2024 Oticon Summer Camp sound excursion
By Jeppe H. Christensen, Principle Scientist
2024-08-23
Sound excursion to Helsingør
You have measured the sound in Helsingør (and possibly at Demant Kongebakken). Hearing aids are equipped with two microphones that continuously sense ambient sound. This is primarily used for hearing-aid signal processing to enable optimal noise reduction, beamforming, and other processing features. However, we can also log the sensed sound to research the typical sound environments that hearing-aid users are exposed to, and how feelings, behavior, stress, and other factors differ between these environments. Note that the logged sound cannot be used to re-construct what has been said!
Sound pressure level (SPL) in Decibels
The sound you are exposed to changes constantly depending on your activity and location. Therefore, it is interesting to inspect a time series of the sound during your trip to Helsingør. This can help you better evaluate if some places had better sound quality than others, and if this corresponded with your own experiences and recollections.
The intensity of the sound is typically measured in sound pressure level (SPL). Below you see the time series of the SPL during your Helsingør trip and Friday morning/noon at Demant headquarters together with the labels of listening activity you selected.
Teams Helix and Concha did a great job making hearing reports! Not surprisingly, the sound was much louder in Helsingør than at the headquarters. However, even at the headquarters, which is typically characterized by office-like sounds, the SPL increased above 80 dB at certain times—perhaps during lunch?
Instead of inspecting single time series, we can also average them across all teams. This way, patterns will reveal common exposure that you all had - perhaps because you were doing group activities or the like. Below you can see the SPL average across data from each team. The fluctuating SPL during your stay in the headquarters reflect a more varying sound experience, while the consitently high SPL in Helsingør might not be that surprising since there is lots of traffic.
Clearness of the sound (signal-to-noise ratio, SNR) in Decibels
Another dimension of the sound you are exposed to is its clearness, or the ratio between what you want to hear (e.g., speech) and disturbing background noise. This is typically measured as the signal-to-noise ratio (SNR), which estimates the difference in decibels (dB) between the target signal and noise. However, in real life, target signals are rarely well-defined—speech from one person can be both a target or noise depending on the listener’s intention. Thus, representing sound clearness using SNR is only a crude estimation of real-world perception.
As hearing aids optimize for speech reception, their estimation of SNR is typically based on the difference between ambient sound that is modulated in frequency and amplitude similar to speech, and unmodulated background noise. This means that the hearing aid will estimate high SNRs if there is a clear speech signal present, but it could also be music or a similar signal that contains modulation similar to speech.
Below, you can see time series of the sound clearness (SNR) you experienced on your trip.
Again, the average time series (shown below) better reflect how your days were different - i.e., in Helsingør the SNR was best around 17.30 and again around 19, while at headquarters, it was more consistent.
