AN4041

Software description

Doc ID 022706 Rev 2

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Software description

The digital signal processing (DSP) consists of the simple flow depicted in the figure below.

Figure 2.

DSP

The PDM signal from the microphone is filtered and decimated in order to obtain a sound

signal at the required frequency and resolution. The loaded firmware implements a filter

pipeline that has been designed as two filtering-decimation stages.

Assuming an input frequency of 3.072 MHz and a desired output frequency of 48 kHz, the

filter stages are configured to implement a decimation factor of 64. The final gain of the

code modulated (PCM) signal.

For further information, please refer to application note AN3998, “PDM audio software