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Lossy or Lossless? Please use this forum to post spectral and frequency analysis posts about shows you have your doubts about.

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  #1  
Old 2007-09-04, 02:02 PM
procella procella is offline
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Modern Day FMs

Somehow confused with modern day FMs. Almost all of them should be lossy, I know, but sometimes really not easy to tell if it's a good one by accident, at least for a learner like me.

First one is a 2007 BBC 1 broadcast (44.1 Khz). Looks rather good to me. But fa has a drop between 15 and 17 Khz.
Attached Images
File Type: gif BBC Radio1 fa.gif
( 10.3 KB, 32 views)
 
File Type: gif BBC Radio1 sa.gif
( 684.5 KB, 22 views)
 
File Type: gif BBC Radio1 sa2.gif
( 643.5 KB, 15 views)
 
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  #2  
Old 2007-09-04, 02:15 PM
procella procella is offline
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Re: Modern Day FMs

Second one is a 2007 KCMP broadcast. Can't see obvious signs for lossyness. But SA looks a little different than the BBC one. And FA takes a deep drop at 16 Khz but it's still at around -60db only.
('sa' is a complete song, 'sa2' 2 secs of it, carrier is at 19 Khz, cutoff at 16 Khz - information missing on the pics, sorry)
Attached Images
File Type: gif KCMP fa.gif
( 10.7 KB, 14 views)
 
File Type: gif KCMP sa.gif
( 694.9 KB, 8 views)
 
File Type: gif KCMP sa2.gif
( 676.0 KB, 8 views)
 
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  #3  
Old 2007-09-04, 02:26 PM
procella procella is offline
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Re: Modern Day FMs

Third one is a Spanish broadcast from 2004. FA looks quite similar to the last one. But the skyline in the SA has some strange cuts though they are not black. So I guess this should be lossy.
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File Type: gif Spain04-fa.gif
( 11.8 KB, 12 views)
 
File Type: gif Spain04-sa.gif
( 735.2 KB, 8 views)
 
File Type: gif Spain04-sa2.gif
( 708.5 KB, 10 views)
 
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  #4  
Old 2007-09-04, 03:16 PM
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Re: Modern Day FMs

Uh-huh.... and your point is what, exactly.........?

Regards, Graham
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  #5  
Old 2007-09-04, 03:59 PM
GIGFY26 GIGFY26 is offline
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Re: Modern Day FMs

My understanding:

Over the air FM received on a normal radio such as in your car is not a compressed signal. It is an analog Frequency Modulated radio wave. Digital data can be sent using Frequency Modulation as well but you wouldn't be receiving that unless you had a digital receiver.

Obviously this is totally independent of the original source that is being broadcast. If you play a mp3 on a FM station you would get a lossy recording and FA. Much the same as taking a mp3 and encoding to flac. Just because a torrent is in a lossless format does not mean it is a lossless recording. That's why FAs are often required and always appreciated.


And to my inexperienced eye, they all three look lossy. There are sharp drops below 15khz and the SAs all have a clear sharp line at the same level. These are often seen in mp3 sourced shows at these levels. This could be true for satellite and digital radio feeds as well depending on the compression ratio they are using.

I believe that if a mp3 source was broadcast over the air, that would account for the signal above the cuts and explain why there isn't more black above the sharp line in the SA.

Just my 2 cents
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Last edited by GIGFY26; 2007-09-04 at 04:07 PM.
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  #6  
Old 2007-09-04, 04:15 PM
GIGFY26 GIGFY26 is offline
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Re: Modern Day FMs

Also a quick follow up.
Analog signals can be and often are compressed before they are broadcast. This is different than digital compression used to save space and / or bandwidth.
In broadcasting, analog signals are often routed through compressors / limiters or clippers in order to prevent overmodulation.
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  #7  
Old 2007-09-04, 08:14 PM
procella procella is offline
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Re: Modern Day FMs

Thanks for these replies.

My problem is that I can't really decide often if it's lossy when it comes to FM. FA is clear but I guess not enough to be sure about it. SA cutoff seems to be a problem. Didn't think much about that sharp line. Was looking too much for bricks and holes, probably.
But I have still some questions. How could mixing FM and mp3 result in a signal above the cut when they both cut at around 16 Khz (somewhere 'Five' wrote that FM and TV cut like that)? Or doesn't this count for broadcast over the air?
And would the cutoff line look much different if a DAT and no mp3 was in the lineage?
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  #8  
Old 2007-09-04, 10:33 PM
GIGFY26 GIGFY26 is offline
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Re: Modern Day FMs

ok, this may get a little complicated.

I'm no expert but have worked in tv for a long time.

FM radio and tv audio, which also uses frequency modulation for it's audio, are two different but related things.
Frequency modulation is just a way of transmitting a signal. Think of it as encoding in modern terms. In AM, the amplitude of the radio wave changes to carry the information when compared to a baseline. In FM it's the frequency or the radio wave that is changed compared to a baseline. This is not to be confused with the frequency / channel of the radio or tv signal over the air which is a different thing and is what determines the baseline.

Lossy really just means that all of the original audio is not being reproduced. Mp3 and others, take into account human hearing and try to get rid of the frequencies [again another usage of the same word] that are "beyond the range of the average human hearing"

Answers to your questions to the best of my ability:
Different recording methods have different FA characteristics.
FA cut off just below 15khz is often indicative of mp3 for live recordings. I am not sure of broadcast specifications that cut there, but the info can probably be found at wikipedia or hydrogenaudio. For instance web broadcasts will have different specs than satellite radio which is different from digital radio etc.
The sharp line in the SA indicates to me an electronic clipping of the signal information.
If an original source has no information above 15khz [like a classic mp3] but is broadcast over the air on a signal that has a broader frequency range, there may still be information [ie noise even if you can't hear it] above the 15khz threshold.
Think of it as the broadcast coming down a pipeline. If the water flowing only fills the bottom half of the pipe there is still air and other stuff coming down the pipe above the water line.

I don't know that FM and TV cut at 16khz. I guess I could look it up, but I can pretty much guarantee that it varies around the world. I find it a little hard to believe that FM radio in the US and TV audio use the same thresholds but I could be wrong. Also if it's using compression and not clippers, I wouldn't think it would be such a hard line on the SA.
DATs also produce cutoffs of the frequencies but it varies depending on the mode [ie LP vs SP etc]. Mini Discs have yet another set of characteristics. Generally the DAT and MD recordings have drop offs at higher frequencies. Also variable bit rate mp3s cause even more gray area.

I've been told, and I believe it, that truly recognizing and identifying all the signatures of different recordings is as much an art form as it is science. That's why having as much lineage info as possible is crucial. For instance knowing it was originally a DAT in LP or a MD give you a great jumping off point. FWIW audio ripped from DVDs is a whole different set of specs. Some is lossy but some isn't.

Reading this back I'm not sure I really cleared anything up but it's a very complicated subject and while I am experienced, audio is not my specialty.

Hope this helps. I'm really try to learn to read these myself.

Disclaimer:
This is a limited, general and sometimes not totally technically accurate description of a complicated subject. I'm am not and will not be in a flame war but any constructive input is of course welcome.
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  #9  
Old 2007-09-04, 11:16 PM
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Re: Modern Day FMs

the cutoff is more abrupt in recent broadcasts, also the sound is very slurry like a lossy source... still, it would be expected to be able to see some blocky artifacts. I have noticed this with mainstream Toronto radio. If you could share a sample to rapidshare or similar I would like to take a closer look at it. I can also post SA screencaps for recent FM broadcasts I have taped & recieved. I can also contrast this with older (70s and 80s) broadcasts. btw I would be quite happy to discover that there is less lossy material being broadcast than I had previously estimated...
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  #10  
Old 2007-09-05, 12:16 AM
GIGFY26 GIGFY26 is offline
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Re: Modern Day FMs

Thanks for the info Five,

Did a quick google of some products and it does I see things like FM transmitter ranges of 20hz to 15 khz for the Orbands. I have to say that's surprising and a little disappointing. I always thought FM was a higher quality. I would guess and hope however that most stations run compression and not clippers. This would make it so the ratio from quiet to loud would stay intact but reduced and not just throwing info away. I'm not sure that would make a difference but it would make me feel better . I checked a few "FM" sources that I have for shows. For some reason EAC would only give me SAs of two and they fell of about 15khz but didn't seem as sharp as I have seen in some mp3s. The one that I could do a FA and SA, the SA still showed a dropoff around 15khz but the FA didn't show any sharp drop off. That seems a little weird.

Thanks guys. I hope we get a bunch of comments. I'm really trying to figure this all out as well, but I do feel it's a bit of a "guesstimate" sometimes. Again, that's where lineage can help so much to point us in the right direction.

Great Topic!!!!
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  #11  
Old 2007-09-05, 12:19 AM
GIGFY26 GIGFY26 is offline
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Re: Modern Day FMs

Five,

What's your take on the FAs and SAs that were posted above?
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  #12  
Old 2007-09-05, 12:53 AM
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Re: Modern Day FMs

Quote:
Originally Posted by GRC
Uh-huh.... and your point is what, exactly.........?

Regards, Graham
I'm with Graham on this one. New topic please.
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  #13  
Old 2007-09-05, 08:04 AM
procella procella is offline
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Re: Modern Day FMs

Quote:
Originally Posted by Five
the cutoff is more abrupt in recent broadcasts, also the sound is very slurry like a lossy source... still, it would be expected to be able to see some blocky artifacts. I have noticed this with mainstream Toronto radio. If you could share a sample to rapidshare or similar I would like to take a closer look at it. I can also post SA screencaps for recent FM broadcasts I have taped & recieved. I can also contrast this with older (70s and 80s) broadcasts. btw I would be quite happy to discover that there is less lossy material being broadcast than I had previously estimated...
Not much time at the moment. I will try to ul on Rapidshare later. Never done this before though. First example is FooFighters2007-08-17. I grabbed it from ZOMB but a slightly different version is on DaD also.
And I would really like to see your old and modern screencaps. Think this is one of the few things which are missing here. Information about FMs is spread over a lot of different threats.
From what I've seen so far I think you didn't overestimate the degree of lossyness in modern day FM. But I still have a lot of CD-rs to check.
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  #14  
Old 2007-09-05, 11:57 AM
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Re: Modern Day FMs

I'll get those up in the next few days, I'm also very busy!

Quote:
Originally Posted by GIGFY26
Five,

What's your take on the FAs and SAs that were posted above?
looks lossy but I would like to take a closer look & listen to find some more concrete evidence.

Keep in mind that TTD, DIME and sites in that vein still allow these broadcasts to be shared so long as they are taped from the open air, not from an internet or satellite radio source.
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  #15  
Old 2007-09-05, 12:46 PM
procella procella is offline
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Re: Modern Day FMs

Samples:

http://rapidshare.com/files/53613894/KCMP_sample.wav
http://rapidshare.com/files/53615745/BBC_1_sample.wav
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