The coordinates of visualisation of the frequencies of a signal?

[caoleiwe]

Hi everyone,
In tutorial:" Visualise the frequencies of a signal in real time", it visualises the frequencies of a signal in real time. However, it does not have the coordinates of frequency (x-axis) and amplitude (y-axis) domains. How could draw their coordinates?

Best regard!

[caoleiwe]

Anyone could help me?

[daniel]

There are plenty threads on the forum, the magnifier icon lets you search for FFT to find e.g. this thread:

FFT Amplitude

It has been a while since I used an FFT and instead of porting some old C# sharp code I’m trying out juce’s. Here’s what I understand: The frequency of bin[x] = Fs / nth Record. In the past I have multiplied the real and imageinary parts but using fft::performFrequencyOnlyForwardTransform only modifies the array going in. Is the data in that array a linear amplitude? My other question is if say the FFT is (10th Order) 512 bins do I need to supply 512 or 1024 samples? (my guess is that if its…

TL;DR: the amplitude is linear from 0 to fft.getSize(), so you might want to normalise by:

y = jmap (bin [i], 0.0f, float (fft.getSize()), float (bounds.getBottom()), float (bounds.getY()));

Now the frequency is linear as well (which is annoying, since you get plenty information about higher frequencies, but not much for lower ones).

These are the two mapping functions I use:

inline float indexToX (float index, float minFreq) const
{
    const auto freq = (sampleRate * index) / fft.getSize();
    return (freq > 0.01f) ? std::log (freq / minFreq) / std::log (2.0f) : 0.0f;
}

inline float binToY (float bin, const Rectangle<float> bounds) const
{
    const float infinity = -80.0f;
    return jmap (Decibels::gainToDecibels (bin, infinity),
                 infinity, 0.0f, bounds.getBottom(), bounds.getY());
}

Hope that helps

[caoleiwe]

Thank you!!!

[gustav-scholda]

btw log(x) / log(2) = log2(x)

[daniel]

Thanks, I missed that this existed!