lossy or normal for FM?

[RaelEarl]

Hi,
I downloaded a Kansas show from 1979 which the seeder says to be FM and even explicitly states it has not been converted to mp3 and reconverted etc.

Can I be sure? I'm new to these things, so...I've learned a bit about the 16 kHz cutoff for mp3s. I've also learned that FM sources are lossy, is that right? This is the only recording from that show from that tour I know existing, so I hope this is OK.

Looking forward to you enlightening me.
Cheers

[paddington]

can't say if it's lossy (doesn't really look like typical mp3), but an FM recording will generally go up to about 15kHz (that's the limit of the transmission system). This looks different than that. Sometimes in FM recordings, you'll see the 19kHz stereo pilot tone, but not always. Dno't see that here, either.

[paddington]

just noticed you said 1979...

could this have been an AM recording and not FM? AM NRSC requirements cut the spectrum @ 10kHz (like this recording). This stuff at the top could be hiss from the tape, maybe?

[RaelEarl]

Originally Posted by jameskg

just noticed you said 1979...

could this have been an AM recording and not FM? AM NRSC requirements cut the spectrum @ 10kHz (like this recording). This stuff at the top could be hiss from the tape, maybe?

Yes, there is some tape hiss. Interesting what you say about AM. Perhaps the uploader just used "FM" as a synonym for "radio"...he says it was broadcast on a station called WLS FM as also interview snippets which are included indicate.

He says "This is the WLS FM radio broadcast, that was aired live as it happened on July 4, 1979.
As Robby mentions, it was going out live around the world, but a bad storm caused lots of
problems with the signal and this is rough. It is an FM broadcast, and although it is rough,
I have still enjoyed it for many years."

[paddington]

^^^ that may be it , then.

In 1979, WLS (AM) and WLS-FM were still mostly simulcast. There were some periods of the day that they were not, but that does, at least, make it possible that this was on BOTH stations and your recording may be from the AM.

If you want to upload a sample track somewhere I'll check it out to see if I can tell which transmission system it went through.

[RaelEarl]

Here is a sample track.
Thank you so much for your efforts.

[ragu421]

How does it sound? Are you happy with it? What else matters? If it is mp3 and you are happy with it, as long as you dont trade it and polute the "pool" who gives a shit.It's yours and you enjoy it soooooo listen away."Dust in the wind.All we are is dust in the wind".

[paddington]

Originally Posted by ragu421

How does it sound? Are you happy with it? What else matters? If it is mp3 and you are happy with it, as long as you dont trade it and polute the "pool" who gives a shit.It's yours and you enjoy it soooooo listen away."Dust in the wind.All we are is dust in the wind".

thank you , that's helpful.

[paddington]

Originally Posted by RaelEarl

Here is a sample track.
Thank you so much for your efforts.

ok, now the spectrum on this looks very different than the shots you posted above.



I turned up the brightness and contrast to see if there was anything else up there, but this track doesn't exhibit all the junk at the top of the spectrum your screenshots show above - also the wierd banding above 10kHz (that looked like electrical interferance) isn't present on this track, either.

The sound is pretty good for an off-air tape from nearly 30 years ago...

Now, here is that exact same segment with the contrast and brightness tweaked to show the darker (less-loud) audio info in the recording (same snip):




Notice that this basically cuts off at 10kHz. Everything is clean from there.

This is what AM radio does. The spectrum analyzer looks exactly as I would expect it to look for an AM broadcast.

Now, it may have just been a low-fi source being broadcast on both the AM & FM stations.

I notice your original poster said this:

He says "This is the WLS FM radio broadcast, that was aired live as it happened on July 4, 1979.
As Robby mentions, it was going out live around the world, but a bad storm caused lots of
problems with the signal and this is rough. It is an FM broadcast, and although it is rough,
I have still enjoyed it for many years."

If that is true, then I'd bet money what we have here is a 7.5kHz DATS monoaural satellite audio channel. The roll off weren't steep back then and you;d have this slight energy going a bit higher - as you can see in the SA, 7.5kHz is about where the most part of the audio rolls off.


Either way, it is NOT lossy - as in lossy digital compression (MP3, ATRAC, etc). It simply isn't full spectrum - but it is full spectrum for AM radio.



Question: this sample looks nothing like the samples you posted above.. are you sure those came from this recording? They really don't match at all - this track you sent me is much better than those.

[RaelEarl]

Thanks a lot for your efforts!

I should have said that my sample track was another one than the one I did the spectrum analysis on. Simple reason: The track I uploaded was smaller and thus took much shorter to upload than the rather long track I had analyzed myself.

But I also thought it would be interesting to compare different tracks from the same recording. Actually, with small differences they do look rather similar - not very much above the 5000 kHz mark.

So, looking at the categories in use here and at other forums, should I mark this as FM-sourced and then in my info file point to the fact that it is most probably AM or as you say a lo-fi pre-broadcast source?

Well, I've learned something new from you - thank you very much for sharing your expertise! This helps a relative newbie like me a lot!

Have a nice weekend!

[paddington]

I'm pretty sure this was an FM broadcast of a lo-fi satellite feed. No way to be sure, of course, but it definately isn't a victim of lossy digital compression or anything like that.

[Five]

yeah, I agree

could also be a poor cassette type (normal) and/or deck causing the lower cutoff.

Originally Posted by jameskg

I'm pretty sure this was an FM broadcast of a lo-fi satellite feed. No way to be sure, of course, but it definately isn't a victim of lossy digital compression or anything like that.

How much worse is a fm recording to a mp3 made from an official recording?
Oink rules says they wont let ppl upload fm recordings because they are not as good as mp3's.

[paddington]

Oink is wrong.

MP3 is lossy data compression that purposefully discards audio to save space. Who needs to save space anymore?

FM broadcasts are not lossy. They may roll off at 15kHz, but the audio below that is not lossy. Many stations compress the dynamics of their audio to compete with road noise in cars, etc (some do a terrible job of it, some do it well), but in 1979, it was as good as you could get. The spectrum roll off here is not because of the FM transmission system, it's because the source was lo-fi satellite or because the cassette wasn't full range, as Five said.