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STM32F4 Microphone Data logging to SD card

Question asked by Anna on May 18, 2016
Latest reply on May 21, 2016 by markt
Hi,
My system is microphone - stm32f401 nucleo board - SD card
I am using ST extension board for mems mic and software STM32CubeExpansion_MEMSMIC1_V1.2.0.
This open source soft is acquires the mic and streaming it to USB ( that recognized by the computer as microphone) every 1msec. every mSec a buffer of 16 samples is transferred to usb. I added to this code SDIO with FatFs +DMA interface. 
every 1 mSec when the streaming buffer is full I am buffering it in double buffer system to bigger buffer of 50 mSec and then writing it to SDcard.
The problems I have: 
1. I am getting a noise like " tuk tuk tuk tuk tuk " in a some frequency (after some measures like 500Hz) . If I am turning off (comment the function)  the "saving data" the noise disappear. 
2. When I am importing to Audacity the binary file of the recordings, the tempo is a little faster then the original sound. (Sampling freq 16000Hz) 


Maybe somebody have an idea?


Thanks

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