title: AUGraph setup on iOS
body: <p>I am designing an AUGraph for an iOS application and would appreciate help on the following things.</p>
  
  <p>If I want to play a number of audio files at once, does each file need an audio unit? </p>
  
  <p>From the Core-Audio docs</p>
  
  <blockquote>
    <p>Linear PCM and IMA/ADPCM (IMA4) audio You can play multiple linear PCM or IMA4 format sounds simultaneously in iOS without incurring CPU resource problems.</p>
    
    <p>AAC, MP3, and Apple Lossless (ALAC) audio Playback for AAC, MP3, and Apple Lossless (ALAC) sounds uses efficient hardware-based decoding on iPhone and iPod touch. You can play only one such sound at a time.</p>
  </blockquote>
  
  <p>So multiple AAC or MP3 files cannot be played at the same time. What is the optimal LPCM format to play multiple sounds at once?</p>
  
  <p>Does this apply to Audio-Units too, as this in under the AudioQueue documentation.</p>
  
  <p>Can an audio unit in an AUGraph be inactive? If an AUGraph looks like this</p>
  
  <p>Speaker/output &lt; recorder unit &lt; mixer unit &lt; number of audio file playing units</p>
  
  <p>what happens if the recorder is not active, would it still pull, but just not write the buffers to a file?</p>