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Topic: A pattern in spectral view (Read 6697 times) previous topic - next topic
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A pattern in spectral view

I decided to zoom in on a song with EAC's spectral view and this is what I found:



I'm curious to know what this is.  I'm assuming there's a term for it?

A pattern in spectral view

Reply #1 –
Moiré patterns.

A pattern in spectral view

Reply #2 –
Well, I knew that part.  I guess I want to know what it means when it's in a spectral view and why it happens

A pattern in spectral view

Reply #3 –
Quote from: Nuthen on
Well, I knew that part.  I guess I want to know what it means when it's in a spectral view and why it happens

They "aren't there".  It means nothing.
What you are seeing is an artifact of the way the data is displayed on screen.
I believe if you zoomed to a "1 to 1" zoom level you wouldn't see them, as the patterns are a result of no AA filter when subsampling a fine pattern.  (this subsampling is occurring because there is more data to display than you have horizontal resolution.)


EDIT:  Axon is right, it could be in either axis.  I don't know why I got it stuck in my head it must be the horizontal.
Creature of habit.

A pattern in spectral view

Reply #4 –
I agree - in this context it's going to be aliasing on one axis or the other.

A pattern in spectral view

Reply #5 –
It's just noise in the signal.
What exactly you don't understand in the spectrogram?

A pattern in spectral view

Reply #6 –
all it indicates is that there was a specific sound twice.

that sound was composed of several frequency components.

nothing unexpected.

A pattern in spectral view

Reply #7 –
(In regards to the last two posts)
Huh?
Creature of habit.

A pattern in spectral view

Reply #8 –
Quote from: Soap on
EDIT:  Axon is right, it could be in either axis.  I don't know why I got it stuck in my head it must be the horizontal.

Because the repetition is on the horizontal axis, it is more likely caused by aliasing on the horizontal axis.

What is the audio signal you used here? White noise?

A pattern in spectral view

Reply #9 –
Talking of stuff in spectrograms....

Here's an interesting one.
lossyWAV -q X -a 4 -s h -A --feedback 2 --limit 15848 --scale 0.5 | FLAC -5 -e -p -b 512 -P=4096 -S- (having set foobar to output 24-bit PCM; scaling by 0.5 gives the ANS headroom to work)

A pattern in spectral view

Reply #10 –
Sorry for the slightly off-topic post, but this composition by the Dutch composer Jurriaan Andriessen is not only a piece of music, the score is also a portrait of his wife Hedwig. Took him 6 years to finish.

[a href="http://www.jurriaan-andriessen.nl/index.php?pageID=16" target="_blank"]
 

A pattern in spectral view

Reply #11 –
Oh, I see. Such horizontal lines can be caused by comb filtering happening due to presence of delays.

A pattern in spectral view

Reply #12 –
Quote from: Alexey Lukin on
Oh, I see. Such horizontal lines can be caused by comb filtering happening due to presence of delays.

No, no, no.
The moiré patterns circled are an artifact of the way the audio data is displayed, nothing to do with the audio data itself.
Creature of habit.

A pattern in spectral view

Reply #13 –
Moire doesn't happen just because of data display. It arises from certain periodicities present in the data.

Do you see something similar when viewing this file in iZotope RX?

A pattern in spectral view

Reply #14 –
Quote from: Alexey Lukin on
Moire doesn't happen just because of data display. It arises from certain periodicities present in the data.

He's not at a 1 to 1 zoom - unless you can speak for the method of the decimation done in the software which created the image you simply can not say that.

Creature of habit.

A pattern in spectral view

Reply #15 –
I think I can, even w/o knowing about the exact decimation method.