Wave-machine

Amplitude Auto-Adjustment

In the previous article, we learned that because of the ways that sound waves combine, the resulting wave's amplitude can increase. This is inconvenient for us because our sampling code assumes a range of -1 to 1. I worked around this by multiplying the total wave by 0.3, knowing that should cover things, but I want to combine sounds without worrying about it going forward.

Thankfully, this is easy to remedy; all we have to do is take the highest amplitude of the wave and divide the whole thing by that amount. We'll put that in our sampling function:

sampleInt16 :: WaveFunction -> Int -> Double -> [Int16]
sampleInt16 audioFn frequency duration = 
    [floor (v * 32767.5 / maxMagnitude) | v <- samples]
    where 
        samples = sample audioFn frequency duration
        maxMagnitude = maximum (map abs samples)

This places our samples back in bounds. Now we can simplify our Main.hs audio function:

audioFn :: WaveFunction
audioFn = addWaves [
    applyPitch (toneFrequency C 4) sineWave,
    applyPitch (toneFrequency E 4) sineWave,
    applyPitch (toneFrequency G 4) sineWave ]

Here's the output we get when running wave-machine:

To see the code for this article, check out the article-4 branch.

Next, I'm going to going to add sequencing to my experiment code.