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Audio peaking after compressing down to mp3

 
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lilyokay



Joined: 20 Jan 2014
Posts: 1

PostPosted: Mon Jan 20, 2014 10:57 pm    Post subject: Audio peaking after compressing down to mp3 Reply with quote

I recorded an interview over Skype using Piezo, saved as an .mp3. Playback of the .mp3 file when opened in Amadeus Pro sounded perfect.

After making edits and saving it, still as an .mp3, it must have compressed down further and now it's peaking throughout (only in the channel with the guy's voice). Not realizing this could happen and carelessly, I saved over the original.

Is there a temp file of the original that's created when I open it in Amadeus? Because that would be ideal. Otherwise, any suggestions on how to make this audio salvageable?

Thanks very much for your help.

Screenshot of my waveform here: http://tinypic.com/r/25h1l03/5

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CDJonah_alt



Joined: 15 Mar 2007
Posts: 378

PostPosted: Mon Jan 20, 2014 11:28 pm    Post subject: Audio peaking after compressing down to mp3 Reply with quote

I once wrote a procedure in Igor (a scientific program) that could often
improve things. Looking at the screen shot, it might actually help your
file. Assuming I can find the code, I could try it on your data (I am
assuming that you don't have igor). Basically what I did was find the
clip sections, go either side of them and then fit a parabola to the
point on either side and then fill in the missing point (followed of
course by renormalizing the data. This assumes the clipping doesn't last
too long, etc.

Chuck

On 1/20/14 5:00 PM, lilyokay wrote:
Quote:
I recorded an interview over Skype using Piezo, saved as an .mp3. Playback of the .mp3 file when opened in Amadeus Pro sounded perfect.

After making edits and saving it, still as an .mp3, it must have compressed down further and now it's peaking throughout (only in the channel with the guy's voice). Not realizing this could happen and carelessly, I saved over the original.

Is there a temp file of the original that's created when I open it in Amadeus? Because that would be ideal. Otherwise, any suggestions on how to make this audio salvageable?

Thanks very much for your help.

Screenshot of my waveform here: http://tinypic.com/r/25h1l03/5






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630-252-3471 CDJonah@anl.gov

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dinojrx



Joined: 11 Nov 2009
Posts: 78
Location: Berlin / Germany

PostPosted: Mon Jan 20, 2014 11:43 pm    Post subject: Audio peaking after compressing down to mp3 Reply with quote

I fear, there's not so much to rescue. You can try to go down a bit with the level. May be trying the Normalize Effect (with -1 dB) will help. But at first (also for your next projects) save a copy as wav or in the amad file format. Then split both channels. So you can edit only one of them with effects. For cutting you can combine both again. In a final step you compress your file agin as mp3. Never save a sound multiple times as mp3. Every time you compress it, it will loose some (sound)information.

Jan


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No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.

Am 21.01.2014 um 00:00 schrieb lilyokay <forum2mail@hairersoft.com>:

Quote:
I recorded an interview over Skype using Piezo, saved as an .mp3. Playback of the .mp3 file when opened in Amadeus Pro sounded perfect.

After making edits and saving it, still as an .mp3, it must have compressed down further and now it's peaking throughout (only in the channel with the guy's voice). Not realizing this could happen and carelessly, I saved over the original.

Is there a temp file of the original that's created when I open it in Amadeus? Because that would be ideal. Otherwise, any suggestions on how to make this audio salvageable?

Thanks very much for your help.

Screenshot of my waveform here: http://tinypic.com/r/25h1l03/5






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JEGG



Joined: 24 Feb 2007
Posts: 121

PostPosted: Mon May 12, 2014 5:13 pm    Post subject: Reply with quote

It's normal (pun not intended) for lossy compression to raise the level. The amount varies according to compression and content. Sometimes it's only a fraction of a dBFS, other times much more.

So levels should always be checked after. Some dedicated converters (Codec Toolbox) will check for this and automatically reduce the file before encoding.

Especially if you're converting something complex, the conversion will sound better as well as not being clipped if you leave generous headroom. This can be seen by something (very expensive) like Pro Codec, or something lots less expensive like Codec Toolbox.

NOTE: Inter sample peaks can be significantly higher than peak levels, and can be seen on an analyzer that shows "true peak levels." Like the rise in levels with lossy conversion, true peak levels can range from a fraction of a dBFS to as high as a 1.5 to 2.5 in extreme cases. You can see this on an analyzer function similar to the one that gives waveform statistics in AP. (AP does not display "true peak.")

*IOW, if your peak levels are reading 0 dBFS, you are almost certainly clipping on playback, whether you hear it as outright or subtle distortion.*

Common theme: Leave significant room at the top. Way less goes wrong, and without fail it sounds better on playback.
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