Digital Subsonic (DC) Filter in dCS Rossini, can it be switched off?

I’m doing some serious critical listening to compare several DACs, including the Rossini (without APEX), which is btw. a great sounding device.

Because I also have the capability to measure with an audio analyzer, I found, that compared to most (all?) other DACs in its price range, the Rossini seems to be incapable to output a DC signal. Since I’m pretty sure it doesn’t do this kind of highpass or subsonic filter in the analog domain (coupling capacitors …), the DAC most likely performs this in the digital domain, which means software.

Since this introduces a phase shift in the sub bass region, there could be audible differences to other DACs simply due to this filter.

So is it possible to switch this potentially sonically harmful filter off, to avoid such troubles ?

What was the reason to implement this on the Rossini and why it isn’t mentioned in product literature ?

Hi Mirko,

First of all, welcome to the community. You’ll find this a friendly forum where we (most of us) owners of dCS equipment genuinely want to help.

Reading your question, I’m wondering whether you are asking about an output signal that is DC, or perhaps something else that is static (such as the frequency)? What is it you’re seeing/not seeing on your analyser?

While I’m no expert in audio design, I’m fairly sure a DC signal in a Hi-Fi chain would not work out well (as in damage the speaker drivers), so I thought I should check before answering.


Dear Jeremy,

you are absolutely right, that this DC test is not very realistic for a normal use, but the insight from it is very valuable. I’m even pretty sure that I have opened a little box of pandora here :innocent:

The measurement is damn simple. I apply a DC offset in digital generator of my AP SYS-2722 and the DAC should present a DC voltage at the analog output (No amp and speakers connected :slightly_smiling_face:). If this doesn’t happen and the voltage stays at ~0V, the DAC has a highpass filter in its digital or analog sections.

In order to protect gear like speakers against very slow signals (down to DC) the so called corner frequency of such filter needs to be lets say in the 0.1…1Hz area and this can produce significant phase shifts up to 100 Hz or so, which could be audible (This is the reason, why such a filter is almost always switchable in amplifiers). One could document that behaviour of the Rossini by a more realistic frequency and phase response measurement (I will probably do), but when the DAC is not able to provide DC in the mentioned synthetic test, we have a clear proof, that a subsonic filter is active.

If this is done in the digital domain (FPGA, DSP), a so called IIR filter (in contrast to the FIR interpolation filters used for oversampling) has to be used, which is widely known for its pathological behavior regarding numerical errors and instabilities in its calculations, which would necessitate additional measures and compromises regarding SQ, like dither etc.

With all these problems related to a digital subsonic filter, the question is, why this is not better solved in the amplfier. All good amplifiers have DC protection and some of them have switchable subsonic filters.

Since no other top DAC brand I know, does that and I never heard, that a DC or subsonic signal from a DAC of another brand ever killed a woofer or triggered the DC protection of an amplifier, the question is, why is it in, why can’t you switch it off and why is this feature not marketed ?

This goes to dCS’ engineering and product management.

Hi Mirko,
Welcome to the forum : )

I am tagging dCS technical support (@James), who may be able to help answer some of your questions.



Thank you for flagging this - I raised it to our R&D guys just before the weekend and they should see that today, also we are in touch with Mirko directly by email too as we followed up on some similar comments he left on his product registration so his concerns are in hand…




There is a DC servo circuit inside the Rossini however it is part of the physical analogue output design and it is not a digital filter. As such it cannot be simply switched off by a firmware change.

There definitely are no pathological behaviours or significant phase shifting introduced by this filter and you are, of course, more than welcome to do the measurements to confirm this!