[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.