MP3 background noise artifact

Archived from groups: comp.compression,rec.audio.tech,alt.video.divx,alt.video.dvd (More info?)

This sounds like an interesting problem (no pun intended). So is this
an AC3 issue or an mp3 issue, I wonder? ...or is it an unfortunate
co-reaction where AC3 does something particular which is largely
innocuous in of itself, but it also happens to be something that freaks
mp3 out? Is it possible, this is clear indication of what the mp3 data
compression does to low level detail when in the presence of a much
stronger, dominating sound component? ...the key here being that this
time the low level detail is actually "musically" unrelated to the
primary sound, so there is no chance of masking? Just thinking out
loud here, so this is not necessarily a position I am arguing.

Archived from groups: comp.compression,rec.audio.tech,alt.video.divx,alt.video.dvd (More info?)

On a sunny day (9 Mar 2005 05:17:24 -0800) it happened "Yef" <e97y@yahoo.com>
wrote in <1110374244.950987.258950@z14g2000cwz.googlegroups.com>:

>Hi all,
>
>Recently I encoded some conversation to MP3 from AC3/DVD.
>In the AC3 source there was background noise: traffic,
>conversations, music. I have found that although the
>main conservation encoded to MP3 just fine, the background
>component sounds terrible. The traffic/music/talk are barely
>intelligible yet distorted, loud, and distracting.
>
>Is this an expected problem with MP3? I've tried
>increasing the bit rate to 160 and then 192 to get rid of
>it, but this doesn't seem to work.
>
>The source audio is AC3, and unfortunately I cannot
>pass-through the AC3 to avoid recompression with MP3.
>The program I am using produces an unusable AVI when I select
>AC3 as the output sound format.
>
>Thanks for any help.
AC3 has a compander / expander like mode.
In decoding the AC3 you should be able to set it so the background noise,
IF<<< it is a low level (much lower then the conversation), is more
attenuated then the conversation itself.
An special extra processing step can do this too, for example in Linux
the program 'sox' has a 'compand' effect option.
But you have to have some deeper understanding of audio to use all that stuff.
I have use expander / compander in the past to send stuff via telephone lines,
strongly reducing line noise...(or other people talking in background).
Higher bitrate does nothing for this sort of problem.
Also beware of high peaks, any clipping in mp3 (and AC3) will sound horrible
in playback, as teh codec will prefer the strongest signal, and enhance it.

Man I see you cross posted to half the audio universe, and video too.
Over to comp.compression, I am posting from alt.video.divx, these guys know
more about it then I do likely.

Archived from groups: comp.compression,rec.audio.tech,alt.video.divx,alt.video.dvd (More info?)

"Yef" <e97y@yahoo.com> wrote in message
news:1110374244.950987.258950@z14g2000cwz.googlegroups.com
> Hi all,
>
> Recently I encoded some conversation to MP3 from AC3/DVD.
> In the AC3 source there was background noise: traffic,
> conversations, music. I have found that although the
> main conservation encoded to MP3 just fine, the background
> component sounds terrible. The traffic/music/talk are barely
> intelligible yet distorted, loud, and distracting.

> Is this an expected problem with MP3?

I presume you first decoded the AC3 to .wav. So, tell us about the ,wav.

>I've tried
> increasing the bit rate to 160 and then 192 to get rid of
> it, but this doesn't seem to work.

Low level distortion is not a problem with MP3s of bitrates this high.