Help with spectrogram of high res song

[aikofan]

I've been going through the high res files in my music library and trying to weed out all the upsampled ones. I'd like some help interpreting this spectrogram of a 96k/24bit FLAC, which shows a cutoff around 22k, but then there's a faint cloud of material roughly between 30 and 40k. What does this indicate? I'm guessing this isn't true high res, but I'm wondering what this ultrasonic stuff is--some kind of digital noise or artifact?

This album was downloaded from HDTracks in 2019.

 

[wwenze]

Probably aliasing from the original 44.1kHz content that wasn't completely LPF-ed

But yea if you're determining if it's upsampled then it definitely is, since real high res wouldn't have that gap at 22-24kHz

 

[aikofan]

Probably aliasing from the original 44.1kHz content that wasn't completely LPF-ed

But yea if you're determining if it's upsampled then it definitely is, since real high res wouldn't have that gap at 22-24kHz

Thanks, that's what I thought. I'm finding that at least half of the high res recordings in my library are like this. What a joke.

 

[Hayabusa]

Thanks, that's what I thought. I'm finding that at least half of the high res recordings in my library are like this. What a joke.

Also stunning is the 15.625 kHz tone most likely coming from a TV/monitor, so many recording have this fault

 

[Redacted]

There are a couple of tools that have been mentioned in this site (and more available online) that can batch process all your FLACs in one go and report if any are upsampled. Have a search - I think one member developed his own tool.

I use an old one called "LosslessAudioChecker 2.07" which works well, but this appears to be no longer available... You literally point this tool at a folder of music and it goes through the lot, showing status and making a report in a text file if you want. I can't be looking at spectra on each file!

None of the FLACs I have bought online or legitimately downloaded in the last few years have had an issue, but a few from friends trying to get me to listen to a new band have failed on every track! The common ones being being ADC from vinyl at idiotically high sample rates and bit depths - a 320 MP3 is arguably good enough for vinyl! But alarm bells ring when I see any at 24/192 on any albums, as big numbers are often the equivalent of click-bait...

 

[aikofan]

There are a couple of tools that have been mentioned in this site (and more available online) that can batch process all your FLACs in one go and report if any are upsampled. Have a search - I think one member developed his own tool.

I use an old one called "LosslessAudioChecker 2.07" which works well, but this appears to be no longer available... You literally point this tool at a folder of music and it goes through the lot, showing status and making a report in a text file if you want. I can't be looking at spectra on each file!

None of the FLACs I have bought online or legitimately downloaded in the last few years have had an issue, but a few from friends trying to get me to listen to a new band have failed on every track! The common ones being being ADC from vinyl at idiotically high sample rates and bit depths - a 320 MP3 is arguably good enough for vinyl! But alarm bells ring when I see any at 24/192 on any albums, as big numbers are often the equivalent of click-bait...

I've used Fakin' the Funk, which for me has been maybe 50% accurate, with many false positives but especially false negatives. I thought the Soniqtools online analyzer was more accurate, but you have to upload each file individually. After some trial and error, the quickest and most reliable method for me has been to just find all my 96k and 192k files via foobar2000 search filters, and then spot check the spectrogram of one song from each album using Spek.

I've found that just because I purchased a high res download from a legit site like HDTracks doesn't guarantee that it's not upsampled. But I've found classical recordings to be the most reliable. Kpop was been the least reliable, with almost 100% of 96k/24bit Kpop being upsampled, often from lossy sources with a hard limit at 20k or lower. Most of these are rips from streaming services, so paying extra for high res streaming seems like a waste of money.

 

[Redacted]

Yes LAC does give some false positives, but AFAICT it has never missed a true positive (although I have only tried a few albums using other means). The thing is, if you are checking a dozen albums at a time you can keep an eye on progress, and if you see one or two files in an album pop up as suspicious, you can check further or assume it's a false positive. Reissues that include 'new' bonus or live tracks are the ones that get tracks flagged most often but that's probably understandable. The main thing I look for is when every track in an album is flagged.

If anyone wants to try LAC, it's a 1MB portable executable, and I assume that since it was public domain free software for years, I would be at no legal risk of giving it to those interested, strictly for test and evaluation purposes.