Another upsampling/filtering question, this time involving Dirac room correction

[wgscott]

Although I have mostly redbook files, I also have some "higher resolution" files with authentic content beyond 22kHz.

My playback system is a Mac mini connected to a DAC (Teac NT503) via USB. I typically use Dirac Room Correction software, as a plug-in with Audirvana (playback software that allows the use of AU plugins as well as optional up-sampling and filtering. The Dirac AU plug-in can be run in such a way that it is the last to process the signal before being out-put to the DAC.

The room correction target curves (orange) I have generated always have a very steep drop-off around 17 kHz.


(click thumbnail for a bigger pic)

Does this sharp cut-off behave in essentially the same way that a (higher-frequency) redbook brick wall filter would behave, and if so, is it therefore more likely to produce audible aliasing artifacts? Would up-sampling (within the Audirvana playback software), prior to application of this filter, make this worse, or ameliorate aliasing artifacts? Should the window for the filter be adjusted so it only goes up to (say) 15kHz? Note that the actual signal above 10kHz is greatly attenuated to begin with (presumably my speakers and Class D amp are at fault). I can hear (barely) to about 15-16kHz, fwiw; certainly no higher. I am far more worried about the audible range than anything else.

 

[Blumlein 88]

Well it is 12 db or so in 3000 hz, so while steep it isn't brickwall steep. It could create "ringing", but the ringing would be above 17 khz. It is doubtful you could hear it. Even if you upsample, this filter will still act at 17 khz so I don't see that helping anything.

As for higher resolution files this filter doesn't create aliasing or imaging. Aliasing or imaging is when the material contains content beyond the upper level of the sample rate, and if not filtered out a mirror image is reflected into the audible band. If you were for instance playing a 192 khz file and this filter is at 17 khz, it doesn't add any content that would exceed the nyquist rate for 192 sample rates. If might ring above 17 khz, but no aliasing or reflected images from such a filter.