## Trippr audio programming: Interpolated noise (part 4)

December 11, 2018 - Jos van Tol

As a little addendum I'll talk a bit about the secret noise I've added to the Trippr tone. It's silently there in the background. It's a version of Brownian noise by interpolating between random points in the signal.

We'll divide our buffer in evenly spaced blocks. We'll use a power of two so it'll fit nicely. In this case 64 (2^{6}), which will fit sixteen times in our buffer of 1024 (2^{10}) samples. These blocks will smoothly step between random points. We'll save all our samples in an array called Noise.

```
uint32_t Smooth = 64;
```

float Random[SamplesToWrite / Smooth];

int16_t Noise[SamplesToWrite];

Now we'll get random values between -1 and 1 to interpolate between. We will have to set the first and last one to 0 so the ends will always meet nicely.

```
Random[0] = 0.0f;
```

Random[SamplesToWrite/Smooth] = 0.0f;

for (uint32_t i = 1; i < SamplesToWrite/Smooth; i++)

{

Random[i] = (float)rand()/(float)RAND_MAX * 2.0f - 1.0f;

}

Now we'll use the **Smoothstep()** function to interpolate between these points. Then multiply these by the 16-bit min/max 32,767.

```
for (uint32_t i = 0; i < SamplesToWrite/Smooth; i++)
```

{

for (uint32_t j = 0; j < Smooth; j++)

{

Noise[i*Smooth + j] = (32767 * Smoothstep(Random[i], Random[i+1], Smooth, j);

}

}

The Smoothstep() function I got from this great site. This is it:

```
float Smoothstep(float A, float B, uint32_t N, uint32_t i)
```

{

float t = i/(float)N;

t = t * t * (3 - 2*t);

return (1.0f -t)*A + t*B;

}