Arduino Nano, and AD9850, how can I decrease my sweep time

[samsherpa]

I am currently using Arduino and AD9850 to output frequency from 0 to 200Khz. it takes about 7 to 8 seconds to complete a sweep. How can I decrease the sweeping time?

#include <AD9850SPI.h>
#include <SPI.h>
const int W_CLK_PIN = 13;
const int FQ_UD_PIN = 8;
const int RESET_PIN = 9;
int phase = 0;
void setup() {
  DDS.begin(W_CLK_PIN, FQ_UD_PIN, RESET_PIN);
  DDS.calibrate(124999500);
}
void loop() {
  sweep();
  DDS.down();
  delayMicroseconds(200);
  DDS.up();
}
void sweep() {
  for (unsigned long freq = 1; freq <= 200000; freq++) {
    DDS.setfreq(freq, phase);
  }
}

[CrossRoads]

Decrease this number:
delayMicroseconds(200);

Increase by more than 1 here:
for (unsigned long freq = 1; freq <= 200000; freq++) {

Instead of freq++, use freq = freq + 2, or 3 or 10 or whatever

[Erik_Baas]

Do you really need a linear scale, with all 199998 values between 1 and 200000? If you change the datatype of freq to a double, you could replace freq++ with (for example) freq*=1.1 to create a logarithmic scale. That would make it a lot faster, and also make more sense (IMHO). This will of course not end at exactly 200,000Hz!

PS.: Or use steps of 1.05946309436 (= twelfth root of two), which is a semitone. That will give 12 steps per octave (= ratio 1:2).

[samsherpa]

I cannot use logarithm scale as it will miss frequency in-between.
"Use a step of 1.05946309436" Can you explain more on what this is? Could you give an example.