For some people, certain hardware devices such as hard drives (HDDs) and some power supplies can emit a high pitch "whine" which can be very annoying to the customer. It can be expected for high-performance enterprise HDDs (10-15K RPM) as those generally live in datacenters or separate server rooms. However, when it comes to consumer products that exist in living rooms or bedrooms, consumers who can hear these tones want products that do not emit high-pitch frequencies. Other examples include: Uninterruptible Power Supplies (UPS'), the power supply for your PC or a power adapter for your media streamer.
Recently I purchased a media streamer and the power supply was emitting a high pitch frequency. Instead of hearsay, I wanted a method to measure and prove the device was emitting what some would consider an "annoying" high-pitch frequency. There are several hardware-based sound analyzers one can purchase; however, I found a better solution that works on an iPhone, SPLnFTT Noise Meter for iPhone ($3.99) . I used an iPhone 5s for testing--it works with iOS 7 and gave me the data I needed to prove to a manufacturer there was an issue. While there are reports of other users experiencing the same problems on their forums and elsewhere, I do realize when a company manufactures 100k+ devices, it is possible to get a lemon. For that reason I've hidden the logo on the manufacturer's AC power adapter.
With any analysis and review, I have tested this to reproduce the issue multiple times and the results are consistent. I am not an audio engineer, nor do I work with professional audio equipment. An iPhone is probably not the best tool if you are looking for high-accuracy audio analysis/results; however, this app was able to provide me the data I was looking for to prove my case.
Here is the AC power adapter I used:
Using SPLnFTT for iPhone, you can clearly see 12,532Hz being emitted from the AC power adapter:
After disconnecting the AC power adapter, it drops to 474Hz:
Curious what 12,000Hz sounds like? If so, make sure your volume is set low before you play the video :
I was not selected to review this sound application, I searched the gamut of sound apps for iOS and this was the best one I found that met my requirements.