@michaeliv: thanks for your answer.
I wanted to have a short silence-period as a trigger. So there is no button, but if there is silence followed by a small volume of the voice, the messurement should start.
This is another challenge
I have to distinct vioce from environmental noise.
If I would do that in software ( I actally have done this 20 years ago with delphy on a pc) I would use a fft to filter human voice.
I know, that I have to filter a band between 100 and 200 Hz.
So I know, how to do that in Software, but I want to do it in hardware, to have a low-powered wearable device.
At the end, I want to have something, that is mounted on a necklace, that is vibrating, if I speak too fast to loud ....
So my fear is, that an atmega328 is not powefull enough and needs to much power.
I did some experiments with a stm32f04, but I would like to have an analog circuit at most, if it would be possible.