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A user of my live-looping iOS app reported something bewildering to me recently: He's just replaced his 4th-gen iPod Touch with the new iPod Touch, and suddenly, his bass response when using my app (and most others) with a number of different external analog audio interfaces (including the iRig) has vanished.

Exhibit A, bass present: http://cl.ly/3j261Z0H2v2U
Exhibit B, bass gone: http://cl.ly/1t3z0s0P0208

Most bizarre, though, is this: He's discovered that if he launches JamUp, the guitar effects processor, before launching my app (and all the other apps that exhibit this same issue), the bass returns.

Conversely, if he launches my app, then launches JamUp, JamUp too experiences the no-bass issue.

I've spoken with the JamUp guys and they're just as baffled as I am.

Does anyone have any theories as to why this is happening, and what might be done about it? Anyone else noticing it too?

dandan78
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Michael Tyson
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  • Do we know the cut-off frequency? I postulate that this might be tied up with detection with EQ and audio routing - certainly any audio destined for the internal speaker would be heavily EQ to to remove frequencies the transducers can't reproduce. – marko Jan 06 '13 at 18:44
  • I've just asked the user if he's in a position to be able to determine that - could be useful info. That's an interesting theory, and could help explain why the existence of one app affects another. – Michael Tyson Jan 06 '13 at 22:35
  • Any chance it has to to with the session mode? AVAudioSessionModeMeasurement – Lucas Goossen Sep 11 '15 at 02:09
  • Indeed it does. Measurement mode disables the internal audio processing, which includes a highpass filter. – Michael Tyson Sep 12 '15 at 03:38

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