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While I was testing out the "Stereo Mix" tool on Windows 10, I had noticed that the output of Spek (after I rendered the audio file in Audacity using "Insane, 320kbps" preset and Joint Stereo) looked very patchy and jagged.

I had opened Spotify, found the song "After The Storm" by Mumford & Sons, then started the playback at about 2:10. After that, I had clicked record in Audacity (with Stereo Mix selected as the source of the audio) and recorded about 19 seconds of it. After that, I had directly exported the file using the settings I mentioned above, then immediately imported it into Spek. This is the output of the file:

Output of Spek

I have no clue to why it looks this way, so any help is appreciated. If you need some clarification, feel free to leave a comment.

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    I don't know why you're calling this "jagged", it looks exactly how I'd expect for the song and the algorithm on a linear scale. Can you explain what is wrong with it? – Marc W Feb 27 '17 at 18:28
  • Well, while even listening back to it, it sounded kind of crackly, and it looks as if someone took a cheese grater to it. Perhaps it's just because it's a section of a song, but the strange lines don't seem normal. – jramos775 Feb 27 '17 at 20:20
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lol, those "strange lines" (horizontal) are harmonics; and because this spectrogram is scaled linearly, they're evenly spaced; if it was scaled logarithmically, it would closer represent what we hear.
ATM, all of the detail is crunched down at the bottom, down past 6 kHz, which we actually hear as quite a high frequency.

I don't know about the crackling though. Does it sound very different to the original? If the original is a streamed file, then it will already be heavily compressed. If you compress it again, you are only losing more information and adding more artifacts (called 'generation loss'). Maybe this is what you can hear.

If you want the crackling to be looked into further, you would need to post the original 19 seconds of audio as well as the crackly 19 seconds and the logarithmic scale spectrogram (of both files, preferably) in a new question more focused on the crackling. But I suspect it's just a heavily compressed file.

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It looks like maybe there's some wideband noise or distortion prior to a gating device that suppresses it between phrases. Or maybe the noise was jumpstart derived from non-linearity in how the voice is handled. What is "Insane, 320 Kbps" supposed to do?

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