In order to convert the incoming data stream into PCM audio samples, a decimation filter is included in the PDM peripheral.
The filter input is a two-channel PDM serial stream (with left channel on clock high, right channel on clock low). Output consists of two 16-bit PCM samples at a sample rate lower than the PDM clock rate and a ratio defined by the RATIO register.
A digital volume control is implemented within the filter stage of each channel. It can attenuate or amplify the output samples in a range of ±20 dB of the default (reset) setting and is defined by GPDM,default = 0 dB. The gain is controlled by the GAINL and GAINR registers. As shown in #concept_eqb_fw2_yr__section_vqt_d1g_xcc, depending on OSR value, internal compensation is added for fixed predefined OSR values and a programmable one is available for custom OSR values.