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Distinguishing between lossless and lossy
Unrealmaster287
post Apr 27 2012, 11:44
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Hey,

I would like to ask a question about lossless audio. How can you distinguish between a lossless song and one which has just been converted into a lossless format but isnít actually lossless.

From what I understand you have to use a spectrum analyzer, but that is the extent of what I understand.

Thank you so much in advance wink.gif
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Arnold B. Kruege...
post Apr 27 2012, 12:24
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QUOTE (Unrealmaster287 @ Apr 27 2012, 06:44) *
Hey,

I would like to ask a question about lossless audio. How can you distinguish between a lossless song and one which has just been converted into a lossless format but isnít actually lossless.

From what I understand you have to use a spectrum analyzer, but that is the extent of what I understand.

Thank you so much in advance wink.gif


Doing what you want to do ranges from easy to mission impossible, depending.

The first thing I look for in detecting .wav or .flac files that have in the past taken a tour through the land of lossy encoding is a brick wall filter someplace around 16 KHz.

Here's a picture of what a spectrum analyzer shows with some lossy encoded files:

.

YOu can see a clear step or break in what would otherwise be a relatively gentle roll-off.

BTW this is from an earlier HA thread on a related topic. The specific post was provided by Cavelle.
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Unrealmaster287
post Apr 27 2012, 12:38
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Arnold B. Krueger, Thanks for the info, but the track i have has smooth drops and slightly sharp ones, IF I upload it here, is there any way you could provide some advice on whether it is lossless or not.

PS: How do I upload Images here

Thanks in advance wink.gif
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Brand
post Apr 27 2012, 13:01
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If you have the original lossless and a "suspect" file you can compare them. Based on the eventual differences you can pretty much certainly determine if the suspect is of lossless origin or not. (Not with 100% certainty, unless you know that there weren't any other lossless versions, like different pressings etc. or without taking into account ripping errors.)

If you only have the "suspect" file, you can never be sure of its origin. You can only make a guess with certain tools, like the spectrum analyzer, which will show you if there was a high frequency cut, which is typical for some lossy encodings.



QUOTE (Unrealmaster287 @ Apr 27 2012, 12:38) *
PS: How do I upload Images here

Upload the picture to some image host (like Tinypic). Get the direct link to the picture and post it with the "Insert Image" button.

This post has been edited by Brand: Apr 27 2012, 13:03
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Porcus
post Apr 27 2012, 13:27
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QUOTE (Unrealmaster287 @ Apr 27 2012, 12:44) *
How can you distinguish between a lossless song and one which has just been converted into a lossless format but isnít actually lossless.


(1) You cannot be completely sure. You can in quite a few cases verify that this hasn't been converted directly from a certain format to, say WAV without intermediate processing though.

(2) There are a few steps you can take in order to be more confident that the file is one way or the other.

(3) If you search this forum, you will find many old threads giving answers to (2) above. The most common answer is 'buy the CD and rip it yourself instead of pirating the track off the internet'.


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Unrealmaster287
post Apr 27 2012, 16:44
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Thanks for your help guys smile.gif
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db1989
post Apr 28 2012, 01:13
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QUOTE (Porcus @ Apr 27 2012, 13:27) *
(2) There are a few steps you can take in order to be more confident that the file is one way or the other.

(3) If you search this forum, you will find many old threads giving answers to (2) above.
Besides visual analysis, additional pointers: AuCDtect, TAU Analyzer, etc.

QUOTE
The most common answer is 'buy the CD and rip it yourself instead of pirating the track off the internet'.
But more so, this. Or even, perhaps, if you ask me(!), just forget about lossless and buy a lossy file from a digital distributor without pointlessly buying a CD, ripping it, and then leaving it on a shelf for however many decades before it gets landfilled. lalala.gif
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j7n
post Apr 28 2012, 02:10
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Besides a sharp cutoff, lossy encodes also have the upper spectrum in large, unmistakable chunks, that are encoded only when the signal is above a certain threshold, and rapidly appear and disappear during playback. Otherwise the cutoff is even lower. This screenshot shows a 320 kBit/s high quality MP3. Notice the missing chunk near 16k.

http://www.fileden.com/files/2012/4/26/3297107/juliasays.png

Even after moderate processing, such as a radio transmission, MP3 files can be recognized by this anomaly from streams that have merely been band-limited with a sharp digital filter.
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Rotareneg
post Apr 28 2012, 12:17
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lossless


mp3_V5


vorbis_Q4
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Porcus
post Apr 28 2012, 14:03
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QUOTE (db1989 @ Apr 28 2012, 02:13) *
Or even, perhaps, if you ask me(!), just forget about lossless and buy a lossy file from a digital distributor without pointlessly buying a CD, ripping it, and then leaving it on a shelf for however many decades before it gets landfilled. lalala.gif


Of course! The way to be sure whether your .wav has been decoded from an .mp3, is to buy the .mp3 and convert it to .wav! laugh.gif


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