High-quality reconstruction lowpass-filter for digital audio

This low-pass filter can be used as a reconstruction filter at the output of a digital-to-analog converter (DAC) and is particularly suitable for digital audio. Nowadays, digital audio devices e.g. CD-players use digital signal processing to remove unwanted signal components above the Nyquist frequency, e.g. with oversampling or noise-shaping techniques. However, the DAC delivers a signal with radio-frequency components up to the megahertz area. A reconstruction filter must be able to suppress these RF components without impacting the desired signal. The circuit presented here is one of the best solutions for this. R1 and C1 compose a passive low-pass filter, which is able to remove the unwanted RF signal components. Together with the rest of the circuit they form a 3rd order Butterworth-lowpass, which has a maximum flat amplitude frequency response for the desired signal.

Settings

Settings

Frequency response

Frequency response

Circuit and components

Circuit Components

This design has been created using AktivFilter 3.2 software.