Audio bandwidth on iMX6

I found, that the audio bandwidth is about 10kHz at 3dB attenuation on the Apalis iMX6D module. I use the winmm api with 48000kHz samplerate. This bandwidth limit only occurs on the input part, the output part works well. What could be the reason? Or can this be set somewhere?

Sampling rates are defined by SGTL5000 audio codec settings. You can try to adjust sampling rate by SGTL5000 direct register access as described here.
Details about SGTL5000 internals available here.

Thank you your answer. I tried it, but the problem is not in the codec. I think the Windows use the Asynchronous Sample Rate Converter module of the iMX6 and it has low pass filter. I think it, because I measured the SGTL5000 I2S_LRCLK signal, and this independent of the winmm api setting, it’s always 44,1kHz. The sampling frequency is ok what i get from winmm api, it’s equal to the winmm value (in my case 48kHz). If i change the sample rate to 48kHz in the codec the output changes to 52,2kHz. I did another test, i passed the audio signal inside the codec (line_in-> adc-> dac-> hp_out) and the frequency transmission was fine. So something happens after the codec. Could you check the Asynchronous Sample Rate Converter settings if it is used?