How do I realize I'm starting to hear less?

Generally, the first sounds to not be heard are ‘high-pitched tones’ such as consonant sounds like C-S-F-Z. At the same time, low frequency noises (appliances, traffic) seem to becoming louder and more annoying. Hearing amid noise begins to be a problem. If a conversation is going on in traffic or if several people are talking at once, trying to understand is very difficult.