iPhone / iPod touch 4 mic high-pass filter
iPhone / iPod touch 4 mic high-pass filter
- Subject: iPhone / iPod touch 4 mic high-pass filter
- From: Andrew Smith <email@hidden>
- Date: Thu, 30 Dec 2010 21:21:17 +0000 (GMT)
Happy New Years everyone.
We have been developing audio test apps for a long time now, and we are always looking at the frequency response of the microphones in the various iOS devices.
Early devices (original iPhone, for example), had very mild low-frequency rolloff, and with each successive generation the rolloff (actually a high pass filter) got steeper. iPhone 4 had more than 20dB / octave rolloff starting at around 250Hz.
Then iPod touch 4 came out, and it again had a mild rolloff -- less then 10dB at 20Hz. So this we something that worked much better for audio analysis.
But surprise, 4.2.1 comes out, the iPod touch 4 gets upgraded, and sure enough it has a far steeper rolloff. More like 40dB at 20Hz. This is confirmed on my unit, and from several customers in the field.
So, obviously at least part of the high pass filter is enabled in software. I am getting ready to submit a bug report / request to the good folks at Apple, but I'm wondering if anyone else has experienced this, or has by some miracle found a way to control the rolloff from an API.
Best regards,
Andrew Smith
Studio Six Digital
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