title: WebAudio: Steep lowpass?
body: <p>I made a HTML5 game that uses ADPCM samples and music.</p>
  
  <p>The music itself is at 11025Hz mono and I made a simple nearest-Neighbour-Resampler to get 22050Hz plus a fake stereo algorithm.</p>
  
  <p>The samples are pre-upsampled during loading to reduce CPU load during runtime (no realtime-resampling needed).</p>
  
  <p>So I achieved that real retro-sound like in the late 90's.</p>
  
  <p>Works fine so far.</p>
  
  <p>But the "real" resampler of WebAudio that matches the 22050Hz to the internal sample rate seems to be not even better on some browsers :-D.</p>
  
  <p>How can I chop off everything above 11025Hz (Nyquist frequency of 22050Hz)? Ideal would be: 0-11025Hz untouched but 11026Hz-max filtered out.</p>
  
  <p>The low pass filter provided by the WebAudio api isn't steep enough and produces resonances at the filter frequency.</p>
  
  <p>I don't want to allow the "crappy" frequencies going so high. The "crappy" resampling should stop at 11025Hz. I think, it isn't good to tweeter speakers and even the players hearing when the strong bass frequencies mirror at high frequency range.</p>
  
  <p>Don't want MP3&amp;Co here. ADPCM->MP3 needs more bitrate than real ADPCM (The desired artifacts of that are hard to encode without audible loss) :-).</p>
  
  <p>I read about FIR and IIR filters but I didn't understand them because it is too mathematic to me. </p>
  
  <p>I think, this is, what I need.</p>
  
  <p>I need something that can be transformed to code without having a academic degree :-D.</p>