In part one of this blog series, the characteristics, strengths, and limitations of MEMS microphones were discussed. These are excellent microphones to use in devices that are “forgotten” in cars on hot summer’s days because electrons can be pumped back onto the microphone diaphragm when needed. However, issues such as dynamic range, frequency response, and “factory settings” such as directionality and compression, may create a situation where two Smartphones may be quite different despite being manufactured by the same company.
Another source of error, other than the microphone and its associated technology, is the latency of a device.
Latency is well-studied and the hearing aid industry is no exception. Depending on what you are using the Smartphone (or hearing aid) for, longer latencies can be fine. This is especially the case for listening to recorded music or other recorded information signals such as a low battery warning. However, for live speech and music, a slight delay can be problematical.
Values such as 40 msec have been thrown around as the maximum delay in a hearing aid circuit, before some of the deleterious effects begin to show their ugly head, but some Smartphones can have delays that are much longer. And if you are using your Smartphone in conjunction with other external Bluetooth, or otherwise, enabled devices, these latencies can add up. Even a relatively passive mixing board in a recording studio can add another 5 msec or more in delay.
Typically, it is not one culprit, but the entire stream of devices and technologies that taken together, create a significant delay. Wireless technology can add to the latency as can some algorithms that may be unique to certain apps.
In short, while the hearing aid industry has been very careful to ensure that their hearing aids have a latency that is as short as possible, the issue is that once the hearing aid is connected, especially wirelessly connected, an entire new set of delays can be introduced into the listening environment.
The listing below includes example of latencies that are characteristic of a range of Smartphone devices. This was taken from the Sennheisser website.
Latency 60-70 ms:
• iPod (iOS 8.3-10.0.0)
• iPhone (iOS 8.3-10.1.1)
• Nexus 5 (Android 6.0.0)
• Nexus 5X (Android 6.0.0-7.1.1)
• Samsung Galaxy Nexus (Android 4.3)
• LG G4S H735 (Android 5.1.1)
Latency 70-80 ms:
• Asus Zenfone2 Laser Z00ED (Android 5.0.2)
• PhicommEnergy L (Android 5.0.2)
• Moto G3 (Android 6.0)
• Moto E2 (Android 5.0.2)
• Sony Experia (Android 5.1.1)
Latency > 100 ms:
• Samsung S3 Mini (Android 4.2.2)
• Asus Nexus 7 Tab (Android 5.1)
• Doro Liberto820 (Android 4.4.2)
• Samsung Galaxy J5 (Android 5.1.1)
• Samsung Galaxy Tab 3 lite (Android 4.4.4)
• ZTE Blade L3 (Android 5.0.2)
• Asus Zenfone2 Z00AD (Android 5.0)
• Samsung S4 (Android 4.3)
NOTE: I RECEIVED SOME CORRESPONDENCE FROM RICHARD EINHORN ABOUT THIS AND APPARENTLY I DIDN’T READ THE PREFACE FOR THE ABOVE INFORMATION AS WELL AS I SHOULD HAVE. THESE NUMBERS ARE FOR THE LATENCIES GOING IN BOTH DIRECTIONS THROUGH THE SENHEISSER DEVICE. LATENCIES CAN BE AFFECTED BY MANY THINGS AND THOSE THAT ARE RELATED ONLY TO THE SMARTPHONE WOULD BE LESS THAN THESE NUMBERS. THANK YOU RICHARD FOR POINTING THIS OUT!
Latency is yet another issue that hearing aid wearers and we, as hearing health care professionals, need to be aware of. The addition of “just one more” external device, especially if it is connected wirelessly, can be the proverbial straw that breaks the camel’s back.