Gary L Koh
CEO, Genesis Advanced Technologies
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Here are 2 more graphs. I've put a rectangle around spikes at approx 28k. This is more likely due to tape bias.
I've also drawn a black line and arrows across the spectrogram to show the tracks that are just upsampled.
and 2 more files where you can see noise at about 23.8k and 28k
Nice job, Bruce!
The biggest problem is likely the inappropriate (mis)application of windowing functions...
"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
Quite illuminating, Bruce. Thanks.
Guess this needs clarifying as such.
The colored spectrogram is based on on this bar graph.
The more amplitude you have, the more red the picture is.... the less amplitude.. the more blue.
This is better than a FFT graph because it gives you amplitude over a timeline, whereas an FFT doesn't. A FFT graph averages over a period of time.. Just like I showed you above. If it were not for the spectrogram, you would not be able to pick out the tracks of an album that were not hi-rez
I'd like you (Bruce B.) to post your graph of (any track from) Steely Dan's "Gaucho" album (HDTracks version), and compare it to any track from the "Aja" SACD. Gaucho has a dive in frequency response at about 20-21 kHz, and then a slowly rising (but very low) amplitude level at frequencies above that. Aja, OTOH, shows a smooth and gradual decrease in level all the way up to about 26-28 kHz without that rise afterwards. Since the original music is very similar in content, my interpretation is that there is an artificial low-pass filter used in the mastering of the HD (and/or DVD-A) version of Gaucho, and that it's really more like a 24/44.1 recording than a true 24/88 or 24/96 (as an aside, it looks almost identical to the spectral analysis from the Citizen Steely Dan box - all albums - except for some brickwalling of the DVD-A/HDTracks version). If there is a reasonable alternative explanation for that high frequency cut-off, I'd like to know what it is.