1. The tone blows from low to high, and you can't hear it when you blow.

One possible reason is that what you say is beyond the hearing range of human ears, and you simulate the original vibration between muscles while raising the frequency, or the vibration amplitude is quite small, and the sound wave energy that can be excited is not enough for the ears to distinguish.

As for the specific one, we should carefully study the particularity of different people whistling in order to further judge.

Sometimes many people can't hear clearly when talking together ... If different people have different tones at this time, can people hear clearly separately?

People can hear clearly because they can collect the frequency and intensity of sound waves that change periodically to the eardrum for a period of time, and then they are processed by the brain to produce what we call hearing. However, sound waves belong to mechanical waves, and there will be many distortions in the propagation process. There are many reasons, such as noise interference, or through different media (people in the water shout, people on the shore can't hear what he wants to say), and the superimposed influence of fluctuations (people who are far away from the door talk, you will feel that the sound seems to be coming from the door, as if the door is talking). These are all determined by the wave nature of sound waves.

The problem you encounter is caused by the interference of sound waves in the propagation process.

Whether people can hear clearly is not complete because of different tones, because this is not the main reason. It can only be said that people can hear clearly when the sound waves are superimposed, and it is a regular fluctuation. Whether it is formal or not depends on the specific situation.

If you want to know more about it, please go to the library and have a look at the concrete solutions of the chapter on college physics, material waves and mechanical waves, and you will find the answer.