A bitstream converter for converting a 1-bit pulse density modulated (PDM) bitstream signal into an analog audio signal, the bitstream converter comprising: a processor configured to process the 1-bit PDM bitstream signal using a return to zero clock having a frequency higher than a sampling frequency of the 1-bit PDM bitstream signal to output a corresponding 1-bit return to zero signal, wherein the processor is configured to process the 1-bit PDM signal to ensure a portion of each bit of the 1-bit PDM bitstream signal is zero for a duration which is based on the frequency of the return to zero clock; and signal processing means configured to extract the analog audio signal from the 1-bit return to zero signal by filtering the 1-bit return to zero signal.