If future iPhones switch to USB-C, what will that mean for their sound quality?

(Image credit: MacRumours)

Whether it’s Apple’s endgame for the iPhone or just a bridging gap towards a portless design that relies on wireless charging, it seems increasingly likely that future Apple phones will ditch the proprietary Lightning port for the more universally adopted USB-C one. Indeed, Apple has reportedly already started testing USB-C iPhones.

Rumour has it that the switch will materialise in next year’s iPhone 15 (with this year’s iPhone 14 models retaining Lightning) and that Apple accessories such as the AirPods, MagSafe Battery Pack and Magic Keyboard/Mouse/Trackpad are also in line for USB-C in the foreseeable future. After a decade of exclusively peddling its proprietary Lightning connection over USB-A, Micro USB and USB-C in its phone line-up, it seems Apple is having a change of heart – almost certainly in the face of European members of parliament voting to introduce a single charging connection for mobile phones to reduce electronic waste and consumer frustration. 

So, what will this change mean and will it have an effect on sound quality? 

The iPhone’s current state of hi-res play

If you want to play local hi-res files on your iPhone or stream them from Apple Music, you are ultimately limited by the DACs inside Apple’s devices. For the uninitiated, that’s the ‘digital-to-analogue' chips that convert the digital music on your phone to the analogue headphones you’ve plugged into your phone via the Lightning-to-3.5mm adapter.

Now, Apple’s Lightning-to-3.5mm adapter supports a maximum of 24-bit/48kHz audio (coincidentally, so does the internal iPhone DAC that it bypasses). It cannot handle and therefore output tracks of a higher quality with a sample rate of, say, 96kHz or, higher still, 192kHz. If you try and play these music files or streams through the adapter, the iPhone will simply downsample them to 24-bit/48kHz. That’s still ‘hi-res’, mind you – anything above ‘CD quality' 16-bit/44.1kHz technically is – but you aren’t benefitting from the maximum quality of your file or stream. 

You could alternatively go down the Lightning headphones route and plug a pair straight into your iPhone, but in our experience, their DACs tend to ‘only’ handle up to 24-bit/48kHz too (perhaps an Apple-stated requirement in order to be licensed). Over Bluetooth, the audio limitations are more severe due to the technology's need to compress.

At the moment, if you want to listen to 24-bit/96kHz or higher, you need an external DAC filling between your iPhone and wired headphones sandwich, end of. That could be an ‘in-line’ portable DAC like the new Astell & Kern AK HC2 Dual DAC Cable (which comes boxed with a tiny Lightning adapter) or a USB-A-ended DAC like the Audioquest DragonFly Cobalt that requires Apple’s Lightning-to-USB camera adapter to connect to an iPhone.

So, would USB-C change this? 

While there are downsides to Apple switching to USB-C, such as Lightning being a physically slightly smaller connector and therefore allowing for slightly slimmer devices, there are also benefits to the move, particularly for the consumer. USB-C cables are generally cheaper – Lightning cables can be picked up very affordably now, but they aren't often Apple ('MFi') certified; their transfer data speed is significantly faster than Lightning – 40Gbps vs 480Mbps (though it should be said that Apple doesn’t release all specifications of its proprietary technology); and they support fast-charging due to higher power delivery capability – currently you need a 20-watt adapter and USB-C adapter cable to fast-charge an iPhone. Of course, having one charging cable to fit all devices is ultimately more convenient, too. But will iPhone sound quality be affected?

Directly, no. A connection is a connection and it’ll come down to whether Apple allows the DACs inside its future iPhones and/or adaptors to passthrough higher than 48kHz sample rates uncompressed. But indirectly, the switch to USB-C could still have implications on how we consume higher quality music on iPhones.

When Apple started offering hi-res tracks on its Music service last year and it became clear that iPhones couldn’t natively make the very most of it without an external DAC, we wondered why Apple hadn’t cashed in and released its own at that seemingly appropriate time – one of a higher quality than its fundamentally crude Lightning-to-3.5mm adapter, which is essentially a DAC and low-power amplifier that arguably acts as more of an 'enabler' than an 'improver'. Perhaps the ‘Apple DAC’ pot is already brewing, waiting for the USB-C switch. Apple will surely develop its own Lightning-to-USB-C adapter to cover its billion+ legacy devices out there, but perhaps there is an opportunity for something better too.

As for existing third-party USB-C DACs, that could well be one less adapter (and bit of bulk) required for them to fit into a new iPhone – that is, if Apple allows them to play ball with iPhones from a software and power current point of view, which has been a hurdle for some supporting iPhones in the past. Apple seems to be loosening its grip, with some third-party DACs now able to get around needing Apple’s camera adapter dongle by making their own. We would, however, feel for manufacturers who have already gone the extra mile (cost- and perhaps licence-wise) to ensure their offerings are Lightning compatible.

It might be a good excuse for Apple to give its wired AirPods Max headphones a rethink, too – and the firm surely wouldn't make the same gaffe twice. As the Lightning-ported AirPods Max can only accept a digital (not analogue) signal when wired – and only using Apple's proprietary Lightning-to-3.5mm audio cable, which inherently cannot transmit audio losslessly due to its analogue-to-digital process – there's no way of listening to absolute lossless music through the AirPods Max. It seems unlikely now that Apple will create a Lightning-to-Lightning cable that can fix this for the AirPods Max – perhaps the current headphones haven't been built in a way that would allow this to happen, anyway – but we hope lossless wired listening will be doable in any successive pair.

Portless designs pose a threat

It’s hard to imagine a phone connector endgame that involves any type of socket and cable anyway. Whether it is in two years or five, Apple will inevitably move to a portless design that relies on wireless (probably MagSafe) charging, and when it does, that could be a backward move not only in terms of transfer and charging speeds but also sound quality, which could find itself at the sole mercy of Bluetooth standards. No DAC/wired headphones option to save the day for people who care!

Considering Bluetooth today does not have the data rate to support uncompressed hi-res (or even CD-quality) audio yet, we very much hope that the technology progresses to allow uncompressed lossless transmission by the time portless phones are in our pockets. Either that, or another wireless method that allows it is created instead. A freshly granted patent around a new optical audio transmission method suggests Apple is looking into it, at least...

So, should we be worried or excited? Call us optimists, but we'd side with the latter. Yes, portless designs potentially pose a threat to audio quality, but they could also be a driver of wireless audio innovation too.


How the AirPods 3 were made – and how Apple plans to make them even better

How to play hi-res music and lossless audio on your iPhone

This guy modded his AirPods to use USB-C (and you can too)

Apple Music lossless: which devices will (and won't) play lossless and Spatial Audio

Best iPhones 2022: the best budget and premium iPhones

Becky Roberts

Becky is the managing editor of What Hi-Fi? and, since her recent move to Melbourne, also the editor of Australian Hi-Fi magazine. During her 10+ years in the hi-fi industry, she has reviewed all manner of audio gear, from budget amplifiers to high-end speakers, and particularly specialises in headphones and head-fi devices. In her spare time, Becky can often be found running, watching Liverpool FC and horror movies, and hunting for gluten-free cake.

  • TobyM
    Portless design is a terrible idea. USB-C is used to charge the phone. Most use bluetooth to listen to music. What I'd want from Apple is not having to have all sorts of cables and dongles just to charge one or another device. Portless is yet another obstacle to being able to charge one of these devices with a popular easily accessible cable out there. Sticking to any forms of charging method that ultimately makes it harder for consumers to charging their device will once more demonstrate Apple is far more concerned about its greed than anything else as the cost of their own cables and dongles have already plainly made evident.
  • djh1697
    ARCAM produced a "MUSICboost" for the iphone 6/6s, which gave a great uplift to the sound of the phone. personally, I do not use it often, useful on long trips. That added some USB-C functionality to the phone, charging the battery in the boost and the phone.

    I paid less than £30 for it, it was rendered obsolete when Apple discontinued the phone. The review was 3/5 when the price was £99. I'd give it 5/5 at the lower price
    It uses the PCM1704 DAC which the Naim DAC, now discontinued, used two of them.