Accelerator Delay Guitar Effect

This code is simple in the idea but the code could be tricky.
The delay time is set to a fixed value and when the TAP footswitch is pressed the delay time is decreased. Once the TAP footswitch is released, the delay time goes to its original value.

The complete code looks like:

// CC-by-www.ElectroSmash.com Accelerator Effect Pedal.
// More info about the project at www.ElectroSmash.com/Time-Manipulator

// Pin Definitions:
#define DELAY1 10
#define DELAY2 9
#define SWA 3
#define SWB 14
#define SWC 2
#define SWD 4
#define LED1_G 1
#define LED1_R 0
#define LED2_G 5
#define LED2_R 6
#define ENC_A 16
#define ENC_B 18
#define ENC_GND 17
#define ENC_PUSH 19
#define BYPASS_DETECT 8
#define TAP_DETECT 15

//VARIABLES
unsigned int ENC_counter = 100;
int ENC_aState;
int ENC_aLastState;
int ENC_aState_selection=0;
int ENC_aLastState_selection=0;

unsigned int ACCELERATOR_counter=0;
int first_time=0;
unsigned long delay_currentMillis,delay_previousMillis = 0;

// the setup function runs once when you press reset or power the board
void setup()
{
//set the pins //init the values
pinMode(DELAY1, OUTPUT); analogWrite(DELAY1, 100);
pinMode(DELAY2, OUTPUT); analogWrite(DELAY2, 100);
pinMode(SWA, OUTPUT); digitalWrite(SWA, LOW);
pinMode(SWB, OUTPUT); digitalWrite(SWB, LOW);
pinMode(SWC, OUTPUT); digitalWrite(SWC, LOW);
pinMode(SWD, OUTPUT); digitalWrite(SWD, LOW);
pinMode(LED1_G, OUTPUT); analogWrite(LED1_G, 0);
pinMode(LED1_R, OUTPUT); analogWrite(LED1_R, 0);
pinMode(LED2_G, OUTPUT); analogWrite(LED2_G, 0);
pinMode(LED2_R, OUTPUT); analogWrite(LED2_R, 0);
pinMode(ENC_A, INPUT_PULLUP);
pinMode(ENC_B, INPUT_PULLUP);
pinMode(ENC_GND, OUTPUT);
pinMode(ENC_PUSH, INPUT_PULLUP);
pinMode(BYPASS_DETECT, INPUT_PULLUP);
pinMode(TAP_DETECT, INPUT_PULLUP);
ENC_aLastState = digitalRead(ENC_A);
void read_encoder(void);
}


void loop() // the loop function runs over and over again forever
{
//detect if the effect is on or off
while((digitalRead(BYPASS_DETECT) == LOW))
{
digitalWrite(LED1_R,LOW);digitalWrite(LED2_R,LOW);digitalWrite(LED1_G,LOW);digitalWrite(LED2_G,LOW);
}

//set the LED (both green)
digitalWrite(LED1_G,HIGH);digitalWrite(LED2_G,HIGH);
//set the audio relays y delay mode
digitalWrite(SWA, LOW);digitalWrite(SWB, HIGH);digitalWrite(SWC, HIGH);digitalWrite(SWD, LOW);

if (first_time==1){ACCELERATOR_counter=120;first_time=0;}// 120 delay by default

//if TAP footswitch is pushed, reduce the delay time (ACCELERATOR_counter)
if ((digitalRead(TAP_DETECT) == LOW) && (ACCELERATOR_counter>=50))
{
digitalWrite(LED1_G,LOW);digitalWrite(LED2_G,LOW);
digitalWrite(LED1_R,HIGH);digitalWrite(LED2_R,HIGH);
//the 6 lines below introduce a delay (60ms), so the delay time (ACCELERATOR_counter) is not reduced too fast.
delay_currentMillis = millis();
if (delay_currentMillis - delay_previousMillis >= 60)
{
delay_previousMillis = delay_currentMillis;
ACCELERATOR_counter--;
}
}

//return to the original position if nothing happens.
else if (ACCELERATOR_counter <= ENC_counter)
{
digitalWrite(LED1_G,LOW);digitalWrite(LED2_G,LOW);
digitalWrite(LED1_R,HIGH);digitalWrite(LED2_R,HIGH);
delay_currentMillis = millis();
if (delay_currentMillis - delay_previousMillis >= 60)
{
delay_previousMillis = delay_currentMillis;
ACCELERATOR_counter++;
}
}

else
{
digitalWrite(LED1_G,HIGH);digitalWrite(LED2_G,HIGH);
digitalWrite(LED1_R,LOW);digitalWrite(LED2_R,LOW);
read_encoder();
}

//update the delay time
analogWrite(DELAY1, ACCELERATOR_counter);
analogWrite(DELAY2, ACCELERATOR_counter);
}

void read_encoder(void)
{
ENC_aState = digitalRead(ENC_A); // Reads the "current" state
if (ENC_aState != ENC_aLastState)
{
if (digitalRead(ENC_B) != ENC_aState)
{if(ENC_counter>50)ENC_counter-=5;}
else
{if(ENC_counter<230)ENC_counter+=5;}
}
ENC_aLastState = ENC_aState; // Updates the prev. state

}