> For the complete documentation index, see [llms.txt](https://qudelix.gitbook.io/home/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://qudelix.gitbook.io/home/general/dac-lpf.md).

# DAC LPF

The **DAC LPF (Low-Pass Filter)** setting selects the digital interpolation filter used inside a **Delta-Sigma DAC (Digital-to-Analog Converter)**.

### How It Works

A Delta-Sigma DAC does not directly convert the incoming PCM samples into the final analog waveform.

Before conversion, the PCM signal is internally **oversampled** to a much higher sample rate. During this process, a digital interpolation filter is used to reconstruct the signal between the original PCM samples and suppress unwanted frequency components above the audio band.

The DAC LPF setting changes the characteristics of this interpolation filter.

Depending on the selected filter, the DAC may have different:

* Roll-off characteristics
* Phase response
* Impulse response
* Pre-ringing and post-ringing behavior
* Attenuation near the Nyquist frequency

### Fast Roll-Off vs. Slow Roll-Off

A **Fast Roll-Off** filter attenuates frequencies more aggressively near the Nyquist frequency.

This provides better suppression of out-of-band images, but generally produces a longer impulse response and more ringing around sharp transients.

A **Slow Roll-Off** filter uses a more gradual frequency cutoff.

This can reduce ringing in the time domain, but the frequency response may begin to decrease earlier near the upper end of the audio band.

### Linear Phase vs. Minimum Phase

A **Linear Phase** filter maintains the same phase relationship across frequencies.

Its impulse response is normally symmetrical, which results in both pre-ringing and post-ringing.

A **Minimum Phase** filter removes or greatly reduces pre-ringing by shifting the ringing after the impulse.

However, unlike a linear-phase filter, it introduces frequency-dependent phase shift.

### Does It Change the Sound?

The differences between DAC LPF modes are usually very small.

Most of the differences occur near the upper frequency limit of the audio band and in the impulse response of the DAC.

Depending on the audio content, headphones, listening level, and listener, the difference may be subtle or completely inaudible.

The DAC LPF is not an Equalizer (EQ) and is not intended to make large tonal changes.

### Which Filter Should I Use?

There is no universally best filter.

The default filter is recommended for normal use because it provides a well-balanced combination of frequency response, image suppression, and time-domain behavior.

Other filters are provided for users who want to choose different Delta-Sigma DAC reconstruction characteristics or experiment with their preferred filter response.

Changing the DAC LPF does not change the amplifier power or normal volume range.