PDM2PCM Library will not link.

[mbmail4]

Hi.

I'm working on a STM32F4-Discovery board, and I'm having trouble linking the PDM2PCM Library into my project.

I have run the example project located in the STM32F4-Discovery folder called "Audio_playback_and_record" and it works fine.

I have copied the settings from this project into my new CUBE project, but when I run the compiler I get the following message

arm-none-eabi/bin/ld.exe: cannot find -l:libPDMFilter_CM4_GCC_wc32.a.

below is an image of my settings, can anyone help me solve this issue?

[nlbutts]

I've been fighting with the SAI sub-system and the PDM2PCM library as well. I can offer some insights on the PDM2PCM library, but I am still having high frequency noise issues.

As I understand it, it is expecting data to be in a byte packet format. This means on a one microphone system you have something like this:

| 8-bits of PDM data | 8-bits of PDM data | ..... | 8-bits of PDM data |

When you call PDM_Filter, you pass in this buffer of data as well as the PCM output buffer. You need to set your decimation factor and your output_samples_number:

PDM1_filter_config.output_samples_number = 1024;

In my case I have 1.536 MHz PDM clock and am decimating by 64. I am using a 8192 byte buffer to hold the PCM data (8192 * 8 bits = 65536 PDM bits)

65536 PDM bits / 64 (decimation) = 1024 PCM samples (16-bit samples).

In my case I'm using two microphones. So the PDM data is packed liks this:

| 8-bits left mic | 8-bits right mic | | 8-bits left mic | 8-bits right mic | ....

Then when you call PDM_Filter, you get:

|16-bit PCM left mic | 16-bit PCM right mic | .....

My problem is I get high frequency noise. It seems like the filter isn't actually filtering. It seems more like it is decimating in time without the low pass filter.

  

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The post is from over a year ago, poster has likely moved on..