Everything you need to know about USB-C audio
Music. It’s an immutable part of the human condition, having filled public and private spaces alike for millennia.
However, it’s only in the last couple of decades that we’ve truly been able to take the music we love anywhere we go. The technology to store and playback music has advanced beyond our wildest dreams, moving from the bulky Walkman and skipping Discman to tiny MP3 players and smartphones connected to web streaming services.
Yet the technology we use to actually listen to music seems stuck in the past. There are those who defend the 3.5 mm headphone jack with admirable gusto, yet this connector has been around for more than half a century.
Meanwhile, a superior audio protocol and connector is starting to take the world by storm. In this article, we explore how the audio interface has evolved to where it is today, and why the USB Type-C standard is poised to drive headphone innovation into the foreseeable future.
The 3.5 mm headphone jack was developed in the 1950’s as a miniature version of the even older 6.35 mm jack used in analog telephone switchboards. It didn’t hit the consumer market until the 1960s when Sony used it in their portable transistor radio (the EFM-117J), and finally reached commercialization when Sony then introduced it to the company’s legendary Walkman in 1979.
Thanks to the growing ubiquity of portable music players, headphones using the 3.5 mm headphone jack were included with Sony’s Discman, Nintendo’s GameBoy, and Apple’s iconic iPod. Over a 25-year span, nearly every portable entertainment device that was released shipped with a 3.5 mm headphone jack.
Enter the mobile phone era. Early “multimedia” phones like the Nokia 5510 could play MP3s and used an even smaller connector, the 2.5 mm jack, yet another miniaturization of the analog connector. Many devices featured this 2.5 mm jack, much to the chagrin of music lovers who had to buy an adapter to listen using regular 3.5 mm headphones.
It was rare for audio manufacturers to build headphones with a native 2.5 mm headphone jack. Along the way, several phone manufacturers also introduced proprietary connectors that only worked with their own branded headsets. Sony Ericsson was notorious for this.
Regardless of the shape or form of these connectors, they all operate on the same basic principles that’ve been around since the dawn of the electrical age. But recently, a new challenger in the form of USB-C has emerged. This connector eschews the ancient architecture in favor of a digital-centric approach, offering superior sound quality while also ushering new functionality.
The principal reason why USB-C headphones sound better than regular 3.5 mm headphones is rooted in the way the signal is processed. To understand this we must touch on a crucial element of the audio experience: the digital to analog conversion.
Unlike vinyl records or cassettes, digital music files are made up of bits of data, or “1s and 0s” as the analogy goes.
In order for any digital player (phone, tablet, laptop, etc) to output sound that can be picked up by the human ear, the device employs a DAC, or digital-to-analog converter. (DAC is often pronounced like “jack”.)
So, a DAC is embedded in your music player, a signal conversion happens, analog frequencies are sent over the 3.5 mm headphone jack, through your headphone’s wiring, and out the drivers (mini speakers) plugged comfortably into your ears.
The trouble with the above structure lies in the analog cable run. For headphones, this is the length of the cabling between the 3.5 mm headphone jack and your drivers. The greater the distance an analog signal has to travel, the more susceptible it is to degradation. Headphone cables are no different. Even specialized tuning and using expensive materials won’t combat the loss of sound quality as a cable gets longer.
In contrast, digital signals have unique characteristics which help prevent quality loss due to outside interference. Digital signals are made up of numerous discrete, or separate signals that each correspond to a “sampling” of the original sound. (That’s what it means when you see that a sound file has a sample rate of, for example, 44.1 kHz - the original sound is sampled 44,100 times per second.)
This sampling of data (made up of 1s and 0s), is not affected by interference like more “physical” analog signals. Any noise that can disrupt the signal will only show up as a nearly-indiscernible dropout, or will be corrected by the receiver circuitry. Ultimately, this means that digital audio signals can travel a much longer distance without experiencing any loss in audio quality.
A quick recap:
The solution to better sound quality is to minimize the length of the analog cable run. Thanks to their innovative structure, this is exactly what USB-C headphones with a built-in DAC do.
When you plug a pair of premium USB-C headphones into your phone, the phone’s internal DAC is bypassed so the digital signals travel all the way to the headphone’s built-in DAC.
From here, the headphones’ built-in DAC performs the usual digital-to-analog conversion, but a much shorter analog cable run is needed to reach the headphone drivers. This greatly reduces the potential for signal degradation, and is the biggest advantage of USB-C headphones.
Even though digital audio over USB-C is the way of the future, compatibility across devices remains an issue. For example, one of our testing labs told us that they tested Google’s USB-C headphones with a Huawei phone using the Amazon Music app, and the app would crash whenever the Play button is pressed. This happens because Google’s USB-C headphones are tested to be compatible with their own Pixel phones, but not designed to be compatible with other USB-C phones such as Huawei’s. Why?
Each phone manufacturer implements USB-C audio in a slightly different way so not every USB-C headset performs as expected.
*When using the Amazon Music app on the Huawei phone with our Mythro C headphones plugged in, no issues were reported.
Pro tip: choose a set of USB-C headphones with wide compatibility and firmware updates so the headset can be updated to support new devices.
In addition to better sound quality thanks to its digital format, USB-C headphones offer a variety of other advantages.
Not all phones, apps, and USB-C headphones work together in the same way. Follow the steps below to test for compatibility.
If at any point your headphones do not work (or work with one phone but not another), write down the task you were performing, the app you were using, and the resulting behavior. If the error happens during a call or system sound test, then it’s probably a fundamental compatibility issue and you’ll want to report it to the manufacturer.
It’s important to keep the firmware of any of your devices updated, and this holds true with your USB-C headphones. Firmware updates may include bug fixes, better signal processing for fewer dropouts, and most importantly, improved compatibility with more devices.
To update your USB-C headphones, connect them to your phone and open the associated app like Moshi’s Digital Audio app. From here, you can download updates to the earphones and install them automatically.
Yeah, what about wireless? Why not take the wire out of the equation entirely and use Bluetooth?
Even if we mentioned the battery issue above, sound quality is still among the most important considerations we’ve had, and Bluetooth, on paper, sounds like a good idea. After all, you’re still sending the digital signals over to a separate DAC. In fact, with Bluetooth, you have even shorter wires than USB-C headphones, right?
The answer is that Bluetooth just doesn’t sound as good as a wired connection, and this fact is pretty well-known.
Standard Bluetooth headphones use a protocol known as A2DP, in which your phone compresses the sound before sending it wirelessly to your Bluetooth headphones. If you’re listening to sound that’s already compressed, such as an MP3 file or a Spotify stream, with Bluetooth you’re applying yet another compression layer, further reducing sound quality.
More recent and high-end Bluetooth headphones use a new protocol, Qualcomm aptX, which features much more efficient compression and thus better sound quality, but it’s still a lossy way of getting sound to your ears. On top of this, both devices - phone and headphones alike - need to support aptX, or else you’ll be stuck with A2DP.
Finally, no matter what Bluetooth audio protocol you use, the amount of processing that needs to be done on both ends - decoding wireless signals, encoding audio, etc - introduces a large amount of latency, or lag, to the equation. You’ll see this in the form of bad syncing between video and audio when watching something with Bluetooth headphones.
Newer protocols are coming to Bluetooth, such as Qualcomm’s own aptX-HD and Sony’s LDAC, which promise 24-bit audio at even higher bitrates and less compression. Even if they’re considered lossy, the sound quality is too high for most people to even tell the difference.
Unfortunately, aptX-HD support isn’t widespread across headphones or earphones. Even fewer phones support LDAC as well. It will take some time before these protocols gain widespread acceptance.
USB Type-C on-ear headphones
USB Type-C earphones