Hi All Jucers… I need a way to cast a IIRCoefficent to an array of float coefficients so I can use them for designing a filter graph. Is it possible?

# How to cast from IIRCoefficents to array of float

Did you take a look at the class documentation? From there it’s easy to find it out. If you didn’t, you should get used to take a look there first

Now if you’re talking about the old `IIRCoefficients`

class, you’ll find out here https://docs.juce.com/master/classIIRCoefficients.html that it has a public attribute `coefficients[5]`

. So accessing the array is as simple as `myIIRCoefficients.coefficients`

.

If you are talking about the new `dsp::IIRCoefficients`

class, you’ll find out here https://docs.juce.com/master/structdsp_1_1IIR_1_1Coefficients.html that it has the member function `getRawCoefficients()`

returning a pointer to the raw coefficient array. In this case, accessing the array look like `myIIRCoefficients.getRawCoefficients()`

**arstudio**#3

ok thanks! Now I have access to the coefficents:

I have this code:

```
dsp::IIR::Coefficients<float>::Ptr newCoefficients;
switch (filterType)
{
case LowPass:
newCoefficients = dsp::IIR::Coefficients<float>::makeLowPass (fs, frequency, Q);
b0 = newCoefficients->getRawCoefficients()[0];
b1 = newCoefficients->getRawCoefficients()[1];
b2 = newCoefficients->getRawCoefficients()[2];
a0 = newCoefficients->getRawCoefficients()[3];
a1 = newCoefficients->getRawCoefficients()[4];
a2 = newCoefficients->getRawCoefficients()[5];
break;
...
```

And I Pass to this function in paint() of my filterGraph component

```
tracePath.clear();
if (traceType == Magnitude)
{
float scaleFactor = (((height / 2) - (height - 5) / (numHorizontalLines + 1) - 2.5f) / maxdB);
float traceMagnitude = (float) (filterVector [0].getResponse (lowFreq).magnitudeValue);
for (int i = 1; i < numFilters; i++)
{
traceMagnitude *= (float) (filterVector [i].getResponse (lowFreq).magnitudeValue);
}
traceMagnitude = 20 * log10 (traceMagnitude);
tracePath.startNewSubPath (2.5f, (height / 2) - (traceMagnitude * scaleFactor));
for (float xPos = 3.5; xPos < (width - 2.5); xPos += 1)
{
float freq = xToFreq (xPos);
traceMagnitude = (float) (filterVector [0].getResponse (freq).magnitudeValue);
for (int i = 1; i < numFilters; i++)
{
traceMagnitude *= (float) (filterVector [i].getResponse (freq).magnitudeValue);
}
traceMagnitude = 20 * log10 (traceMagnitude);
tracePath.lineTo (xPos, (height / 2) - (traceMagnitude * scaleFactor));
}
}
if (traceType == Phase)
{
float scaleFactor = ((height / 2) - (height - 5) / (numHorizontalLines + 1) - 2.5f) / (float_Pi * maxPhas);
float traceMagnitude = (float) (filterVector [0].getResponse (lowFreq).phaseValue);
for (int i = 1; i < numFilters; i++)
{
traceMagnitude += (float) (filterVector [i].getResponse (lowFreq).phaseValue);
}
float prevPhase = traceMagnitude;
float unwrapSummand = 0;
tracePath.startNewSubPath (2.5f, (height / 2) - (traceMagnitude * scaleFactor));
for (float xPos = 3.5; xPos < (width - 2.5); xPos += 1)
{
float freq = xToFreq (xPos);
traceMagnitude = (float) (filterVector [0].getResponse (freq).phaseValue);
for (int i = 1; i < numFilters; i++)
{
traceMagnitude += (float) (filterVector [i].getResponse (freq).phaseValue);
}
if (fabs (traceMagnitude - prevPhase) > 5)
{
unwrapSummand += float_Pi * 2;
}
prevPhase = traceMagnitude;
tracePath.lineTo (xPos, (height / 2) - ((traceMagnitude + unwrapSummand) * scaleFactor));
}
}
g.setColour (traceColour);
g.strokePath (tracePath, PathStrokeType (1.0f));
```

And I get this error;

**arstudio**#4

the old working code was:

```
switch (filterType)
{
case LowPass:
b0 = (1 - cos(w0)) / 2;
b1 = 1 - cos(w0);
b2 = (1 - cos(w0)) / 2;
a0 = 1 + alpha;
a1 = -2 * cos(w0);
a2 = 1 - alpha;
break;
...
```

And with that code the graph is plotted.With the other, the debugger say to me that the traceMagnitude is NaN…

**daniel**#5

In the line before the error you write:

but the magnitude is likely to be 0 from time to time… so together with log10 it should ring a bell…

**daniel**#7

The logarithm of 0 is undefined, since the equation `y = 10 ^ x`

has no solution for y == 0. The number you are getting for log10 (0) is NaN (“not a number”). So you should check if traceMagnitude > 0 before trying to compute the log of that.

Or even better, make use of the Decibels::gainToDecibels() function.

**daniel**#10

I haven’t read your code, but you probably have to check your maths and in which range the numbers are:

gain = 0 => dB = -infinity (defaults to -80.0, can be specified)

gain = 0.5 => dB = - 6dB

gain = 1 => dB = 0

so you can simply map to your rect:

```
auto y = jmap (Decibels::gainToDecibels (magnitude, -80.8f), -80.0f, 0.0f, rect.getBottom(), rect.getY());
```

BTW. I think this thread will be interesting for you: