man with airpods pro

Apple AirPods Pro® as Hearing Aids — How Effective is Conversation Boost?

Welcome to our Noopl Deep Dive Series

The distinction between medical device hearing aids and consumer audio products has started to blur over the last five years due to the maturation of truly wireless stereo (TWS) earbuds. Apple’s AirPods Pro, for example, now features multiple microphones, motion sensors, active noise cancellation, and high-fidelity output. Moreover, Apple's long-standing commitment to improving the accessibility capabilities of their products has people eagerly anticipating additional improvements for those with hearing loss that began with features first introduced with iOS 14 in September 2020.

In this series of articles from the team at Noopl, we will take a data-based approach to examine the efficacy of AirPods Pro as hearing aids, and the circumstances in which Noopl is of significant additional use to those who struggle with hearing in noise. For the next several weeks, we will share details about Headphone Accommodations, the range of hearing loss that can be “fit” by AirPods Pro, and the respective audiological advantages and drawbacks of TWS earbuds versus Class II medical device hearing aids. Along the way, we’ll also answer your questions, so please comment below!

Our First Assessment: Conversation Boost

Apple’s most recent hearing enhancement feature, Conversation Boost, was announced for iOS 15 and made its appearance in a beta version of firmware for AirPods Pro (version 4A362b) in early August 2021. Conversation Boost takes advantage of the dual microphones built into each AirPod to create a forward-facing directional beam.

AirPods microphones

Figure 1. AirPods teardown showing two MEMS microphones on either side of the force sensor in the stem of the device

 

Conversation Boost is enabled when AirPods Pro are in Transparency Mode and Headphone Accommodations are turned on.

iPhone conversation boostFigure 2. Headphone Accommodations screen showing Conversation Boost switch and Ambient Noise Reduction control

 

When toggling Conversation Boost on and off in a quiet environment, the typical increase in the noise floor associated with two-microphone directional processing was apparent. As expected, enabling Conversation Boost did not furnish a significant advantage when having a one-on-one conversation with a colleague in a relatively quiet office, since directional processing systems are designed for conversations in noisy environments. To informally evaluate Conversation Boost in a noisy environment, an AirPods Pro user conversed with a colleague at a distance of 1 meter while a recording of restaurant noise played behind him through a single loudspeaker, also at a distance of 1 meter. In this case, Conversation Boost enabled a modest improvement that can be characterized as about the same magnitude offered by a well-designed directional system available in modern hearing aids.

Quantitative Assessment

To quantify the magnitude of the benefit from Conversation Boost, we made careful recordings using the setup pictured below.

Noopl lab

Figure 3. Lab with EARS and typical six loudspeaker configuration

 

Measurements were made using the reliable miniDSP EARS (Earphone Audio Response System), which, in turn, was connected to a MacBook Pro via a USB cable for recording. The sound field consisted of an individual subject’s speech playing through a speaker located directly in front of the listener at a distance of 1 meter while independent sample recordings of restaurant noise drove the other five loudspeakers arrayed around the listener at distances of 1.5 to 2 meters. The overall level of the combined speech and noise signal as measured at the listener’s location was 65 dB SPL and the signal-to-noise ratio (SNR) of the speech signal was approximately 2.5 dB, representing a challenging but not uncommon SNR for conversations in a busy restaurant. Importantly, the signals and associated levels were identical across the following measurement conditions:

  • Open EARS
  • AirPods Pro in place (see Figure 4) with
    - Transparency alone 
    - Transparency with Headphone Accommodations (HA)
    - Transparency with HA and Conversation Boost
    - Noopl with Headphone Accommodations

Earphone Audio Response SystemFigure 4. miniDSP EARS (Earphone Audio Response System)

To estimate the signal-to-noise ratio (SNR) for each test condition, we computed the RMS level of two adjacent segments of the waveform, each about 82 milliseconds (ms) in length. For the noise estimate, we used a sample without any speech (i.e., between utterances) just prior to the utterance of the word “Dave” in the recording. Likewise, for the speech estimate, we used a segment of the word “Dave.” To make the comparisons straightforward, we used the same recording segments for each test condition. We also used those segments to plot the fast Fourier transform (FFT) illustrating the frequency-specific changes in SNR across test conditions.

Results

The key test results are summarized in the table and figures below. The table shows the broadband SNR for each condition, and the figures illustrate the frequency-specific changes. For each figure, the FFT of the speech segment is shown in blue and the noise-alone segment is shown in orange. We have included the audio recordings for you to listen and compare for yourself.

 

Condition
SNR (dB)
SNR change (dB)

Open EARS

2.54

Transparency Mode alone

2.81

0.27

Transparency Mode + Headphone Accommodations

2.99

0.45

Transparency Mode + Headphone Accommodations + Conversation Boost

8.26

5.72

Noopl + Headphone Accommodations

16.30

13.76

 

Open EARS

This is the baseline recording from the miniDSP EARS simulating sound entering directly into a person’s ears.

Transparency Mode alone/Transparency Mode + Headphone Accommodations

As expected, there’s not much change in the SNR for the AirPods Pro in Transparency Mode alone. Likewise, there isn’t a significant change in SNR with the addition of Headphone Accommodations. Although this might be a surprise to some readers, the purpose of Headphone Accommodations is to provide a modest compensation for the audibility of speech, particularly at low levels. This goal is accomplished by providing frequency-specific gain, particularly for soft signals. Even if Headphone Accommodations provided more gain for this moderate input level condition, we would not expect a significant change in the SNR because the HA algorithm doesn’t differentially segregate and process speech from noise.

Transparency Mode + Headphone Accommodations + Conversation Boost

With the addition of Conversation Boost, however, we see a significant and meaningful improvement in the SNR of about 5.5 dB, corroborating our impression that Conversation Boost furnishes a hearing benefit approximately equivalent to that of a well-designed directional hearing aid.

It’s also worth mentioning that for people with mild to moderate hearing loss, the benefit of Conversation Boost might be greater than what could be achieved with a directional hearing aid. Because AirPods Pro are tightly acoustically coupled in the ear canal, the SNR advantage provided by directional processing doesn’t have to compete with sound entering directly into the ear canal. In contrast, most hearing aid wearers with mild to moderate hearing loss have a relatively “open” fitting which allows low-frequency signals to flow both in and out of the ear in order to minimize the occlusion effect (the unnatural sound quality of the user’s own voice when their ears are plugged). The directional benefit for hearing aid wearers with open fittings is thus restricted to higher frequencies, where the output of the hearing aid is substantially higher than the direct path sound through the open coupling.

Noopl + Headphone Accommodations

The final test condition shows the magnitude of the SNR improvement when Noopl is combined with Headphone Accommodations. With the announcement of Conversation Boost, we’ve been asked by customers and interested parties whether Apple’s new feature might put us out of business. We hope that the improvement shown here of over 13.5 dB puts that question to rest!

These results do however underscore that Noopl is intended for use in noisy environments. Like the potential loss of benefit in an open fit hearing aid configuration, Noopl will yield a reduced benefit when used with AirPods Pro in Transparency mode. In this case, rather than the direct path of sound through an open hearing aid fitting, it’s the signal through the AirPods Pro microphones that competes with the superior signal coming from Noopl.

It's also important to point out that although many associate Headphone Accommodations solely with the microphone signal of AirPods Pro (Transparency Mode), Apple also supports Headphone Accommodations application to phone calls, and streamed media. In this context, Noopl is a streamed media source.

1 open ears

1 transparency1 transparency+strong headphone accommodations

1 transparency + conv boost + HA1Noopl+HA-1

Summary & Conclusions

Although true wireless stereo (TWS) earbuds have started to blur the line, it should be emphasized that earbuds are NOT hearing aids. Hearing aids in the United States today are Class I or Class II medical devices. And despite legislation passed in 2017, the FDA has not yet provided guidance on the definition of what the new category of over-the-counter hearing aids will be. In the meantime, while confusion exists, reputable consumer electronic companies like Apple and Noopl are providing features that offer many of the same benefits, and in some cases superior benefits, to those found in modern hearing aids.

Conversation Boost, which will be available with the release of iOS 15 in the Fall of 2021, represents a solid new option for hearing a little better in modest background noise conditions for people who either don’t yet need or want traditional hearing aids. Noopl combined with AirPods Pro or Made for iPhone (MFi) hearing aids represents an even better option for hearing in any amount of background noise—from a loud restaurant to a noisy workplace to the din of trains, planes and busses.

In our next installment of this series, we’ll take a closer look at Headphone Accommodations and explore the extent to which TWS earbuds can compete with hearing aids. Stay tuned! We look forward to your comments and questions in the meantime.

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