DAC Filters

[Gibsonian]

The mathematically ideal reconstruction filter is known (sinc) but impossible -- or at least inconvenient -- to realize. Therefore, approximations are used in DACs, with a careful weighting of what's more relevant vs. what is less relevant in practice.

When investigated thoroughly it turns out that the frequency response is the dominant factor. NOS and "Slow" filters have significant roll-off of the treble (up to several dB's by the time they reach 20kHz) and that is clearly audible as long as your hearing is still good to, say 15kHz and above... with source material that has enough content there (white noise preferred here as test signal).

The attenuation at fs/2 is way less important, as is the general attenuation above fs/2. Time-domain aspect (post-ringing only vs. pre-and post-ringing, or in other words, the phase response) is also not that important. And the higher the sampling rate the more so:

• Music seldom contains significant amounts of energy around, let alone above 20kHz.
• Any imaged components (frequencies mirrored at fs/2) are above normal hearing range for most people. With 48kHz or greater everything is 100% out of the hearing range of anybody in the world.
• Any downstream components that are not total junk will not produce any relevant additional intermodulation distortion products from the mixing of the images with the original content. And if they are junk, the normal IMD from signals below fs/2 is already dominating the picture, a bit more junk added doesn't have any real impact anymore.
• Any normal music signals also do not contain single dirac samples which would actually excite the ringing. But even when it is excited, it is at fs/2, so above normal hearing range.

Go here for a demonstration what different filters would sound like if we could hear beyond 80kHz.

Bottom line. Don't worry too much about DAC filters, and use the "Sharp" types which have the flattest frequency response. But even when using NOS, you can apply a bit of EQ to make it flat up to 20kHz and then the ususally reported differences don't expose themselves anymore.

For ADC's (Analog to Digital Converters), the filters are way more important as insufficient filters acctually corrupt the signals unrecoverably, adding aliased signals (stuff above fs/2 folded down below fs/2).

That’s how I roll typically. NOS and a little eq

 

[voodooless]

Just describing how the time-domain behavior of the Slow Roll-off filter affected my own listening.

You don’t know if the time domain behavior is the cause. Even if we concede that something it audible, It may just as well be the frequency response difference. You just assume it’s the pre-ringing. In any case Slow-Roll-Off still is not a good filter, not by a long shot! It will have basically no pre-ringing in the first place because of it.

 

[A Very Private Zootopia]

If you would have taken the times to look at the links provided, you would know that this is not so.

I used to assume the blur I heard with Slow Roll-off was mainly due to pre-ringing.

I mixed up the cause. Thanks for the clarification.

 

[voodooless]

phase/time-domain behavior

Does Phase Distortion/Shift Matter in Audio? (no*)

A viewer of my videos and member he suggested that I do a video commenting on a video that Paul McGown did on audibility of phase shifts. Here is Paul's video which was really about a different question (why we need wideband amplifiers) but turned it into phase being an audible problem: Here...

www.audiosciencereview.com

 

[RandomEar]

Whether you believe my experience or not is fine. I’m not presenting this as a test or a blind evaluation.

For context, when I was less familiar with DAC filters, I used a FiiO K9 ESS for a long time with the Slow Roll-off (linear-phase) filter, which involves pre-ringing. Over time, the sound consistently felt smeared and unfocused. I didn’t connect it to the filter at first, since I had forgotten which one was selected. (So it’s probably not just pre-ringing. Slow Roll-off filters can sound blurred for several time-domain reasons)

After revisiting the settings, switching to a minimum-phase filter resolved the issue for me. I’m not claiming universal audibility. Just describing how the time-domain behavior of the Slow Roll-off filter affected my own listening.

Slow roll off filters typically have very little pre-ringing and a drooping frequency response above roughly 14 kHz. The treble roll off is likely audible under specific circumstances. I think you're drawing conclusions based on some common misconceptions about DAC filters from subjective audiophile circles. I'm not saying there is no audible difference between filters - just not because of ringing.

 

[A Very Private Zootopia]

Slow roll off filters typically have very little pre-ringing and a drooping frequency response above roughly 14 kHz. The treble roll off is likely audible under specific circumstances. I think you're drawing conclusions based on some common misconceptions about DAC filters from subjective audiophile circles. I'm not saying there is no audible difference between filters - just not because of ringing.

I was mistaken in attributing it to pre-ringing.
Given how slow roll-off filters behave, the audible difference was far more likely due to the high-frequency droop.
Thanks for the clarification.

 

[Antiaudiophile]

Low dispersion on the Fosi ZH3 isn't bad for bright speakers. Either that or sharp roll off is best.

 

[markanini]

It's true that sharp roll off filters have higher theoretical chance of producing ringing over slower filters, even if this is counterintuitive. In practice though, most of the regular slow/fast filters work outside the audible frequency band and it doesn't matter which you chose.
The difference between linear vs. minimum phase filters is inaudible for the same reason, but the later is theoretically less susceptible to ringing. One consequence of minimum phase filters is that they alter the shape of the waveform. This is an inaudible in it self-see the youtube video below, but it might causes clipping to audio signals that were near 0dBFS. Most playback software and streaming service use loudness normalization so it's not a real-life concern. I'm excluding the ultra-slow filter modes that some DAC have, those should be avoided since the filter are slow enough to affect the audible band.

 

[Mentorron]

I have 2 SMSL C100 DACs with AK4493S chips. From initial research immediately after I installed them (photos 1 and 2), I have only tried filters 1 and 3 on the C100 so far (see photo 3 which I annotated by each basic description).
As I have tinnitus which hisses at about 9975hz, above which I hear nothing, and my hearing diminishes much before that, (see photo 4) I guess whatever difference I think I hear is my imagination ?