Audio mixer Setfloat() method problem in coroutine

I have a problem, when working with this method (AudioMixer.SetFloat()) in a coroutine. Check out this code.

It is increasing exposed audio mixer parameter linearly every 1.5 second. But the code does not work, especially aud.SetFloat(current_pitch);. When I set pitch parameter using this line of code in coroutine it does nothing.

Result of this expression (MIN_PITCH + LevelManager.instance.Current_extra_pitch) / 100.0f; is at the beginning 0.72. Value 0.72 is logged into the console, too. But pitch parameter in audio mixer is not set.

Please help me out, cause I really do not know what is the problem. ;)

 [SerializeField] private AudioMixer aud;
     
           private IEnumerator soundtrack_speed_increasing(){
     
                 float step;
                 float current_pitch;
                 float next_pitch;
         
                 step = 2 / (2 / .035f);
         
                 current_pitch = (MIN_PITCH + LevelManager.instance.Current_extra_pitch) / 100.0f;
                      
                 Debug.Log(current_pitch);
 
                 aud.SetFloat("Pitch", current_pitch);
         
                 while(true){
         
                     yield return new WaitForSeconds(1.5f);
         
                     next_pitch = (MIN_PITCH + LevelManager.instance.Current_extra_pitch) / 100.0f;
 
                     while(current_pitch < next_pitch){
         
                         yield return new WaitForSeconds(.035f);;
         
                         current_pitch += step;
         
                         aud.SetFloat("Pitch", current_pitch);
         
                     }
         
                 }
         
             }