Which DAC Filter - Fast or Slow?

For me, slow. I mean, slow roll-off. 

headphone dongles, CD players that have that switch/option.

This means the waveform will extend to 20 KHz or higher,, then slowly roll off. A brick-wall filter would cut off right at 20 KHz. Anything above 20 KHz would be at 0 dB.

I use both on my dac because I can do it with a remote. It is easy to fit either slow or fast to any record as they all vary in tonality. Fast is best for any darker sounding record, slow best for bright records, simple as that. I will say that fast in my house of stereo results in a fuller, wider sound, but that can at times be so huge that it takes away from the locality of instruments and results to a less intimate sound setting. They both have their plus and minuses, which is why I would never have a dac without a remote.

I have an smsl su9 pro and I turn off all filters for a neutral filter is high fi in definition

I use mostly the slow filter, like 99.9999% of the time.

John Atkinson typically does nice thorough measurements of reconstruction filter responses in Stereophile’s DAC reviews. Here is a link to a high end Gryphon player measurements, showing the differences in the various filters. 

https://www.stereophile.com/content/gryphon-ethos-cd-player-da-processor-measurements

In my understanding a “fast” filter has a very steep low pass transition. Sometimes called a “brick wall” filter with virtually zero signal above 22.05 kHz (for 44.1 kHz sample rate).  This allows less roll-off below 20 kHz. 

Impulse response is one of the characteristics of different filters. Typically a “fast” filter will have significant pre-ringing which might sound unnatural. 

On the good side a “fast” filter generally reduces the chances of aliased artifacts being artificially created above the Nyquist Frequency (22.05 kHz for redbook). 
 

In my experience, some DACs have obvious sonic differences between their filter choices. Some not so much. 

Much depends on your amplifiers Sonic signature as well as speakers if you have say a neutral highly detailed beryllium tweeter ,then the fast filter can be too much 

of a good thing . I had a bit ofthis issue , I used different sonic signature f fuses 

for-example the  Audiomagic M1 fuse has a bit more Bass and more depth of image ,I used this for the dac, then took 3 Synergistic purple fuses for back of amplifier and 2 purple fuses for the ,very good  Linear tube Audio LPS going to the Sonore Optical Deluxe converters  which was a big step up in resolution and balance ,a bit morethen I wanted to spend but brought my streaming up a few notches.

Everyone's hearing is different. Pink 'em. Slow for me.

So far seems more are for slow filters! Anyone for fast?  Aside for @baylinor and I get your point.

Use both, like both, big band, orchestra, rock, fast roll off, pop, small ensembles, vocal, jazz, slow roll off.

From experience, I will add that for long sessions, slow is easier on the ears. 

Slow roll off is the best sounding in my opinion. 

I listen primarily through my Benchmark DAC3 HGC or the DAC3 B both of which have a 'fast' filter. Sounds great to me!

Finally, one that is purely on Team Fast…

Very interesting insights. And not what I expected (I expected more of a mixed bag of people liking slow or fast).

There is no right or wrong answer. The filter can be used to dial in the sound from your amp, your pre amp, and you speakers. It can also be source specific or it can be music genre dependent. For jazz and mid rock blues I like mid. For hard rock I like slow. Fast makes my system to bright even with tube engaged on my preamp. Also know my dac is Gustard R26 so it is also r2r ladder design. My most used setting is nos off mid filter and tube engaged on my Freya.