Skip to main content ↑ ↓

Notice

Please note that most of the software linked on this forum is likely to be safe to use. If you are unsure, feel free to ask in the relevant topics, or send a private message to an administrator or moderator. To help curb the problems of false positives, or in the event that you do find actual malware, you can contribute through the article linked here.
Topic: Weird visual noise band in the acoustic spectrum over 16khz (Read 1354 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.

Weird visual noise band in the acoustic spectrum over 16khz

So i have downloaded some flac files from some famous place. This is an album from the 90s. So i did what i always do and i bounced them off to Spek (you all know it). Here are the visual representations of two of the tracks. The rest of them also have the very same noise band within the exact same interval. You can see the images attached. I actually own this CD but i have no access to a cd drive so i can't check if the result would be the same if i ripped it myself.

The question is, can this be considered proof that these flac files are probably transcoded mp3s? Or, is there an actual chance that this is the actual representation of the original CD? And if that is the case, how could that be? This seems so wrong to me. Of course, i should probably mention that "i can't hear" anything weird when i play these files. They sound perfectly fine to me.

Re: Weird visual noise band in the acoustic spectrum over 16khz

Reply #1 –
Low bitrate lossy codec usually introduce spectral holes and complete cutoff of high spectrum, your attached pictures are global one and have whole song, to spot spectral holes you need much more detail that spek tool you used can not provide.

Re: Weird visual noise band in the acoustic spectrum over 16khz

Reply #2 –
I think you are right. I have downloaded another copy from a different source and it also has this oddity. I attached another photo and in this one, the audio data visibly goes all the way up to 22khz which i guess means that the actual CD had this weird band in it. I wonder how this happened.

Re: Weird visual noise band in the acoustic spectrum over 16khz

Reply #3 –
This is most likely shaped dither noise.
https://en.wikipedia.org/wiki/Noise_shaping
https://web.archive.org/web/20180418161004/https://sox.sourceforge.net/SoX/NoiseShaping
http://audio.rightmark.org/lukin/dither/dither.htm

Quote from: lovecraft on
The question is, can this be considered proof that these flac files are probably transcoded mp3s?
Lossy codecs usually remove noise, not add it.

Re: Weird visual noise band in the acoustic spectrum over 16khz

Reply #4 –
Quote from: Bogozo on
Lossy codecs usually remove noise, not add it.
There are also exceptions, e.g. subband codecs would add noise (modulated by signal), unless the given piece of a given band has noise floor above signal, then it's simply discarded and that's when it can be seen as also removing noise.
But there's likely almost zero chance running into a transcode sourced from those.
a fan of AutoEq + Meier Crossfeed

Re: Weird visual noise band in the acoustic spectrum over 16khz

Reply #5 –
I'm not looking on visual representations anymore but I'm used to do it more than 20 years ago. Many CDs exhibited this type of noise. I agree with Bogozo: it's likely dithering with noise shaping and I wouldn't worry about it.

What you see is definitely not an produced by MP3, AAC, OPUS, or MPC, nor WavPack (which adds HF, but not in that manner).

For a basic test: the original is 48 KHz, and after resampling and experimenting with dithering + noise shaping options, I obtained the second file. The noise in this file closely resembles the noise in your file.
Cheers
Wavpack Hybrid -c4hx6

Re: Weird visual noise band in the acoustic spectrum over 16khz

Reply #6 –
Also it has nothing to do with the FLAC subforum, even if someone uploaded it to the net in that format.
 

Re: Weird visual noise band in the acoustic spectrum over 16khz

Reply #7 –
Does that mean it was dithered first and then filtered? Talking about the attenuation at the very top
And so, with digital, computer was put into place, and all the IT that came with it.

Re: Weird visual noise band in the acoustic spectrum over 16khz

Reply #8 –
Quote from: Kartoffelbrei on
Does that mean it was dithered first and then filtered? Talking about the attenuation at the very top
https://web.archive.org/web/20180418161004/https://sox.sourceforge.net/SoX/NoiseShaping
http://audio.rightmark.org/lukin/dither/dither.htm
Looking at pictures by links above, you can see that some noise shaping algorithms have "attenuation at the very top".