controlling pc fan digital leds

Using Arduino LEDs and Multiplexing
3

Here it is:

#include <FastLED.h>


#define NUM_LEDS 36
#define NUM_FANS 3
#define OFFSET 12
#define MAX_VAL_METER 20
#define DATA_PIN 2
#define CLOCK_PIN 12

// Define the array of leds
CRGB leds[NUM_LEDS];
int normal[13]={10,11,0,1,2,3,4,5,6,7,8,9,10};
int reverse[13]={10,9,8,7,6,5,4,3,2,1,0,11,10};
int values[20]={8,3,1,2,17,1,4,7,9,5,7,13,1,4,12,16,14,11,2,14};


void setup() { 
       Serial.begin(9600);
       FastLED.addLeds<WS2812B, DATA_PIN, GRB>(leds, NUM_LEDS);
}
void audioMeter(int currentFan,int counter,int maxVal)
 {  
    int l1=0;
    int l2=0;
    int curCount=0;   
    int offset = 12*currentFan;    
    while(counter<maxVal){    
        l1=normal[curCount];  
        l2=reverse[curCount];    
       
        l1=reverse[curCount];
        l2=normal[curCount];
        
        leds[l1+offset]=CRGB::Blue;
        leds[l2+offset]=CRGB::Blue;
       
        FastLED.show();
       
        curCount++;
        counter++;
       
        if(curCount==6 && counter<maxVal)
        {
          
          audioMeter(currentFan+1,counter,maxVal);
        }
    }  
 }
  
 
void loop() 
{ 
 
  {
   FastLED.clear ();   
   audioMeter(0,0,values[i]);
   delay(10);
  }
}

2 arrays for storing the clockwise and the anticlockwise led disposition, 1 array for emulating the sound value.
Now, I'm asking:

is there a better way to turn all the leds up to the desired step/value?

since turning all of the leds off before preparing them for the next value leads to unnecessaries blinks, is there a good way to go back/forward to a lower/higher value?

Thanks in advance!