[opendtv] Re: Precision

Which is probably how Dan's question could have been answered: you need to
sample the highest frequency that could be found in your (video or audio) AT
least 2x (per Nyquist) for each cycle at that frequency.  Preferably at
least 3x, if not 4x.  

John Willkie

-----Mensaje original-----
De: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] En
nombre de Allen Le Roy Limberg
Enviado el: Sunday, May 27, 2007 5:10 AM
Para: opendtv@xxxxxxxxxxxxx
Asunto: [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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