Suggested settings for PDM filter at 8KHz sampling

[solomonviveros]

Posted on July 29, 2013 at 23:52

What limitations are there within the PDM filter library?

I'd like to be able to record with FS at 8KHz...the original project files show 32KHz spi configuration but FS at 16KHz and the low cutoff at 8KHz; if I want to reduce sampling, how best should I scale the filter coefficients?

example:

AudioFreq = 8000

Filter.Fs = 4000

Filter.LP_HZ = 2000

Filter.HP_HZ = 10

or should it be like the following?

AudioFreq = 16000

Filter.Fs = 8000

Filter.LP_HZ = 4000

Filter.HP_HZ = 10

#stm32f4-discovery-pdm-filter

[peter239955_st]

Posted on October 28, 2013 at 10:34

I have similar questions but seems this is not very active forum to get response. I'm using sample ''Audio playback and recording using the STM32F4DISCOVERY''. Works fine. But for my project I need to sample input audio with higher sampling rate (44.1 kHz). What changes are required to achieve that? Probably I2S clock. But what value must be used? In this sample we are having so many different frequencies (8000, 16000, 32000) and there is no clear indication what is what. I don't understand what is this Fs frequency in PDM_Filter_Init. Is there any better explanation of all this except in AN3998? The suplied sample from ST should really be much better to show all parameters what they mean. 

Thanks in response.