[opendtv] Re: Precision

"Aliasing" is used to describe what happens in digital video when it is
sampled at a rate less than twice its highest frequency.  The undersampling
of the high frequencies creates spurious low-frequency components.  The
phemenon is sometimes referred to as "frequency-spectrum folding".

Al
----- Original Message ----- 
From: "johnwillkie" <johnwillkie@xxxxxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Saturday, May 26, 2007 1:20 PM
Subject: [opendtv] Re: Precision


> Sure, "aliasing" first entered the video lexicon when people tried to put
> graphics on top of video, or tried to superimpose video.  Those come from
> the 1950's and 1960's, perhaps earlier.
>
> Audio aliasing wasn't something that I heard about until the mid/late
> 1970's, when PCM encoding (u-law and A-law) and quantization error came up
> against analog audio as the input source and output target, with PCM in
> between.
>
> John Willkie
>
> -----Mensaje original-----
> De: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] En
> nombre de negrjp
> Enviado el: Friday, May 25, 2007 2:52 AM
> Para: opendtv
> Asunto: [opendtv] Re: Precision
>
> Very Interesting!
> In video domain is possible aliasing phenomenom?
> For LP records nostalgia, Look this :
> http://www.elpj.com/index.html
>
>
>
> Jonas
>
> In video, how much precision is enough?
>
> Let us take audio as an example. Audio can be sampled at 48,000 samples
per
> second, 16 bit, and it is "CD" quality. But sample at 192Khz at 24 bit,
> process, downconvert, encode, etc., and the quality is markedly better
than
> when produced at the previously stated format. Of course, we are only
> dealing with one axis, representing pressure, and time (or are we?).
>
> However, if we sample audio at 384Khz at 48 bits, I bet not but three
people
> in the world could tell a difference from the audio produced at 192Khz at
24
> bits. So there is a point to which we have human limitations and there is
no
> reason to sample higher or with more "precision" (Law of diminishing
> returns), save research areas.
>
> However, there is a weak link to this aforementioned audio recording:
> spatial offset. Even with 7.1 surround sound, there is still spatial gaps
to
> fill with audio. So there is still room for improvement. But it is not in
> sampling frequency or bit depth that will make the difference.
>
>
>
>
>
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