How to build a code of time-shifting function generator?

I'm going to make a cymatic device with Arduino Due which makes time-shiftnig patterns.

So I made a source code from the copy of this,

and a cord I made is this.

  Simple Waveform generator with Arduino Due

  * connect two push buttons to the digital pins 2 and 3 
    with a 10 kilohm pulldown resistor to choose the waveform
    to send to the DAC0 and DAC1 channels
  * connect a 10 kilohm potentiometer to A0 to control the 
    signal frequency


#include "Waveforms.h"

#define oneHzSample 1000000/maxSamplesNum  // sample for the 1Hz signal expressed in microseconds 

volatile int wave1 = 0;

int i = 0;
int sample;

void setup() {
  analogWriteResolution(12);  // set the analog output resolution to 12 bit (4096 levels)


void loop() {
  // Read the the potentiometer and map the value  between the maximum and the minimum sample available
  // 1 Hz is the minimum freq for the complete wave
  // 170 Hz is the maximum freq for the complete wave. Measured considering the loop and the analogRead() time
  sample = map(55, 0, 4095, 0, oneHzSample);   
  sample = constrain(sample, 0, oneHzSample);

  analogWrite(DAC1, waveformsTable[wave1][i]);  // write the selected waveform on DAC1

  if(i == maxSamplesNum)  // Reset the counter to repeat the wave
    i = 0;

  delayMicroseconds(sample);  // Hold the sample value for the sample time

// function hooked to the interrupt on digital pin 3
void wave1Select() {
  if(wave1 == 4)
    wave1 = 0;
#ifndef _Waveforms_h_
#define _Waveforms_h_

#define maxWaveform 4
#define maxSamplesNum 120

static int waveformsTable[maxWaveform][maxSamplesNum] = {
  // Sin wave
    0x7ff, 0x86a, 0x8d5, 0x93f, 0x9a9, 0xa11, 0xa78, 0xadd, 0xb40, 0xba1,
    0xbff, 0xc5a, 0xcb2, 0xd08, 0xd59, 0xda7, 0xdf1, 0xe36, 0xe77, 0xeb4,
    0xeec, 0xf1f, 0xf4d, 0xf77, 0xf9a, 0xfb9, 0xfd2, 0xfe5, 0xff3, 0xffc,
    0xfff, 0xffc, 0xff3, 0xfe5, 0xfd2, 0xfb9, 0xf9a, 0xf77, 0xf4d, 0xf1f,
    0xeec, 0xeb4, 0xe77, 0xe36, 0xdf1, 0xda7, 0xd59, 0xd08, 0xcb2, 0xc5a,
    0xbff, 0xba1, 0xb40, 0xadd, 0xa78, 0xa11, 0x9a9, 0x93f, 0x8d5, 0x86a,
    0x7ff, 0x794, 0x729, 0x6bf, 0x655, 0x5ed, 0x586, 0x521, 0x4be, 0x45d,
    0x3ff, 0x3a4, 0x34c, 0x2f6, 0x2a5, 0x257, 0x20d, 0x1c8, 0x187, 0x14a,
    0x112, 0xdf, 0xb1, 0x87, 0x64, 0x45, 0x2c, 0x19, 0xb, 0x2,
    0x0, 0x2, 0xb, 0x19, 0x2c, 0x45, 0x64, 0x87, 0xb1, 0xdf,
    0x112, 0x14a, 0x187, 0x1c8, 0x20d, 0x257, 0x2a5, 0x2f6, 0x34c, 0x3a4,
    0x3ff, 0x45d, 0x4be, 0x521, 0x586, 0x5ed, 0x655, 0x6bf, 0x729, 0x794


#endif m

I made a circuit like this.


Now, I have a trouble that I have no idea how to generate time-shifting sound. I have known map(55, 0, 4095, 0, oneHzSample) generates 70 Hz sound and map(65, 0, 4095, 0, oneHzSample) generates 60 Hz sound.

I want to generate time-shifting sound between these area.

the code might need a for loop structure, but I don't know how to build a correct code.