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looped file haunted by an elusive pop
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wxl



Joined: Apr 20, 2012
Posts: 14
Location: Cascadia

PostPosted: Sat Apr 28, 2012 9:46 pm    Post subject:  looped file haunted by an elusive pop
Subject description: i'm not saying it's aliens, but it's aliens
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this wav (a track by elizabeth veldon) was supposed to be part of her recent split with the man from ultra. the idea was to cut it from about 10" to about 2'41" and instruct people to put it on repeat on their media player. so she cut it in audacity and exported it-- and there is this nasty pop. i suggested that i would be willing to help her figure it out. so she sent me the wav.

i tried to recreate her experience in audacity and indeed found that even pre-export, looping (shift-space) a second of really any length in any position along the waveform resulted in the same problem. i tried trimming in sox and had the same problem.

the pop seems to occur after it loops but slightly beyond the beginning of the file. so i thought i'd look at a spectrogram (with sox), but no matter how i looked at it, i really couldn't find anything.

so then the idea was brought up to me to add a few milliseconds of fade in/out. makes sense as you'd have zero points. well i had one of two problems-- either there was too much and it sounded like there was a gap of silence-- or there was a pop. i was able to mimize but not fix it.

someone help me cuz i'm at a loss here but this seems like it should be pretty trivial.

this, by the way, is a copyrighted track as you can see. for the purpose of solving this problem, she has given me permission to share it but please be respectful and do not share it beyond this forum.

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PHOBoS



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PostPosted: Sun Apr 29, 2012 3:59 am    Post subject: transfinite numbers Reply with quote  Mark this post and the followings unread

well i looked at the wavefile and if you add the end and beginning together you'll see where (I think) the problem is.
Posted Image, might have been reduced in size. Click Image to view fullscreen.

so I cut a fraction of the start and end to where the wave goes through zero, which resulted in this.
maybe that's usefull. You can still here the transistion but that's probably because the sound itself isn't periodic.
There is a way to solve that; cut the file in half, swap the two parts around and do a crossfade where they meet.

(sometimes mediaplayers themselves can cause a bit of a pop too when looping a file)

edit: I think I might be the low frequency sounds themselves too that somehow create the pops.
if you skip through the file you get it at pretty much every point you start playing. (what is this alien device that produced this ?!)

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wxl



Joined: Apr 20, 2012
Posts: 14
Location: Cascadia

PostPosted: Sun Apr 29, 2012 2:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

as i said, i had a fade in/out that put both ends at zero. you did something different that got to the same ends. in both cases, it didn't fix it-- and it should have.

which sort of gets back to the original post. something very weird is going on here. as i understand it there's a bunch of layers that went into this piece-- i know no more about it. perhaps that's related?

i'm glad i'm not the only one who's puzzled.

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Muied Lumens
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PostPosted: Mon Apr 30, 2012 6:07 am    Post subject: Reply with quote  Mark this post and the followings unread

A few milliseconds of fade won't solve bass problems, and as Phobos says there is a fair amount of bass in there, with phase differences, in fact there is some sub-sonic bass in there too...

Beacuse of these issues I was unable to find a good loop too... You could keep on looking, or use a longer crossfade. In any case filter out the subsonics. Stereo bass with a chord on top is incredibly difficult to loop using zero crossings.

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Muied Lumens
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PostPosted: Mon Apr 30, 2012 6:18 am    Post subject: Reply with quote  Mark this post and the followings unread

Oh btw - by what you say it sounds like you are fading it out instead of crossfading... Try putting the file in a multitrack and crossfading there, then take a snippet of a working loop out of that. It will still pop as you start playing but if you really carefully cut it at the right places you should be home free.

Looping is nothing but nothing but trivial! Very Happy

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