AN3998 Datasheet, PDF (4/10 Pages) STMicroelectronics – PDM audio software decoding on STM32 microcontrollers

PDM signal introduction
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PDM signal introduction
AN3998
Pulse density modulation, or PDM, is a form of modulation used to represent an analog
signal in the digital domain.
In a PDM signal, specific amplitude values are not encoded into pulses as they would be in
PCM. Instead it is the relative density of the pulses that corresponds to the analog signal's
amplitude.
To get the framed data from the PDM bit stream, decimation filters are usually used. The
first stage of decimation is used to reduce the sampling frequency, followed by a high pass
filter to remove the signal DC offset.
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Doc ID 022391 Rev 1