Unwanted frequencies in music files?

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I decided to learn some signal analysis with a spectrum analyzer. I have been using baudline as analyzer software.

baudline is able to display full spectogram or average levels of all present frequencies. user manual's exact explanation for averaging function: the average window is a way of collecting and displaying accumulated spectral traces.

i am using averaging function in order to get a summary of freq vs. level for a whole track. i detected extremely low frequencies (below 25hz) at some tracks :confused:.

track 1: a standard house music track. encoded in 128Kbps VBR MP3.
track 2: a test track from Ultrasone Test CD. it is a realistic image of a shore with sounds of soft waves, some breeze and birds. encoded with 16/44 FLAC.
track 3: a test track from Focal JMLab Demo CD 4. a trash metal song. encoded with 16/44 FLAC.
track 4: another house music track. encoded in 320Kbps MP3.


(all graphs are averaged and zoomed starting 0hz, displayed wrt the above order);

An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.


what is happening in tracks 2&3 :boggled::boggled::boggled: ?

just look at the freq band 0-50hz. it seems the encoded signal contains frequency below 25hz.

i also checked the regular spectogram (not the averaged graph) for the whole timeline of the track. those <25hz frequencies do exist along both of the tracks.

am i misinterpreting the graphs :confused: ?
 
i detected extremely low frequencies (below 25hz) at some tracks :confused:.

what is happening in tracks 2&3 :boggled::boggled::boggled: ?

just look at the freq band 0-50hz. it seems the encoded signal contains frequency below 25hz.

i also checked the regular spectogram (not the averaged graph) for the whole timeline of the track. those <25hz frequencies do exist along both of the tracks.

am i misinterpreting the graphs :confused: ?
CD Audio spectrum is DC to 22.05 kHz in theory. Perhaps some recordings do not limit the low frequency content, note these are test CDs.
 
I used to live directly over the road (80m) from the beach in north part of Perth, WA.
I can well assure you that there are some ultra/very low frequencies/pulses present in what seems to be quiet gentle surf sounds, and at surprisingly/disarmingly high amplitudes.
These ULF events are relatively rare compared to the VLF/LF events, and at 80m distance from the shoreline caused the house/surrounds/grounds to shake even on what seemed to be a calm and still evening.

I now live further north and about 800m from the shoreline.
On still, no wind nights (silent neighbourhood after 7.00 pm) these ULF/VLF events are also clearly audible/felt/sensed.
The rising ULF characteristic (LF pink noise characteristic) present in the Ultrasone Test CD (which I have and I am familiar with) shore sound recording you mention accords with 1/f noise/events present in nature and is also generated in semiconductors/passives.
In the shore sound recording you quote, the reasons for the such steeply rising ULF measure are not clear.
Looking at the ULF slope of your graph, I feel that there is a LF roll out of the mic/recording gear combined with real ULF audio signal combined with maybe some DC servo action.
I should have another close listen to that recording and see what I can subjectively discern.
Try researching 1/f noise....this is a subject in it's own.

Dan.
 
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Perhaps some recordings do not limit the low frequency content, note these are test CDs.

i found another one, this is Dire Straits/So Far Away; 16/44 FLAC, original recording (not a re-master). this is not a test recording :confused:.

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pls notice the low level, as it is known that Brothers In Arms (1985) has a low level (dBFS) in general. this is perfectly displayed on the average graph.
 
i have Audacity already installed. it has a Plot Spectrum feature. this is an excerpt from the documentation;

Plot Spectrum take the audio in blocks of 'Size' samples, does the FFT, and averages all the blocks together.

here is the analysis window shot from Audacity for Dire Straits/So Far Away with the same FFT size and window function selected.;

An externally hosted image should be here but it was not working when we last tested it.
 
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