D800E: moire and PP

Started Apr 25, 2012 | Discussions thread
Number 6
Forum MemberPosts: 51
Re: Artifacting and math
In reply to TOF guy, May 2, 2012

Thanks for the expansion, TOF guy.

"An AA filter in a typical dSLR has to start cutting before Nyquist so that it has some efficiency at Nyquist and prevent the worse artifacts. This is clearly visible on resolution charts in the dpreview reviews."
Ya works with what tools you got.

"And going back to your first point: that blur is also a distortion of the image."

Only the part that is below Nyquist, the rest can't be captured without a higher res sensor."

Strictly camera guys, skip this!

"With audio it's all benefit with very little cost. Therefore the anti-AA filter was bound to win. But it's not that clear cut - so to speak - with a dSLR."

(Effectively) true now, but it wasn't in the early days of CD. Pre-oversampling, analog filters cut below 20kHz.

"One can make very efficient low pass filters in electronics: filters which barely affect the signal before Nyquist and at the same time very effectively stop higher frequency harmonics."

You are correct about the effectiveness of "brick wall" filters in the audio world. However, correct me if I'm wrong; all audio recordings today are made using gently sloping low pass filters in front of DACs with sampling rates of 88.2, 96.0, or higher kHz. Mixing is done using these higher sampled frequencies and brick wall filtering is done digitally as the last step to 44.1k/48k data (higher for blu, SACD, etc.). As far as I know brick wall analog filters are never used (and rare and expensive anyway).

I've been using that very technology to convert some of my treasured LPs to digital audio. I sample at 88.2k, 24 bit, volume adjust and de-click there, then digitally brick wall to 44.1k 16 bit, using dithering and noise shaping. I can't hear the difference between final product and source LP. Yeah!

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