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What kind of Ultrasonic Frequencies are in HD Tracks?

Discussion in 'Sound Science' started by bigshot, Jul 31, 2018.
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  1. bigshot
    These aren't my graphs, but a fellow poster here sent these to me because I was interested in seeing exactly what sort of content existed above 20kHz in 24/96 downloads. Take a look at these...

    This one is Brahms Piano Concerto No 2: Anna Malikova / Darlington - Allegro
    Nothing above 6kHz... except for a big old wad of noise between 60kHz and 90.

    Here's Mark Knopfler: Tracker 2015 - Laughs And Jokes And Drinks And Smoke
    A nice continuous tone at 55kHz that's louder than the music!

    Now, Norah Jones: Come Away With Me 2012
    A normal CD rolloff to 20kHz followed by a hump of high frequency noise and a spike at80kHz.

    Yes: Close To The Edge - Siberian Khatru
    Rolloff, noise hump, flurry of spikes.
  2. Arpiben
    Are those pics the spectrum of:
    1. digital audio distributed/purchased
    2. digital audio played in analogue and then recorded via ADC?
  3. bigshot
    These are spectrum graphs of HD Tracks that were purchased and downloaded. They were made using Foobar and the Voxengo SPAN plugin. The fella that found these tracks says this sort of thing isn't uncommon. On his system, the noise is inauduble, but when he buys HD Tracks, he routinely bumps them down to 16/44.1 to listen to. By the way, he says that those super audible spikes aren't short bursts. They are continuous tones throughout the whole track or album.

    Here is another one. This is John Coltrane: Alternate Takes Giant Steps


    He posted this one in the Testing Myths thread, but I guess everyone was too busy talking about LP cartridges and subconscious influences to notice it but me.
    Last edited: Jul 31, 2018
  4. Arpiben
    Well I noticed your posts and monkey of the sound ones (macacodosom) previously. But without the data and only a max hold spectrum picture not easy
    to provide valuable information.
    Anyway from a spectrum point of view only(not audio) ,those can be:
    • real stuff with noise picked up
    • FFT artefacts
    • artefacts caused by DAW.
    • artefacts caused in upscalng.
    Those in the industry will be in a better position to reply you and correct me.
  5. bigshot
    He offerred to send me the FLACs. If someone would be in a position to double check this, I could ask him for them. In any case, that stuff past 20kHz sure doesn't look Kosher!
  6. RRod
    Highpass the files past 20kHz and then use some kind of tempo plugin to bring things down 4-6 octaves while keeping the timing. That will let you hear what kind of material it is. I did this on one track recently and didn't find anything remotely tied to the music.
    llamaluv likes this.
  7. bigshot
    Do you think that they're introducing high frequency noise deliberately? Is there some theory that it doesn't matter what the super audible sound consists of? Is there any chance that you could post the pitched down noise track so I could hear what it sounds like? I'm curious.
    Last edited: Aug 1, 2018
  8. RRod
    I'll have to make it again but I can post a snippet.
    bigshot likes this.
  9. RRod
    Try this. One is the highpass, the other is the highpass dropped down 4 octaves (despite the name).
  10. bigshot
    Thanks! I have to figure out how to convert them to ALAC. Can't wait to hear these.
  11. pinnahertz
    @bigshot - you're on the Mac platform, right? Download VLC and play them direct as FLAC. When they say VLC plays everything, they're not kidding. There's no need or point to converting to ALAC unless you want to play them in iTunes, which isn't necessary for this. Audition will also open FLAC. VLC has a Media Information window that pukes it's guts about everything...code, bit rate and depth, the works.

    If you want to convert to ALAC in the MacOS Finder, select the file or files in the Fnder, control click, and choose Encode Audio File, then select Apple Lossless. You can do a batch if you like. It dumps them into the same folder as the original. Works for stripping audio from video files too.
  12. gregorio
    It depends on what you mean by deliberately? If you mean deliberately mixing in some noise to make it look like there's something potentially worthwhile up there, then probably not, although it wouldn't be completely unheard of! If you mean deliberately introducing noise in that ultrasonic range, in the sense of applying noise-shaped dither, then possibly, although noise-shaped dither isn't typically applied to 24bit files but it depends on the source material.

    Your spectra look fairly normal, although some of those ultrasonic spikes aren't particularly typical. When there are spikes like that, they're usually somewhat smaller and caused by some sort of electrical/EM interference (an unshielded video monitor for example).

  13. RRod
    I should note: these are peak normalized to 0dB. You can also try Audacity which will handle FLAC fine as well on Mac. This particular track has some of the weirdest HR material I've seen. You might also look at a spectrogram rather than just the averaged spectrum, so you can see if things change over time. Audacity and Audition will both handle that, as will SoX.
  14. danadam
    @amirm has a series on youtube where he examines hi-res tracks from a few different sites. IIRC each of them had some flaws.
  15. bigshot
    These things look bigger than some flaws to me. Gregorio, when I was doing restoration of 78rpm discs for CD release, the noise reduction filters did a good job of removing the noise and leaving the signal untouched. But the signal was so drastically narrow in response that the music sounded muffled. One of my tricks was to introduce low level high frequency hiss to fool ears into thinking the music contained frequencies that it didn't actually contain. I'm wondering if they think those little mounds of super audible sound past 20kHz will somehow make the track sound "better" than just going up to 20kHz. It also looks odd to me that almost all of these have a normal rolloff that would fit neatly into redbook. Then it comes back up for the mounds and spikes beyond that. Wouldn't that indicate that the original master rolled off normally in the mix and the super audible noise was added later?

    Thanks for the tips on playing back FLACs, Pinnahertz. I use Plex on my media server to play back most everything, but my computer isn't set up to play FLACs. VLC will be perfect.

    RRod, what song did these tracks come from?

    OHMYGOSH! I just played the pitched down track and I know EXACTLY what this is! It's the sound the Martians make in George Pal's War of the Worlds!
    Last edited: Aug 2, 2018
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