DVD-Audiobahn New DVD-Audio music releases and talk about the latest players.

---

[ Follow Ups ] Thread: [ Display  All  Email ] [ DVD-Audiobahn ]

---

[ Alert Moderator ]

---

Re "Aliasing" . . .

Posted by Martin419 (A) on September 8, 2005 at 03:23:31

In Reply to: Re: Thanks Martin for the info. Good job! posted by Christine Tham on September 7, 2005 at 15:09:28:

>> In one word, "aliasing". <<

Aliasing? But ONLY in terms of a reduction in resolution.
One shouldn’t overlook a very obvious analogy: Take a straightforward Windows photo bitmap (.BMP).

Now, using a very simple bitmap matrix editor, reduce the resolution by an uneven factor of say, 1.7. Now look at the picture: The result looks just looks fuzzy, and tainted by moire-fringes etc. (i.e. basically hacked to pieces and crap). In short: this is "aliasing".

Moreover, because of this aliasing, I would never use such a picture in aviation magazine I work for.

Now take the same large original image, and reduce the size (and hence resolution) by EXACTLY half. Of course the resultant picture looks smaller and some detail is lost, but it STILL looks clear and "right". And sure, I could happily use such a picture in my magazine if, say, the original file was too large in megabytes.

Conversely, if I DOUBLE the size of the image (i.e. scale it by EXACTLY 200%), and if also engage the "scale smooth" function, then it vector interpolates into the added data points. And the result "looks" good. No obvious artefacts. Funnily enough, if I then EXACTLY halve it again, it seems to leave me with an image which looks every bit as good as the original. Again, no obvious artefacts.

Well this applies if you were to depict part of a PCM wave section as a visual bitmap (indeed, I've seen this on digital wave-capture scopes on my computer which can do this easily). Now, if I exactly halve the resolution (i.e. by parsing through it to simply take out every other data column), then the new wave file still looks and sounds as "good" as it can possibly be AT THE NEW RESULTANT LOWER RESOLUTION.

In contrast, if I DON'T scale the wave by exactly even multiples (either up or down), then it NIETHER looks good on the scope matrix, NOR does it sound good when played back.

Anyway, the proof is in the pudding. I have the R.E.M. greatest hits DVD-A. The stereo Group 2 tracks are interpolated & upsampled by factor of four to 192kHz. Now if I tell my player to downsample to 48kHz, it still sounds as good as the corresponding tracks on the "Automatic For The People" DVD-A (which is presented in native 48kHz).

Now, coming back to BIA in 5.1. I don’t think all this digital aliasing stuff matters too much, since Ainlay & Knopfler took the direct analog outs from the DASH. So, I agree with you, Christine, that Ainlay took the very best approach possible given the material he had to work with. And the end result is a superb 5.1 mix of this classic album.

This post is made possible by the generous support of people like you and our sponsors:

Parts Connexion

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---