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Sound distortion when converting to MP3

 
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jurjenh



Joined: 20 Dec 2007
Posts: 1
Location: Ede, Netherlands

PostPosted: Thu Dec 20, 2007 11:07 am    Post subject: Sound distortion when converting to MP3 Reply with quote

I use my iPod as a dictaphone to record lectures. It registers in the WAV-format.
In order to be able to send these recordings by email to others, I convert them to MP3. It seems that whatever settings I use, the sound is always "enriched" with distortions, every cough or chair scraping changes into a hiccup.
Presently I use as settings for saving in MP3:
average bitrate
quality:2
bitrate 32
tags: id3v2.3
sample rate: automatic.
I'm rather tired of playing around with these settings, since I have little or no idea what they mean and the problem seems to pop up no matter what I do.
Anyone a suggestion how to reduce the size of my files in such a way that I can email them and they can be played at the average Windows-pc?
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CDJonah_alt



Joined: 15 Mar 2007
Posts: 378

PostPosted: Thu Dec 20, 2007 3:22 pm    Post subject: Sound distortion when converting to MP3 Reply with quote

Basically, these short, sharp sounds have lots of frequency bands, which
cannot be well simulated by a bit rate of 32 (32kbits per second).
Options that I see are:
1) Use a higher bit rate (and make the files proportionally larger)
2) Try to minimize the effect of the percussive events prior to making
the mp3
or
3) Learn to live with it.

I might try to
1) Normalize the sound to full scale
2) Follow by compression (AUdynamics comes to mind)
3) Follow by a bandpass filter to remove the highs.

Possibly 2 and 3 could/should be reversed.

Chuck

jurjenh wrote:
Quote:
I use my iPod as a dictaphone to record lectures. It registers in the WAV-format.
In order to be able to send these recordings by email to others, I convert them to MP3. It seems that whatever settings I use, the sound is always "enriched" with distortions, every cough or chair scraping changes into a hiccup.
Presently I use as settings for saving in MP3:
average bitrate
quality:2
bitrate 32
tags: id3v2.3
sample rate: automatic.
I'm rather tired of playing around with these settings, since I have little or no idea what they mean and the problem seems to pop up no matter what I do.
Anyone a suggestion how to reduce the size of my files in such a way that I can email them and they can be played at the average Windows-pc?




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Tristan



Joined: 13 Oct 2007
Posts: 30
Location: location, location

PostPosted: Fri Dec 21, 2007 11:01 am    Post subject: Eliminate unnecessary stereo channel? Reply with quote

(This may not be the source of your problem, but who knows?)

Even with the excellent LAME algorithms used by Amadeus to encode MP3s, a bitrate as low as 32 kbps will result in some ugly artifacts if you're encoding in stereo. Recordings of lectures, of course, generally don't need a left and a right. So make sure your files really have only one channel before saving to MP3.

Amadeus Pro makes it easy to downmix stereo into mono: select "Convert Track to Mono" (under the "Sound" menu) before saving the sound as an MP3.

All other factors being equal, the resulting mono MP3 will have the same file size, but will give you roughly 2x the sound quality of its stereo equivalent. Bye bye garbling. Cool

If stereo's not the issue, try an increased bitrate. 48 kbps will take up 1.5x the disk space compared to 32 kbps, but is quite a respectable bitrate for speech, especially in mono.

There is one quality-eroding mistake some folks make that I have to mention, though I'm sure you're not doing this. What NOT to do: save the sound as an MP3, close the sound, go away, eat lunch, come back, open the MP3 for further editing / EQ adjustment / etc, and re-save as MP3. This sort of iterative encoding needlessly deteriorates the sound quality a bit with every iteration. Always save uncompressed (AIFF, WAV, etc) until you're done editing, THEN save as MP3. Sorry, just had to say it while we were on the topic of troubleshooting MP3 quality.
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