Question

Hi it’d like to know if it’s at all possible create a “parametric” equalizer in flash.
Not just the usual graphic effects but a tool to modify the output of the sound that pass trough the application. Any reference, tips idea welcomed.
Thanks

Answer 1

It’s not going to be terribly easy… but here might be a way:

var parameters:Array = [1,1,1,1,0.5]
var sound:Sound = new Sound();
sound.addEventListener(SampleDataEvent.SAMPLE_DATA, filter); 
sound.load(soundURLRequest);
sound.play();

private function filter(event:SampleDataEvent):void
{
    var freqDomain:Array = FFT(event.data, parameters.length); // You will need to find a FFT(Fast Fourier Transform) function to generate an array. 
    for(var i:int = 0; i < freqDomain.length; i++)
    {
        freqDomain[i] = freqDomain[i] * parameters[i]; // This is where your EQ parameters get applied.
    }
    var timeDomain:Array = IFFT(freqDomain, event.data.length); // Inverse FFT

    for(value:Number in timeDomain) 
    {
        event.data.writeFloat(value);
    }
}

Some on the FFT and IFFT functions, FFT usually outputs complex values (real + complex components), which can be converted to magnitude and phase components. What you really need is only the magnitude, which has a formula = (sqrt(real^2 + complex^2)). Humans ears are NOT sensitive to the phase (As opposed to the eyes, which are VERY sensitive to phase), so when you do the inverse FFT, you can insert a random or flat phase with little difference. Note that my approach is very low level in terms of filter implementation.

Here is a Fourier Transform function (not Fast though, it’s just a convolution (O(n^2)) vs FFT O(nlogn)) just for reference (err.. it’s off the top of my head so if might be wrong with the constants):

// Note that this only returns the magnitude, I am discarding the phase.
function FFT(sample:Array, size):Array
{
    var frequencies = new Array(size);
    for(int i = 0; i < sample.size; i++)
    {
        for(int j = 0; i < frequencies.size; j++)
        {
            var real:Number = sample[i] * Math.cos(Math.PI/2 * i * j);
            var complex:Number = sample[i] * Math.sin(Math.PI/2 * i * j);
            frequencies[j] += Math.sqrt(real * real + complex * complex);
        }
    }
    return frequencies;
}