My father’s in his mid 70s and his hearing isn’t very good in the frequency range that would be useful for finding his vacuum leaks.
I was thinking about setting him up with a directional microphone and a pitch-shifter app to bring environmental sounds down a couple octaves so he can hear them. There are tons of Android/iPhone apps that will pitch-shift in post, but none of the trial/freemium ones seem to work on a realtime monitor stream, especially on an external USB (UAC) microphone. I don’t want to start buying dozens of apps just to try them.
Any app suggestions or other ideas for him?
I’m assuming he’s already got and wearing hearing aids? If so, you might be able to leverage much of what you’re looking built into what he has.
Hearing aids are configured specifically for that user to do the pitch shifting. Your father’s audiologist knows which frequencies your father is able to hear, and has programmed the hearing aid to move audible sound into those specific ranges. So that part is done. However, that likely doesn’t help on its own because hearing aid microphones are located and tuned for human speech etc to assist people in maintaining communication. There’s also limitation on the hardware because they have to be TINY to fit in/around ears and run on low power.
Enter the Buddy Mic! (aka companion mic, aka handy mic)
This is an external microphone with its own power supply and sound processor that attaches wirelessly (bluetooth LE usually) to the exact brand of hearing aid your father is using. Its a tightly integrated solution, so its pretty reliable and easy to use. I got one of these for my mother who had a similar need for augmented hearing at a distance, it works great!
Further, the one for my mother’s hearing aid brand has a 3.5mm jack on it that allows for a wired mic to be plugged into the buddy mic if you need more advanced audio solutions or frequency response handling.
For your father’s use case, he could enable his buddy mic, which would connect wirelessly to his hearing aids, then he could hold the buddy mic in his hands centimeters away from whatever he’s trying to detect sound off of.