If you're canvas has say 2000 pixels on the x-axis and you're trying to plot one second of 44.1kHz audio, you'll end up with more than 20 samples per pixel. You can then either reduce the number of samples or draw multiple lines within that pixel. Both approaches can result in aliasing. OP's approach seems to just draw lines between every sample, so using the second option. If you change the "Scale" in the example, you can clearly see how peaks appear/disappear due to aliasing (especially between 200 - 400 frames / px).
