Observing the breath vs Pranayama
Calm down the mind - breath is indicator of mind state. 

https://plumvillage.org/sutra/discourse-on-the-full-awareness-of-breathing/


  
  ‘Breathing in a long breath, I know I am breathing in a long breath. Breathing out a long breath, I know I am breathing out a long breath.
  ‘Breathing in a short breath, I know I am breathing in a short breath. Breathing out a short breath, I know I am breathing out a short breath.
  ‘Breathing in, I am aware of my whole body. Breathing out, I am aware of my whole body.’ He or she practices like this.
  ‘Breathing in, I calm my whole body. Breathing out, I calm my whole body.’ He or she practices like this.
  ‘Breathing in, I feel joyful. Breathing out, I feel joyful.’ He or she practices like this.
  ‘Breathing in, I feel happy. Breathing out, I feel happy.’ He or she practices like this.
  ‘Breathing in, I am aware of my mental formations. Breathing out, I am aware of my mental formations.’ He or she practices like this.
  ‘Breathing in, I calm my mental formations. Breathing out, I calm my mental formations.’ He or she practices like this.
  ‘Breathing in, I am aware of my mind. Breathing out, I am aware of my mind.’ He or she practices like this.
  ‘Breathing in, I make my mind happy. Breathing out, I make my mind happy.’ He or she practices like this.
  ‘Breathing in, I concentrate my mind. Breathing out, I concentrate my mind.’ He or she practices like this.
  ‘Breathing in, I liberate my mind. Breathing out, I liberate my mind.’ He or she practices like this.