Like Apple’s AirPods, Doppler’s Wireless Earbuds Got Delayed. Here’s Why

Both Doppler Labs and Apple announced new wireless earbuds to ship for this holiday season, and both ended up delaying their products.

Doppler’s Here One buds were scheduled to be available in November. But Doppler didn’t feel confident that it could ship a product that worked perfectly in the vast majority of cases. On November 22, it announced that it was pushing its launch into early 2017.

Apple announced its AirPods along with the iPhone 7 back in September and originally planned to ship them before the end of October. Then the company postponed that launch, saying only this: “We don’t believe in shipping a product before it’s ready, and we need a little more time before AirPods are ready for our customers.” Today, it announced that the buds were now available at Apple.com and are making their way to customers and select Apple stores.

In general terms, the two companies’ engineers have been wrestling with some of the same technical challenges.

Doppler’s Here One earbuds occlude—plug up—your ear canals, then use two outward-facing microphones, one internal microphone, and some sophisticated software to amplify certain sounds, such as a specific voice in a noisy restaurant. Or they can selectively suppress sounds like baby cries and jet engine rumbles. All this is controlled through an app, allowing you to “mix your world.” The company is also doing deals with partners such as the New York Mets, Coachella, and JetBlue to stream context-sensitive audio that you can hear without blocking out the world around you.

For Doppler, the shipping delay isn’t related to all the fancy sound layering and noise cancelling features, but rather to the more basic problem of making sure the user’s smartphone connects with both earphones immediately and consistently, even when the phone is tucked in the user’s back pocket. Apple, Doppler suspects, has been dealing with the same broad issues.

Doppler CEO Noah Kraft told me that the value of moving from wired earphones to wireless models is obvious and inevitable, but that many people underestimated the technical challenge of making it work well. “The number-one gripe of consumers is Bluetooth connectivity, the connection of the earbuds with your phone,” Kraft said.

After getting a demo of the prototype Here One earbuds, I sat down with Kraft, Doppler’s director of product Matt Jaffe, and the company’s director of software and electrical engineering, Nitin Khanna, to talk through the reasons behind the Here One delay.

Doppler is working with an undisclosed manufacturer in China to produce its earbuds. That involves producing small batches of products, then moving in phases to larger production runs, then finally going to mass production. The Doppler people say they’re now entering the final stage before real-deal mass production of shippable devices—known as the “production validation” phase—and will reach full mass production mode in January.

The Latency Problem

Lots of factors can cause too-high failure rates in production, but my conversation with Kraft, Jaffe, and Khanna focused on problems relating to latency—that is, the lag time between the millisecond when audio data leaves a phone or other source device and the millisecond when the sound is heard in the user’s ears.

For stereo audio, the left and right stereo audio signals must issue from the earphones’ speakers harmoniously and at the same time. I have personally heard another wireless earphone product fail to do this; It sounded like the mix of the music was messed up, with bass parts trapped in the right channel and certain mid-range frequencies far more dominant than they should have been.

For video viewing, the accompanying audio channel must stay perfectly in sync with the moving picture on the display. Khanna told me humans can hear latency above seven milliseconds. If lag time between the device and one or both of the earphones is more than that, the user is exposed to an unsettling sensory experience.

“With Bluetooth streaming, no users are cool with that,” Kraft says. “If you release a product with too much latency, you basically scar the product for life.”

Getting this timing and synchronization right isn’t easy. That’s because in many wireless earbuds (including Doppler’s Here One and Apple’s AirPods) the source device communicates directly with only one of the buds. That master bud must pass the audio signal on to the slave one on the other side of the user’s head, making sure the playback is in sync.

The source device’s operating system can make allowances for latency between the source device and the master earbud, but it can’t do much about the latency in that second hop from the master bud to the slave.

Doppler uses Bluetooth to connect phone to earbud, then a wireless technology borrowed from the hearing aid industry called NFMI (Near Field Magnetic Induction) to connect one bud to the other. “All the frequencies used in Bluetooth are absorbed by water,” Khanna told me. “And the space between one’s ears is predominantly water.”

The NFMI signal is more resistant to absorption by the water within the human skull, Khanna adds. So the signal moves from one bud to the other faster and latency is diminished. NFMI also increases the range such that audio data can travel for people with larger heads.

The company that makes the NFC chips in iPhones for Apple Pay, NXP, also manufactures the NFMI chip used in Here One. “While other technologies utilize a direct link through the wearers head, NFMI creates a body area network, essentially creating a bubble around the wearer,” said NXP VP and general manager Asit Goel in an email to Fast Company. “This network leads to better privacy and results in more reliable and higher quality stereo signal.” (NXP is now being acquired by Qualcomm, which Doppler sees as a validation of the NFMI technology.)

Contrary to recent reports, Apple’s AirPods do not each connect separately to the source device. Rather, they connect with a master AirPod, which then synchronizes the audio signal with the other AirPod. The details of the connection between the two AirPods remain fuzzy, but Apple probably uses a special form of Bluetooth. Part of the job of the new W1 chip in the AirPods is likely to orchestrate the connection between the two buds and the device, and to reduce latency.

Technologies At Odds

The two legs of the journey from host device to ear—phone to master earbud, master earbud to slave earbud—do not work independently of each other. Quite the contrary. The two wireless technologies can end up fighting against each other, Khanna says.

Doppler’s engineering team had to do a lot of work to get the Bluetooth and NFMI technology working well together. Part of the problem is a phenomenon called de-sensing, Khanna explains. The Here One buds are very small, only 22 millimeters wide. In such close quarters, one electronic component (like an NFMI radio, for instance) can desensitize the performance of another electronic component (a Bluetooth radio, for example) located nearby.

Doppler’s original goal was to build Here One so that one bud could connect to the other across 17 centimeters of head width. In June it upped the goal to 19 centimeters, so that people with larger heads could use the product too, Kraft said.

But just when the engineers were able to increase the range to 19 centimeters, the reliability of the Bluetooth connection from the phone was diminished, Jaffe says. And when the Bluetooth sensitivity was corrected, the NFMI range went back down to 16 centimeters.

Khanna says part of Doppler’s secret sauce is an electrical architecture that manages the interworking of the components such that the performance of both is maximized. “Now there is next to no de-sensing,” Khanna said.

Jaffe and Khanna are hesitant to divulge the details of how they got there. “There’s a certain amount of black magic that goes into making it all work together,” Kraft says.

Black Magic At Scale

Making the product work well in the lab is one thing, but replicating such a delicate recipe in millions of units coming off the manufacturing line is very hard. This seems to be the root cause of Doppler’s delay, and it is likely the cause of Apple’s AirPods delay, too.

“If we were only going to make 50 units this would be no problem,” Kraft says, but Doppler hopes that it will need to make millions of them.

Doppler must rely on its Chinese manufacturer partner to hit a better-than-90% yield, meaning that less than 10% of the products coming off the line can fail any of the 60 or so quality-assurance tests performed on the production floor. Those quality-assurance tests involve many different aspects of the product, including radio frequency, battery performance, safety, audio quality, and other factors.

Kraft says that 90% yield number is needed to preserve profit margins; but the main reason for targeting that success rate is so that very few, if any, consumers receive a product that doesn’t pair well and perform reliably.

Another challenge to mass-producing Here One while ensuring reliability is that the product’s circuit board has to be small enough to fit in an ear and yet must carry around 200 components. The close proximity of the components increases the risk of manufacturing error. If one piece of solder is slightly out of place, the product may not connect to the phone properly, or may not connect at all.

“There are only two fab houses that can build a circuit board of that size and complexity,” Khanna says.

The manufacturing process is at once made simpler and more difficult by the fact that unlike other wireless earphones, Doppler’s left and right buds are identical. While it obviates the need for two distinct production lines, it also creates a scenario where the engineers must fit the full set of components into one earphone design. More stuff crammed in a tiny space, through a more exacting manufacturing process.

Doppler’s Here One buds are somewhat larger than the part of Apple’s AirPods that fit in the ear. Apple decided to reduce the size of the in-ear portion of the AirPod by designing in a post that extends down from the user’s ear. That post provides ample space for antennas, which no doubt improves connectivity and reliability in that product. The Doppler designers felt that those posts make the AirPods less discreet, less aesthetically appealing, and less wearable.

“You have the aesthetics, the battery, and the computer, and if you give up on one you seriously compromise your product,” Kraft said.

So Doppler resisted adding something like the AirPods’ posts to the design of the Here products. “They took the easy way out,” Khanna says, laughing.

Doppler Labs now says it expects that Here One will go into full mass production in January. The company says it will start shipping pre-orders in mid-February and will start selling through mass retail channels in mid-March.