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#1
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MP3 background noise artifact
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. |
#2
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On a sunny day (9 Mar 2005 05:17:24 -0800) it happened "Yef"
wrote in .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. |
#3
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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. |
#4
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"Yef" wrote in message
oups.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. |
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