What is Hi-Res Audio? HD music explained

Heard about Hi-Res audio and wondering what the fuss is all about? We've broken down everything you need to know so you can decide if it's what your music collection needs.

Hi-Res Audio: Next-gen sound

Just as 4K and HDR have become the buzzwords of TVs, Hi-Res is the must-have standard for audio gear. You may even have noticed a little gold and black ‘Hi-Res Audio’ logo alongside some products, as if it’s an official seal of approval. But is Hi-Res Audio really such a big deal?

It can be if the conditions are right, but there’s a lot of misleading information out there, so here’s what you need to know.

What is Hi-Res audio?

Hi-Res audio describes digital audio files of better-than-CD quality. They are also higher-quality than those currently delivered through streaming services like Apple Music and Spotify. Hi-Res hardware is designed to handle these enhanced files.

In Hi-Res phones and music players, that handling is literal. Not everything can manage such audio data. But in ‘normal’ headphones and speakers, which are analogue devices, it tends to denote a frequency response good enough to let you notice the difference. In theory at least.

Before we dive deeper into what makes a Hi-Res audio track, let’s take a look at some of today’s best Hi-Res-capable gear.

Related: Best headphones

Today’s Hi-Res hardware

Top High-Res audio player: Astell & Kern AK70 MKII

Phones have almost killed standalone music players, but companies like Astell & Kern keep the category alive for the enthusiasts out there. The Astell & Kern AK70 MKII costs £599, which isn’t cheap, but it does provide audio quality far and above that available on any phone.

A quick glance makes it seem similar to one, though. It runs Android, for example, a heavily customised version that pares the software down to a music-driven UI. The difference is that the Astell & Kern AK70 MKII has a dual-DAC setup – for handling the left and right channels individually – and a more powerful headphone amp circuit.

Astell & Kern also makes much more expensive players too, which can handle 32-bit audio natively (it will be downsampled to 24-bit here) and have as much as 256GB inbuilt storage.

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Hi-Res headphones: Sennheiser HD 800 S

Look critically at the headphones companies like Sony and Sennheiser, and you’ll see a pattern. Pretty much any half-decent pair gets that special little Hi-Res logo. The £1100 Sennheiser HD 800 S  are a top-end example, but even the £170 Sony MDR-1A get the badge.

It amounts to these companies saying “we think these pairs can do justice to ultra-high quality files”, and officially means they can handle upper frequencies of at least 40kHz.

That’s far outside the realms of human hearing, which sits around 20kHz. But manufacturers will argue that headphones that cap their capabilities between 20Hz-20kHz won’t produce the frequencies at the very edges of this spectrum as well as those that exceed it.

How accurate that is is questionable. The fact of the matter is, if you have some old headphones you love, they’ll play back high-res files without a problem. How well they do it depends on how good they are, not whether they have a badge on the box.

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Questionable Hi-Res:  Sony h.ear go

Sony has pushed the Hi-Res agenda more aggressively than any other major tech pedlar, even applying it to its h.ear go £190 Bluetooth speaker. It justifies the use of the term because the speaker uses a digital amplifier and an “upscaling” DSEE HX filter designed to counteract the effects of compression.

The use of the term is somewhat disingenuous, though. Its aptX Bluetooth is not a Hi-Res signal and the sound the box produces is characterised by its use of small, compromised drivers, not any quasi Hi-Res fiddling. It doesn’t represent the spirit of Hi-Res audio, if such a thing exists, and certainly won’t playback proper 24-bit Hi-Res files.

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Hi-Res in phones: LG V30

Without a doubt, the best smartphone for audio is the LG V30. It has a 32-bit ESS SABRE 9218P Quad-DAC, which is of a standard you’ll find lurking in those high-end dedicated audio players.

It also has a 2.0Vrms headphone amp stage, almost twice as powerful as that used in the iPhone. This isn’t directly related to Hi-Res, but a great DAC isn’t going to be that useful if the amplifier doesn’t have the power to drive your fancy headphones with ease.


Hi-Res at home: Naim Mu-so

The Naim Mu-so is the ultimate in one-box hi-fi. Yes it costs £900, but what it does for the cash is nothing short of superb.

It’s an audiophile’s box of tricks, with physical connections that include USB, optical and a 3.5mm jack, but streaming smarts that include aptX Bluetooth, AirPlay and built-in Tidal support.

From a Hi-Res audio perspective, it supports playback of 24-bit/192kHz WAV, FLAC and AIFF files from a uPnP device, such as a NAS drive, as long as it’s hardwired to your router. Prefer wireless? It’ll downsample playback to 48kHz.



What makes an audio file Hi-Res?

A Hi-Res audio file needs to be above CD quality. CDs offer a 44.1KHz sampling rate and 16-bit depth. What this means is the data on a CD has 44,100 slices of music information every second, each of which has 65,536 possible gradations.

sampling

Take a look at a 24-bit/96KHz file, for example, give each slice 16,777,216 gradations, with 96,000 slices a second. There are even 192KHz sampling rates offering even more besides.

That’s a lot of numbers to take in, but put simply – the higher the bit depth and sample rate, the closer to the the original analogue audio soundwave a digital file can be. And the closer it gets, the more likely it is to sound better (though this is far from a given).

What Hi-Res hardware offers are the DACs capable of handling all this extra data. A DAC turns the digital data back into the analogue waveforms that are finally delivered to your speaker drivers, and into your ears.

What’s the minimum spec for Hi-Res quality

Back in June 2014, the major record companies finally got together to agree what the previously amorphous term ‘hi-res audio’ should mean. They came up with this definition: “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.”

This initially led to 24-bit, 96KHz becoming the baseline standard. However, in 2016 the RIAA loosened the definition a little to make Hi-Res streaming more feasible, leading to a “48kHz/20 bit” minimum standard.

Meet The Codecs

Hi-Res Audio doesn’t refer to any one format, though. It can be packaged in a number of different ways using various codecs, which are the ‘languages’ of digital audio.

The most popular suitable codecs include FLAC, ALAC, AIFF, WAV and DSD.

Here’s a quick look at the differences between these main audio standards:

FLAC – Probably the most popular lossless format, FLAC was introduced in 2001. It is an open format. Despite being lossless – which means that none of the music information is lost in the digital transition – it’ll still reduce the size of music files dramatically, much more than the older WAV or AIFF formats.

ALAC – This is Apple’s own lossless format, used in iTunes when you want to rip tracks losslessly. It’s open-source just like FLAC. So what’s the benefit of ALAC over FLAC? Audio-wise, nothing. However, iTunes – not to mention any iDevice – can’t play FLAC files, but can play ALACs.

AIFF – If you think FLAC is old, get a load of the 28-year-old AIFF. The issue here is that it’s much less space-efficient than FLAC. The files are pretty large.

WAV – Similar to AIFF, WAV is a long-standing lossless audio format, one much less efficient data-wise than FLAC and ALAC. It was created by Microsoft and IBM, surfacing in the early ’90s.

DSD –  DSD is the true audiophile digital format, created by Philips and Sony for use in Super Audio CDs (SACDs). The benefit of DSD is that sampling rates go up to an incredible 2.8MHz or 5.6MHz, which is 64 or 128 times the rate of CD. However, it does so at 1-bit depth, rather than the up-to-24-bit rate you’ll get in some of these other formats. So every time it captures audio data, it captures less, but does so with astonishing regularity. 5.6MHz DSD will eat up almost 5GB in an hour.

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As for Hi-Res streaming…

MQA — This is not a traditional codec but a container used to cut down how much data Hi-Res streams consume. It is lossy but was certified as Hi-Res-eligible in 2016. For more: What is MQA?

aptX HD — A new format for Bluetooth streaming supports up to 20-bit 48KHz data, which maker Qualcomm says is indistinguishable from 24-bit, 96KHz to the listener. For more: AptX HD: The future of high-res music streaming

Hi-Res Audio sources

Here are some of the top online spots to download high-resolution audio files. Check them out for yourself:

HD Tracks – A site offering music from a wide array of genres, downloadable as albums or, sometimes, singles. You can choose format and bit-depth/sample rate.

Qobuz Sublime  – For £219.99 a year you can stream tracks at CD quality (16-bit/44.1kHz) and download 24-bit true Hi-Res files for the price of MP3. For £349.99 a year, you can bump up the streaming side of things to 24-bit/192kHz.

ProStudioMasters – This boutique store offers a relatively small selection of albums. Most albums are delivered in a choice of FLAC and AIFF, but there’s also some DSD stuff on there.

Acoustic Sounds – An American site that’s very much US-centric in its presentation, but this is a good spot to check out DSD files if you want to give them a spin.

TIDAL – You may have heard TIDAL described as a Hi-Res music streaming service, but it actually streams mostly CD quality at present. However, there is a growing selection of albums (known as “Tidal Masters”) available for MQA streaming at 24-bit/96kHz via the desktop app only – you have to be a HiFi subscriber at £19.99/month to get access though.

Is Hi-Res Audio Worth It?

Hi-Res Audio is more accessible than it’s ever been. But is it really worth the extra cost? There’s more to consider here than just the audio files themselves.

A CD-quality file through a great pair of headphones or speakers is going to sound a good deal better than a 24-bit 192KHz file through a so-so pair. Hi-Res audio may not be the same as buying £1000 speaker cables, but at times it does get close to becoming the modern equivalent.

However, it is a reminder to check what you’re listening to. If your music collection is filled with dodgy MP3s from the days of yore, it could well be time to give your digital library a spring clean.

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