[PLUG] Resolved: Noisy mp3s

Richard C. Steffens rsteff at comcast.net
Thu Nov 15 19:26:13 PST 2012


> On Thu, 15 Nov 2012 12:03:31 -0800
> "Richard C. Steffens" <rsteff at comcast.net> wrote:
>
> Anyway, does anyone have any ideas about why the sound on my Linux
> machines show this noise while the sound on two Winders machines does
> not? And more important, is there anything I can do about it, other
> than listening on XP while typing on Ubuntu?

> <...>
On 11/15/2012 04:23 PM, Dale Snell wrote:
> Hard to say what this might be.  The only thing I can think of off
> the top of my head is that you've got clipping somewhere.  Try
> loading one of the errant files into Audacity and check for
> clipping.  If it's there, use Audacity reduce the audio amplitude;
> that should clear up the problem.

Bingo. I had to check the box, "Show Clipping" in the View menu, and it 
was obvious. Clipping was present every time one of the speakers spoke. 
I used the amplify effect to reduce the amplitude from 0.0 to -1.4 and 
the clipping disappeared. However, while quieter, the noise was still 
present in the saved mp3 file.

On 11/15/2012 06:40 PM, King Beowulf wrote:

> Rich, what linux audio player are you using?

I'm using a program called a python program called Transcribe. I get the 
same noise when using Movie Player. I'm guessing it uses the same 
underlying sound library as Transcribe, which uses gstreamer. 
Interestingly, though, the noise is not present when I play the audio 
with Audacity.

> You said you "clean up" the
> mp3 in audacity so is the sound quality bad in audacity or just another
> player?

I gave a wrong impression. I did not use Audacity to "clean up" this 
particular mp3. I have used Audacity for that purpose in the past, but 
not this time. It didn't occur to me to try since the noise sounds like 
an effect I get sometimes when filtering with Audacity.

> As Dale mentioned, clipping could be a reason. Also, if you
> didn't set up the noise filter properly you can have introduced some
> static that depends on the mp3 codec and player (Fraunhofer licensed vs.
> LAME for example).

LAME is what's installed here -- at least for exporting mp3s from Audacity.

> Also, you may wish to convert to a lossless format
> (wav or flac) before editing in audacity.  Also, consider mp3 bit rate,
> CBR vs VBR....

This proved very useful. I imported the mp3 into Audacity at the 
beginning of this exercise (responding to these e-mails). Since it was 
already there, I exported the file as flac -- after the amplitude 
reduction. Now it plays nice and quiet in Transcribe and Movie Player.

Thanks to both of you for your helpful ideas.

-- 
Regards,

Dick Steffens




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