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In Reply to: RE: Just get 192/24 recordings and play them as is. nt posted by fmak on October 12, 2009 at 10:15:38:
"Simple, I do FFT analyses of files; some so called hirez material have no content above 21kHz."
I don't think it is quite so simple.
Some program material itself doesn't have any content about 21 kHz. This will depend on the musical instrumentation, microphone type/placement and recording technology. I've looked at a lot of analog recordings on cassette tape, all known to have been analog mastered. Some of these have high frequency content as high as 23 kHz (on my Nak CR-7a). But others don't. Of course this can depend on the original recording. But the most recent remaster had content up to 23 kHz, as plotted on the Izotope RX display. This was only when a triangle was playing. With acoustic guitar and chorus there wasn't anything above about 19 kHz. I digitize these recordings at 88.2/24 and after any necessary remastering adjustments I downsample to 44/16 for CD release, using the 64 bit Izotope RX SRC.
If you run a SRC with a large window it will time average over a long period and will not capture high frequency energy in transients. For example, a piano recording will have high frequency energy above 20 kHz if closely miked, but only during the transient attack times. Most of the time the strings are simply decaying and their won't be much high frequency content. This is immediately obvious on the spectrographs produced by Izotope RX. If you use a large window on the FFT you will miss most of the transient energy.
IMO, a better way to detect fake hi-res is to look at the recording noise in the silent portions. (Not digital black, but actual room noise.) This will generally be broadband. You will be able to see artifacts of any filters used in resampling, e.g. a sudden drop in noise content immediately below 22050 Hz.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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Follow Ups
- Detecting faked hi-res from upsampled 44/16 - Tony Lauck 10:47:29 10/12/09 (1)
- RE: Detecting faked hi-res from upsampled 44/16 - fmak 21:56:12 10/12/09 (0)
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