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(Pocket-lint) - If you've ever listened to a CD recording of your favourite album next to a stream from Spotify or Apple Music, you may well notice a difference. That's because the quality of the recording on the CD is significantly greater than the compressed stream, particularly when you're listening to your stream over Bluetooth. 

High-resolution audio aims to give you CD-like, or better than CD-sound, in the convenient package of streaming from your phone or as a digital file on a dedicated player.

Tidal is perhaps one of the most well-known services to offer hi-res audio when it was bought by Jay Z. However, other providers have upped their game and now both Spotify and Apple Music offer higher quality "HiFi" or "lossless" audio. 

So if you're wondering what the difference is between hi-res and high-fidelity sound, allow us to explain.

Why is music compressed?

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Before we get into high-resolution audio, let's start by discussing compression.

It's no secret that the music industry went from physical formats (like vinyl) to digital formats (like MP3s), but most people don't realise sound quality was impacted during that transition due to a demand to make music files smaller. Simply put: they're easier (and cheaper) to distribute to consumers who download or stream.

In order to make a music file smaller, it must go through either lossless or lossy compression. With lossless compression, all original data from the music file can be restored after it is uncompressed, whereas lossy compression permanently reduces the music file by cutting out some data during the encoding process.

Whenever any data is lost or removed from a music file during compression, the resolution is negatively impacted. If you want to hear the difference between lossless and lossy, check out Tidal's excellent demonstration here.

What is high-resolution audio?

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There's no universal standard for high-resolution audio, which is also called hi-res audio or HRA, though The Digital Entertainment Group (in conjunction with the Consumer Electronics Association and The Recording Academy) has published the following formal definition for the term:

  • Hi-res audio is: "Lossless audio that is capable of reproducing the full range of sound from recordings that have been mastered from better than CD quality music sources."

Now, when music is digitised for downloading and streaming purposes, it is basically broken down into a series of audio snapshots (sort of like how several still frames make up a film), and our brains interpret all these snapshots together as continuous sound. The more snapshots taken, the more detail a digital music file will have.

We won't get too scientific - but just know that sampling rate is the number of snapshots taken per second when analogue sound waves are converted into digital. There's another aspect called bit depth. It's the amplitude of the waveform at each sample point (8-bit has 256 levels for each sample; 16-bit has up to 65,536 levels).

So, to recap: hi-res audio refers to audio files that have a higher sampling rate and more bit depth than a CD (and it is generally best to have the highest combination possible). A CD has a sampling rate of 44.1kHz and a bit depth of 16-bit, while hi-res files have a sampling rate typically ranging between 96kHz and 192kHz at 16- or 24-bit.

Now, let's talk about bitrate. It refers to the number of bits - or the amount of data - that is processed over a certain amount of time. So, in audio, it means kilobits per second. An iTunes song has 256 kilobits of data stored in every second of a tune. Like sampling rates and bit depths, it's better to have a higher bitrate.

But if you download a high-res file with a high bitrate, it'll naturally take up more space on your computer.

What are some hi-res file formats?

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There are several high-resolution audio file formats available with incredible sampling rates and bit-depths. Two of the most popular types are FLAC (Free Lossless Audio Codec) and ALAC (Apple Lossless Audio Codec), both of which are compressed but claim to hold onto and recover every single bit of data from a file.

Other file formats you may have seen that are considered hi-res include WAC, AIFF and DSD. 

Tidal offers something called "high-fidelity sound", which it described as "music files that have not been compressed down". That's not entirely true. Tidal streams FLAC audio files. They're compressed, as we mentioned earlier, and designed for efficient packing of audio data so that (in theory) no information is lost.

FLAC files on average have a sampling rate of 44.1 KHz, a bit depth of 16-bit, and a bitrate of 1411Kbps. CDs also have a bitrate of 1411kbps, while "lesser-quality" MP3s have a bitrate of 320kbps. (For reference: the chart above compares file format bitrates offered by Tidal, Spotify, and iTunes.)

Which services offer hi-res audio?

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Tidal, of course, is one streaming service that offers high-fidelity audio for £19.99 per month. It has a catalogue of 25 million tracks and streams at 1411kbps. Tidal works with up to 35 platforms as well, including Android and iOS. 

Apple Music offers CD quality (16-bit/44.1kHz), Apple Music Lossless (24-bit/48kHz) and Hi-Res Lossless (up to 24-bit/192kHz). Spotify HiFi is expect to launch at some point this year as well, and will offer "CD quality". 

Qobuz is both a music streaming service and download store. It offers high-resolution audio music streams in 16-bit/44.1kHz FLAC. The hi-res tier costs £19.99 per month, and you can listen to your music through the Qobuz apps for iOS and Android devices. It's also integrated with Sonos, Samsung, and Astell & Kern hardware.

Here's a list of other streaming services and download stores that offer high-res audio files:

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  • HDTracks
  • Naim Label
  • Linn Records
  • Onkyo Music
  • Bowers & Wilkins Society of Sound
  • PonoMusic
  • 2L
  • 7Digital
  • Gimell
  • HD Klassik
  • Deezer Elite
  • Technics Tracks


Writing by Elyse Betters. Editing by Adrian Willings. Originally published on 8 May 2015.