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Author Topic: analyzing spectrum files  (Read 3824 times)

OfflineIrisRose

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analyzing spectrum files
« on: December 27, 2009, 02:25:52 PM »
I've used Audacity to do a spectrum analysis on three recordings.   One is definitely lossy; the second is definitely lossless, and the third???    I don't know how to read spectrum files, but I need to learn.  
How does one look at these files?  What information does one see to determine the quality.    I have to upload them separately, because the files all together are too big for one post.  
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OfflineIrisRose

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Re: analyzing spectrum files
« Reply #1 on: December 27, 2009, 02:27:49 PM »
Here is the lossy? lossless? graph.   If this post needs an explanation, please see opening post.
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OfflineIrisRose

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Re: analyzing spectrum files
« Reply #2 on: December 27, 2009, 03:35:43 PM »
bump
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OfflineHoops McCann

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Re: analyzing spectrum files
« Reply #3 on: January 01, 2010, 10:30:32 AM »
Here is the lossy? lossless? graph.   If this post needs an explanation, please see opening post.

Looks lossless to me. Looks like a bass heavy audience reocording too.

OfflineIrisRose

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Re: analyzing spectrum files
« Reply #4 on: January 01, 2010, 11:54:29 AM »
What in the graph shows you that it is lossless, Dan?   The torrent got banned on the tracker.   I had thought it was lossless, but someone else didn't.  What says "lossless" to you when you read it?   Is there a better spectrum analysis out there than Audacity--for free or cheap?   
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OfflineHoops McCann

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Re: analyzing spectrum files
« Reply #5 on: January 01, 2010, 01:02:42 PM »
What in the graph shows you that it is lossless, Dan?   The torrent got banned on the tracker.   I had thought it was lossless, but someone else didn't.  What says "lossless" to you when you read it?   Is there a better spectrum analysis out there than Audacity--for free or cheap?   

There's just a lot of activity above 15000 Hz that you wouldn't ordinarily see in a lossy file. Audacity is fine for FA. See here:

http://www.thetradersden.org/forums/showthread.php?t=4288

OfflineIrisRose

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Re: analyzing spectrum files
« Reply #6 on: January 03, 2010, 01:00:07 AM »
Thanks, Dan, I've spent a couple of hours yesterday and today reviewing the forum.   I've tested some new tracks using several programs to see the differences.   I still think my NHB recording was lossless, but the mods at the tracker think otherwise.     It is an audience recording, indeed.   How do you read "bass heavy" into it.  What part of the graph are you looking at?     Thanks for your help.   Much appreciated.
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OfflineHoops McCann

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Re: analyzing spectrum files
« Reply #7 on: January 04, 2010, 04:50:47 PM »
How do you read "bass heavy" into it.  What part of the graph are you looking at?

There are many more frequencies with a higher amplitude at lower frequencies (i.e. 1000Hz in your screen shot), than there are at 20000Hz and the higher frequencies under it. This is pretty typical in music recordings, however, in this case the graph is increasing fairly significantly if it is read right to left. In the past, I've found that this is pretty typical of audience recordings, which actually makes sense for other reasons that I'd rather not ramble on about here. Was I at least correct about this being an audience recording?

OfflineIrisRose

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Re: analyzing spectrum files
« Reply #8 on: January 04, 2010, 06:20:30 PM »
You are indeed correct about this being an audience recording.    I also think you are correct about its being lossless.    I ask because I want to learn from you.   I'll never be an expert on this sort of thing, but I want to be able to look at a graph and read it correctly.   In the last post, when I said, "reviewing the forum"  I meant Traders' Den.  The link you gave me was immensely helpful.   Thank you, Dan.   I appreciate the time you take.    :)
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OfflineIngo

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Re: analyzing spectrum files
« Reply #9 on: February 18, 2010, 12:20:24 PM »
I don't see any way at all to tell if a recording is lossless or not from a frequency spectrum file!  Both things are only related rather indirectly.

If you analyze the sound spectrum of an audience recording, you will see that it sounds bad, but this is obviously not because it is lossy but instead because it is an audience recording (recorded with a poor microphone in a big room).

So forget about this approach, it is nonsense and does not work at all!

If you want to decide if it is lossy you theoretically need to analyze if there are any typical artefacts coming from compression algorithms, but I doubt that this can easily be done.

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OfflineIrisRose

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Re: analyzing spectrum files
« Reply #10 on: February 18, 2010, 06:24:34 PM »
Thanks, Ingo, for your reply.    It is discouraging not to be able to determine lossiness then, without advanced equipment or software.  Then, I'll go back to the wave analysis.  There you can see the top and bottom cutoffs and the vertical bars that indicate some compression.   How does anyone, then, determine that only lossless files go onto dime, trader's den, and spanish city.   

I uploaded a file to spanish city a while back after looking at both wav and spectrum, and determined that it was lossless.   One of the mods said it was lossy and banned it, but then another mod said it was lossless and it got back on.   So when sound experts have a problem, how do the rest of us know. 

Thanks for any additional information you can give me.   
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Offlinedustyvalentino

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Re: analyzing spectrum files
« Reply #11 on: February 19, 2010, 06:14:21 AM »
The whole thing's a load of crap. Just listen to it, if it sounds good, it is good.
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OfflineHoops McCann

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Re: analyzing spectrum files
« Reply #12 on: February 19, 2010, 10:24:25 AM »
So forget about this approach, it is nonsense and does not work at all!

Nonsense? Doesn't work at all? I couldn't disagree more.

If you want to decide if it is lossy you theoretically need to analyze if there are any typical artefacts coming from compression algorithms, but I doubt that this can easily be done.

Visible in a spectral-type view of a wav file as shown here...

http://www.thetradersden.org/forums/attachment.php?attachmentid=2818&d=1109123983

OfflineIrisRose

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Re: analyzing spectrum files
« Reply #13 on: February 20, 2010, 07:16:19 PM »
Well, I spent several hours on Trader's Dean forums, checking out questions, comments, and screen shots.   There I learned exactly what Dan said.   
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Offlinepamplina

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Re: analyzing spectrum files
« Reply #14 on: September 26, 2012, 02:38:25 AM »
There're two programs I know to check lossiness (?):

Tau Analyzer: http://en.true-audio.com/Tau_Analyzer_-_CD_Authenticity_Detector
Audiochecker: http://www.softpedia.com/get/Multimedia/Audio/Other-AUDIO-Tools/Audiochecker.shtml

I think both do exactly the same test. The first is easier if you have the sound in CD, and the second can use directly FLAC audio files.
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