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In Reply to: RE: A Proper Hi-Res File posted by John Atkinson on September 26, 2015 at 11:42:16
Here are four files that look suspicious to me. If you see any that you think are upsampled from a lower res copy, then please say so. I want to learn how to read these test results better.
Thanks,
Jamie
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Big speakers and little amps blew my mind!
Follow Ups:
> Here are four files that look suspicious to me.
Thank you.> If you see any that you think are upsampled from a lower res copy, then
> please say so.
None appeared to be upsampled.> I want to learn how to read these test results better.
What you are looking for is not the sort of gentle reduction in signal
level with increasing frequency that you are describing in your graphs
but the sharp cutoff at half the sample rate due to the antialiasing
filter. See the graph at the link below, which has two such cutoffs, one
at 16kHz and one at 22kHz, despite being a 96kHz file.
John Atkinson
Editor, Stereophile
Edits: 09/29/15
There is one more I would like you to take a look at, then I will leave you alone. I didn't include it, because I thought it an obvious upsample.
It has an almost vertical cutoff, but looking at it again it has a Fc of 26.1kHz, so it's past the halfway point for the antialiasing filter.
Your thoughts?
Thanks in advance.
Jamie
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Big speakers and little amps blew my mind!
Well, I guess that's what you call a brickwall filter. It is very much a filter. Nothing like I've tested so far. It shouldn't be too hard to spot in the future.
I will be more circumspect with my analysis from now on.
Wort was the lifeblood of JB wasn't it? :)
Thanks John.
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Big speakers and little amps blew my mind!
> I guess that's what you call a brickwall filter. It is very much a filter.
> Nothing like I've tested so far. It shouldn't be too hard to spot in the
> future.
Yes that sharp cutoff is is exactly what you should be looking for.
> I will be more circumspect with my analysis from now on.
Even so, your posting the graphs is very useful.
> Wort was the lifeblood of JB wasn't it? :)
I am not the world's best typist - the W and S keys are too close to
each other. for "wort" read "sort" :-)
John Atkinson
Editor, Stereophile
None of them look suspicious to me.
Here are some examples of what upsampled 44.1k looks like in SACD format:
http://archimago.blogspot.com/2013/07/list-suspected-44-or-48khz-pcm.html
Upsampled 44.1k in hi-res PCM format would look the same except without the ultrasonic hump in the noise floor above cutoff.
Dave, thanks for the input and the link. I will give it a another good look. Most of the brick-walls are very pronounced and some not. Chime in on a graph I post later if you want.
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Big speakers and little amps blew my mind!
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