Quantcast Two-Channel AC3 vs. MP2? - digitalFAQ.com Forums [Archives]
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11-02-2004, 01:14 AM
J-Wo J-Wo is offline
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I have some 2 channel AC3 sound from a 25fps source that I need to convert to 23.976fps. I generally use Besweet to do this, but is there any difference between chosing 2ch AC3 output vs. MP2 output? I ask because the output file size is the same between both formats. Also, if my source has 192kb/s sample rate, should I increase my output to 224 or leave it at 192 (bitrate is 48000 kHz for source and output)? Thanks guys!
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11-02-2004, 03:27 AM
Boulder Boulder is offline
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I don't know about BeSweet's ac3enc, but AC3 encoded with SoftEncode sounds better at the same bitrate as MP2 to my ears.
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11-02-2004, 04:00 AM
Dialhot Dialhot is offline
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Generally I use to say that MP2 or AC3 is just a "box arround the gift". And the box does not change the content.

But, according to Boulder's post, it's probable that AC3 is closer to MP3 than MP2. And it is generally admited than MP2 needs more bitrate than MP3 for an same "audible" quality : 160 for 128, 192 for 160...

So for your problem you will perhaps need to go to 224 if you want to use MP2. Now, I'm sure that at 192, you won't hear the difference.

Note: be carefull with besweet (or any ac3encode based programm) that lower the sound a lot !
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11-02-2004, 04:05 AM
Boulder Boulder is offline
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Also based on what SoftEncode tells me, for 2ch audio you should use 192kbps to keep all the higher frequencies. They start to cut already at 160kbps. With mono you're safe with 96kbps and above.
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11-02-2004, 04:51 AM
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- Till now "we" got no Problems when encoding mp2's at 128kbit when doing our KVCDs, so NOW when we do focus on DVD-R anyway its a good decision to make it better by rising the bitrate to for instance at least 160kbits.

- The problem of AC3enc.dll (out of liba52 FFmpeg core and so ffmpeg.exe also) is not the sound quality, its an issue of the bits treatment where some few player models do not support these resulted AC3s in a way of a proper playback.
Related to volume: If you add a normalizing like acid( -g max) then the volume is like the original AC3 from the orig DVD. And till now nobody in the world started a big topic about too low ORIG. AC3's

- Related to lower bitrates: There wont be a deeper cutoff in higher frequencies but a noticable distortion in higher frequencies which results in a "flanging" effect. Do encode a stereo signal using 96kbits mp2 and you will hear the high freq's but including that annoying flanging effect. Many people do interprete that as a "simple" cut-off of higher freq's but thats not the real mess.

So for me the resumeé is: IF using free encoding software, I choose mp2enc.dll in the case of 2.0CH output and azid.dll/AC3enc.dll in case of 5.1 input/output. - remember, we're talking about free software.

My player does not have any problems with AC3's delivered from the ac3enc.dll --- but thats like the way/sense as we choose our SAplayers for a proper KVCD playback (GOP up to 30 and non std. resolutions at mpeg1 video etc.) - and so that counts for our audio encodings too - as we're doing backups for our personal purposes.

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