Talk:Videos/A Digital Media Primer For Geeks

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Raw (digital audio) meat

Don't forget when talking about higher sampling rates that frequency and temporal response are inherently linked. One often overlooked aspect of this is the value of higher sampling rates in presenting subtle differences in multi-channel timing (e.g. the stereo field). Even fairly uncritical listeners presented sample audio blind can notice this. --Chaboud

They aren't merely "technically linked". They're mathematically indistinguishable. If a system doesn't has a response beyond some frequency it also lacks time resolution beyond some point.

To the best of my knowledge a perceptually justified need for higher rates is not supported by the available science on the subject. Not only is there no real physiological mechanism proposed for this kind of sensitivity, well controlled blind listening tests don't support it— well controlled being key, loudspeakers can suffer from considerable non-linear effects including intermodulation, and having a lot of otherwise inaudible ultrasonics can produce audible distortion at lower frequencies. Another common error is running the DAC at different frequencies— with the obvious interactions with the reconstruction and analog filters. A correct test for determining the audibility differences of higher sample rates needs to use a single DAC stage at the highest frequency, re-sampling digitally to create the bandpass... etc. I'm not aware of any such test supporting a need for information beyond 24kHz.

I normally suggest to people looking for increased to look into acoustic holography techniques like higher-order ambisonics and wavefield synthesis.

The beyond 48kHz sampling subject subject has been discussed a number of times on hydrogen audio, I recommend reading the thread there. They are quite informative. Most audio groups out there online and off are not very scientifically oriented (e.g. evidence based)— HA is special because it is one of the few that are.--Gmaxwell 06:00, 24 September 2010 (UTC)

Video vegetables (they're good for you!)

An interesting point is that the discussion of the linear segment in the normal display responses (e.g. sRGB) is incorrect, or at best incomplete, though I've coming up short on good citations for this, so Wikipedia remains uncorrected at this time.--Gmaxwell 05:15, 22 September 2010 (UTC)

Hi there, great tutorial, but in fact the most common DVD standard is 720 pixels by 480 pixels, with a pixel ratio of 0.9, yielding a device aspect ratio of 1.35. I understand that you're trying to simplify the lecture to 4:3 aspect (1.333) for newbies, I think this is ultimately misleading, since the vast majority of DVDs are not sampled at 704x480. --Dryo

Sort of-- the most common encoding is 720x480, but with the crop area set to 704x480; that's what the standard calls for (I was being sneaky when I said 'display resolution of 704x480'). Many software players ignore the crop rectangle and also display the horizontal overscan area. Many software encoders also just blindly encode 720x480 without setting the crop area. It is a source of *much* confusion. --Monty

"The standard" here being— Rec. 601? Is there anything else? We should probably at least link Wikipedia:overscan. --Gmaxwell 13:13, 24 September 2010 (UTC)

"[...] most displays use [RGB] colors [...]". Doesn't that sentence contradict this one : "[...] video usually is represented as a [...] luma channel along with additional [...] chroma channels, the color". I don't understand what "position the chroma pixels" means exactly. Are we talking of real points on a display ? Thanks, great video ! --Ledavulevogyre 13:59, 24 September 2010 (UTC)

General discussion

The video hasn't yet been formally released but we have all the sites up early in order to get everything debugged... Feedback on site functionality prior to the official release would be very helpful. --Gmaxwell 15:15, 22 September 2010 (UTC)

Released now, but still tell us about bugs :-) --Monty