 MB per minute.
On a Mac with a boatload of storage, this might be OK, but mobile devices are more limited. Unless you only want a tiny selection of music on your iPhone, AIFF is not a good bet. Apple Lossless is compatible with the iOS Music app and will generally take up about half as much space, but sound identical to the original CD. It's a better bet.
Do not entirely dismiss compressed lossy audio. Using the iTunes Import Settings dialog, you can fine-tune the level of compression for these formats when CDs are ripped, matching iTunes Plus for AAC (256 kbps, although you can go higher) or setting the bit-rate of MP3 all the way up to 320 kbps.
Even at their maximum settings, the resulting files will be significantly smaller than AIFF and Apple Lossless. However, at higher bitrates, which discard less information, the vast majority of people won't be able to hear any real difference between AAC/MP3 and the original CD source.
Find out if you can tell the difference between high- and low-quality audio here.
Apple offers a selection of music on the iTunes store called Mastered for iTunes, which is a step up from standard MP3 or AAC as it involves remastering the tracks to avoid some of the pitfalls that accompany digital compression techniques. But even here there is some lossy compression involved, so it remains something of a compromise.
Lossless files include FLAC, ALAC (or Apple Lossless), and DSD. All of which boast CD-quality sound or better... and come with enormous files sizes.
Where to find high-res audio files
Another thing to bear in mind is where you download music from, if CDs are something you consider should be consigned to history. iTunes sells 256 kbps AAC, and 320 kbps MP3 is commonplace elsewhere online. (The two are roughly comparable.)
However, if you bought or downloaded MP3s many years ago, they may be at a much lower bit-rate (128 kbps, say); while most people find it difficult or even impossible to tell the difference between modern iTunes Store downloads and CD audio, 128 kbps removes too much of the original data and can sound noticeably muffled, compressed, tinny, or just plain bad.
Where possible, get newer versions of your files. If you've got a ton of them, consider buying iTunes Match for a year. There are tutorials online about how you can match (an admittedly fairly well organised) iTunes library, delete your local files, and then replace them with shiny new 256 kbps AAC from Apple.
High-res versions are often more expensive than the standard iTunes alternatives. When we were preparing this article, Radiohead's remastered OK Computer OKNOTOK album was available for £9.99/$13.99 as a Mastered for iTunes edition, or £19 for a high-res audio version on HDTracks.
Just remember that you'll need to download any high-res files on your PC or Mac rather than the iPhone itself.
You can also set up iTunes so that it imports higher-quality versions of the tracks of any CDs you might buy. To do this, launch iTunes and go to iTunes > Preferences > General, then select Import Settings and in the Import Using dropdown menu, choose Apple Lossless Encoder.
Another option is to sign up to the Tidal HiFi music service, which offers a high-res streaming option for £19.99/$19.99 per month.
How to play high-res files on your iPhone
Buying high-res audio tracks is one thing. Playing them is another. iTunes and the Apple Music app don't support FLAC or DSD files, so you won't be able use them without re-encoding the files in the Apple Lossless (or ALAC) format or downloading a compatible app.
Importing to iTunes
If you've bought and downloaded FLAC or DSD files from one of the sites listed above, or indeed any other you find, you'll need to import them into iTunes before Apple's Music app can see them. But because iTunes doesn't like FLAC files, they'll need to be converted first.
You can find a number of converters online or in the App Store. FLACTunes FLAC Converter, for instance, has very positive reviews and is a snip at £0.99/$0.99.
Download the app of your choosing, then it will be a case of simply adding the tracks you want to convert and then setting the output format as Apple Lossless or ALAC.
When this is done, go to iTunes on your PC/Mac and click File > Add to Library.
A Finder window will appear. Navigate to your high-res files, select them and click Open.
The tracks will then be entered into your library, so the next time you sync your iPhone or if you use iTunes Matching you'll be able to access them on your device.
Using a third-party app
If you don't want to go through the whole converting process, and don't mind using an app other than Apple Music, then there is an easy way to get the high-res files on your iPhone.
VLC for Mobile is a free app that's always an excellent choice. It might not be fancy, but it gets the job done.
If you want something with a bit more polish, and don't mind spending £9.99/$9.99 on IAPs to access the high-res audio features, then Onkyo HF Player is the one to choose.
Before you begin moving files, make sure the music you want is downloaded to your PC/Mac. Now, open the desktop version of iTunes, and plug the iPhone into your computer.
Click on the little iPhone icon that appears at the top of the page and you'll be presented with the general summary screen for your device.
Select Apps from the menu pane on the left side of the page, then scroll the right pane down until you see the File Sharing section.
Under here there should be the music app that you downloaded. Click on it and then in the Documents section just to the right, click on the Add button.
From the finder window that appears, select your high-res audio tracks and click Add.
Now click Sync to move them onto your iPhone, and when this is completed click Done.
To listen to your tracks all you need to do is open the app and the files will be there.
Beyond ensuring you're not trying to play audio compressed so heavily it sounds like it's coming from a transistor radio someone threw in a hedge in a garden half a street away, the main difference you can make in improving your iOS audio experience is purchasing new headphones.
Macworld has a roundup of alternatives to Apple's bundled headphones. Even twinning a 30-quid pair of headphones with reasonably high-quality lossy audio will greatly improve what's going into your ears. To a point, though, you get what you pay for, at least up to a few hundred pounds, and so if you can budget a bit more for headphones, your inner audiophile will be happier.
Note that the type of headphones you go for will also impact on audio quality. Over-ear headphones ('cans') tend to be better than earbuds, although they're of course significantly bulkier. Bluetooth wireless headphones have improved a lot in recent years, but still tend to offer inferior sound quality than wired equivalents, and for a higher price.
Will my headphones work with high-res audio?
Here's the rub.
The apps discussed above will play the tracks, you'll hear them in your headphones, but if you're using the 3.5mm headphone jack they won't be any different to normal standard tracks: that jack doesn't output high-res audio.
The Lightning port is capable of supporting this feature, but at the moment the only real way to get high-res audio from your phone is to use headphones that have a built-in high-res DAC - you should check out our guide to the best Lightning headphones for more ideas.
In a home setup, you'll again find spending a bit of money helps improve the sound coming out of your device. Often, small speaker docks offer mono rather than stereo output and are essentially the speaker equivalent of cheap earbuds.
More expensive speakers designed for mobile can be better (read: Best speakers for iPad and iPhone) but you must still remain mindful of those only capable of outputting a compromised signal when it comes to the stereo image. When possible, consider buying a hi-fi amp and speakers for a home or office system and connecting your iOS device to that.
Note: don't get taken in by snake-oil claims regarding cabling; it's one thing to pay a few hundred quid for a decent set of speakers, but anyone splashing out the same on a cable to connect their iPhone to their amp is a mug.
Is high-res audio worth it?
This guide is a starting point. There are countless pieces of kit and countless opinions about how you should experience audio. It's a very subjective field, and so we'll finish with a few thoughts.
First, don't feel bullied into buying a lot of kit because you think you should. Second, where possible try 'blind' tests, to check different headphones and speakers out on music you enjoy. You may find a £50 pair of headphones is fine and - to your ears - no worse than the £200 pair. Similarly, do some blind tests on file compression, because there's no point in re-ripping your entire music collection to Apple Lossless and desperately cutting down the albums you can store on your iPhone if it turns out you can't tell the difference between such files and the same music encoded as 256 kbps AAC.
Also be mindful that a lot of modern music is mastered in a manner that means a lot of nuance has been lost, regardless of the technology you throw at it. (Do a web search for 'loudness war' for more information.) Things are slowly changing, but no amount of careful ripping and perfect headphones will save recorded audio designed to punch your ears in.
And finally, realise that compromise is inevitable to some extent when dealing with mobile. iOS devices are limited in terms of storage and technology, and so your aim shouldn't necessarily be the best audio experience ever, but one that you consider good enough for the effort you make and the financial outlay you can happily afford.
Craig Grannell contributed to this article.