All iDevices running iOS 5 have a built-in low cut filter for the built-in microphones and the headphone jack input.
This issue has been solved by Apple since iOS 6.
The reason for the low cut of the pre-iOS 6 devices is – as we believe – that they are designed mainly for recording and processing human speech. This high-pass represents a serious drawback for all kinds of frequency related measurements based on the use of the built-in microphone or the headphone jack. We gave this problem a lot of thoughts and decided to develop a compensation.
Please note: the compensation curves (offered as In-App purchases in the Analyzer and the Spectrograph) compensate for the corresponding device, microphone and (in the case of running iOS 5.x) the heavy low cut filter. In the latter case we are aware that the compensation pushes the noise in the low frequencies, but after much testing done by experienced sound engineers we are very happy with the results! Compensation curves are available for the built-in microphones (on Analyzer included), selected headsets and the i-series mics i436, i456 and i266 from MicW. We offer the frequency responses as In-App Purchases. You can get them by visiting the store in the menu.
The compensation for the measurement microphone i436 from Mic-W includes a setting for the individual sensitivity given in the manual of each i436. In Germany, Switzerland and Austria all products from Mic-W are distributed by Synthax GmbH.
If you are running our Apps on iOS 6 or later, the compensation curves linearize the frequency response of the corresponding microphones and devices.
Frequency responses of the iDevices running iOS 6 (measurement mode activated):
Here are the frequency responses of some external mics available for iDevices attached to the headset input:
The MicW i436 manual provides an individual sensitivity value. We integrated this as a setting in the i436 info page: