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16/44 FLAC vs. AAC 256


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Hi. So today I bought the same track from 2 sources... iTunes and 7Digital.

 

I used the tool SPEK to analyze the waveforms:

 

Here's what I got from iTunes -- 256 AAC

1-03 Bananza (Belly Dancer).m4a.png

 

and here's what I got from 7Digital -- 16/44.1 FLAC

Akon - 03. Bananza (Belly Dancer).flac.png

 

How do I interpret these charts?

 

thanks

 

--jay

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Looks to me they are both lossy and identical. Just because they say it's flac doen't mean it is.

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Don't feel bad. I recently bought a track on Pono and it was also obviously lossy rewrapped flac. You can tell when it's cut off below 22hz, a telling sign of lossy.

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Don't feel bad. I recently bought a track on Pono and it was also obviously lossy rewrapped flac. You can tell when it's cut off below 22hz, a telling sign of lossy.

 

How, given that RB CD has a cut off below 22.05 kHz? (44.100kHz/2)

I presume that you meant 22kHz.

 

Jay

Out of curiosity, how did the file sizes compare after you decoded the .flac file ?

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

PROFILE UPDATED 13-11-2020

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Looks to me they are both lossy and identical. Just because they say it's flac doen't mean it is.

No, they are not identical at all. In the first picture, lot of harmonic is missing, from time mark 0:20 to the end. Both have cut-off @22kHz, so we can't say the FLAC is from lossy file.

Sorry, english is not my native language.

Fools and fanatics are always certain of themselves, but wiser people are full of doubts.

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Hi. So today I bought the same track from 2 sources... iTunes and 7Digital.

 

I used the tool SPEK to analyze the waveforms:

 

Here's what I got from iTunes -- 256 AAC

[ATTACH=CONFIG]22859[/ATTACH]

 

and here's what I got from 7Digital -- 16/44.1 FLAC

[ATTACH=CONFIG]22860[/ATTACH]

 

How do I interpret these charts?

 

thanks

 

--jay

I don't think you can tell just by comparing these plots. The files are clearly different (there are small differences in the plots) so bit for bit identical they are not.

 

It is actually an interesting question: How to assess whether a compression method such as aac has actually destroyed data?

 

Additionally, you're just looking at a frequency spectrum, no phase info, and to be honest even the spectrum height is hard to discern here since it's signaled by color.

 

There has got to be a measure of preserved detail or similar. Perhaps analyze the spectrum and phase of the difference, but you need to make sure to properly align the data.

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There isn't much to see on those images, but maybe you'll see something if you zoom in on the time axis.

 

Here's an example of a five-second segment to show typical artifacts of AAC 256:

 

Original (24/48):

Screen Shot 2015-12-20 at 1.04.27 PM.png

 

AAC256:

Screen Shot 2015-12-20 at 1.07.45 PM.png

 

The lossy file was lowpassed at a hard frequency cutoff of 21.8kHz, and analyzed into time-frequency windows. You see a patchwork pattern of little black squares where the encoder found no audible content and little green squares where it found a little.

 

The OP's FLAC file seems to have been created with an antialiasing filter that has a 20.5 kHz cutoff. As a result, a 21.8-kHz lowpass would have no perceptible effect. (Common MP3 encoders have a 20.0-kHz cutoff at high bitrates, and 16kHz or so at lower bitrates. You would notice the effect of those on a spectrogram. That no doubt is what ElviaCaprice was referring to.)

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Looks to me they are both lossy and identical. Just because they say it's flac doen't mean it is.

 

They aren't identical. Look again. You can't always just look at it and see it has been compressed. If the AAC compression did it right, it should be very difficult to hear a difference, let alone see differences in the spectra.

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Hi. So today I bought the same track from 2 sources... iTunes and 7Digital.

 

I used the tool SPEK to analyze the waveforms:

 

Here's what I got from iTunes -- 256 AAC

[ATTACH=CONFIG]22859[/ATTACH]

 

and here's what I got from 7Digital -- 16/44.1 FLAC

[ATTACH=CONFIG]22860[/ATTACH]

 

How do I interpret these charts?

 

thanks

 

--jay

 

The dark patches in the first chart are a telltale sign of lossy compression.

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They aren't identical. Look again. You can't always just look at it and see it has been compressed. If the AAC compression did it right, it should be very difficult to hear a difference, let alone see differences in the spectra.

 

The differences are usually much easier to see than to hear. That's kind of the point.

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so admittedly I don't have an original CD to do an absolute comparison... but why is there what looks like a horizontal line at around 16khz? It looks to me like both files have the same horizontal line which I thought indicates a cutoff endemic of lossy compression.

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Usually a line around 16kHz indicates that there was a video camera or monitor in the room

(TV)Monitor, yes this is possible (if it is CRT type), a camera... not very likely I think.

Sorry, english is not my native language.

Fools and fanatics are always certain of themselves, but wiser people are full of doubts.

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well, the physical CD arrived and I ripped the track to WAV (just to make it easier to see in graph comparison, there's no diff between FLAC and WAV)

 

flac_download_vs_ripped_wav_compared.png

 

Looks to me like the download FLAC from 7Digital is identical to the ripped WAV, which means 7Digital is selling legit lossless music. The AAC from iTunes is different. Thanks to everyone here who helped with this analysis.

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well, the physical CD arrived and I ripped the track to WAV (just to make it easier to see in graph comparison, there's no diff between FLAC and WAV)

 

[ATTACH=CONFIG]22922[/ATTACH]

 

Looks to me like the download FLAC from 7Digital is identical to the ripped WAV, which means 7Digital is selling legit lossless music. The AAC from iTunes is different. Thanks to everyone here who helped with this analysis.

 

Legit to them in that this was provided to them as is to be sold, doesn't mean it's legit redbook. From the graph I'm still in the camp that it is not. Could also be a poor recording. How does it sound to you?

(JRiver) Jetway barebones NUC (mod 3 sCLK-EX, Cybershaft OP 14)  (PH SR7) => mini pcie adapter to PCIe 1X => tXUSBexp PCIe card (mod sCLK-EX) (PH SR7) => (USPCB) Chord DAVE => Omega Super 8XRS/REL t5i  (All powered thru Topaz Isolation Transformer)

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Looks to me they are both lossy and identical. Just because they say it's flac doen't mean it is.

(From Post 2.)

 

Don't feel bad. I recently bought a track on Pono and it was also obviously lossy rewrapped flac. You can tell when it's cut off below 22hz, a telling sign of lossy.
(from post 4.

 

Legit to them in that this was provided to them as is to be sold, doesn't mean it's legit redbook. From the graph I'm still in the camp that it is not. Could also be a poor recording. How does it sound to you?

 

Are you now claiming that the purchased CD was manufactured /derived from a "Lossy" copy of the original recording ?

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

PROFILE UPDATED 13-11-2020

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Sure looks like it. Or the original recording was done lossy?

Hard to say with jaynyc's software screen shots. I would feel better with some RX shots. Oh well, how does it sound? That would be another tell. Obviously the op felt concerned about it enough to make this thread, SQ.

 

Then again I could be wrong, which wouldn't be the first time and I'm willing to admit unlike some folks. chuckle

(JRiver) Jetway barebones NUC (mod 3 sCLK-EX, Cybershaft OP 14)  (PH SR7) => mini pcie adapter to PCIe 1X => tXUSBexp PCIe card (mod sCLK-EX) (PH SR7) => (USPCB) Chord DAVE => Omega Super 8XRS/REL t5i  (All powered thru Topaz Isolation Transformer)

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I would argue that you can't tell from these images if the FLAC and CD are lossy sourced or not. All we can say with some degree of confidence is that a CRT monitor or other device with a flyback transformer was turned on and in range of a microphone when the recording (or at least one track of it, assuming it's a multitrack mixdown to stereo) was made.

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Then again I could be wrong, which wouldn't be the first time and I'm willing to admit unlike some folks. chuckle

 

Just make sure that you don't fall into the bigger hole you are digging for yourself in this thread!

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

PROFILE UPDATED 13-11-2020

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Just make sure that you don't fall into the bigger hole you are digging for yourself in this thread!

 

No hole here other than the witnessing of your own ego and it's need to be fed on this forum!!

(JRiver) Jetway barebones NUC (mod 3 sCLK-EX, Cybershaft OP 14)  (PH SR7) => mini pcie adapter to PCIe 1X => tXUSBexp PCIe card (mod sCLK-EX) (PH SR7) => (USPCB) Chord DAVE => Omega Super 8XRS/REL t5i  (All powered thru Topaz Isolation Transformer)

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No hole here other than the witnessing of your own ego and it's need to be fed on this forum!!

 

This thread has clearly demonstrated just how little you really know.

It would appear that the Pope blessed the wrong end ! (chuckle)

 

Bye !

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

PROFILE UPDATED 13-11-2020

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Sure looks like it. Or the original recording was done lossy?

Hard to say with jaynyc's software screen shots. I would feel better with some RX shots. Oh well, how does it sound? That would be another tell. Obviously the op felt concerned about it enough to make this thread, SQ.

 

Then again I could be wrong, which wouldn't be the first time and I'm willing to admit unlike some folks. chuckle

 

Elvia-- I used Spek (Spek – Free Acoustic Spectrum Analyzer / Spectrogram Viewer). What is better (or best) software to use to do this type of visual confirmation analysis?

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