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Old 19th December 2001, 02:54   #1  |  Link
MaTTeR
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Downmix type suggestion?

I've been digging a bit and really can't find an explantion to my question so I thought I'd throw it for you guys.

In some of the guides it's been suggested that you downmix to "surround" instead of stereo. When would I want to downmix to stereo? I'm looking for nice clean stereo/JS MP3 files that are seperated really well. In saying that, should I be downmixing my AC3 5.1 files to stereo instead of surround? Any advice or tips is much appreciated in advance.
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Old 19th December 2001, 11:37   #2  |  Link
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Good question .. let me try to answer it from my point of view .. i just hope it isnt rubbish i'm posting, i havent been able to investigate this any further :

When doing MP2 audio tracks for SVCD ( MPEG 1 Layer 2 ) at 224 kbps or higher i always use 'surround' mode, because some DVD players or TVs can detect the Dolby Prologic information and will give you DPL surround sound then, given your TV, DVD Player or Surround receiver have DPL decoding capabilities ...

For most of my DivX AVIs, especially 1 CD rips whith audio bitrates 100 - 130 kbps ( Lame ABR ) i use simple stereo because Lame should be used in 'joint stereo' mode for these low bitrates and my experiments showed that there was noise in the center and surround channels if DPL was encoded in such a low bitrate MP3 file, maybe because the joint stereo will result in deteriorated chanel separation and this can cause problems when the surround channels are decoded from the 2 channel using the known DPL matrix.

If you want DPL in your Stereo MP3 i recommend you try setting Lame to 'stereo' instead of 'joint stereo' and use bitrates > 150 kbps for your audio. VBR with q 2 .. 4 and --nspsytune should give nice results then.

Anybody with a better background concerning DPL in Stereo MP3 ?? I know Midas recommended to leave it a default, being surround ...
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Old 19th December 2001, 20:39   #3  |  Link
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Re:

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Originally posted by ChristianHJW
Good question ..
Good answer...
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Old 19th December 2001, 21:40   #4  |  Link
MaTTeR
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Re:

Quote:
Originally posted by ChristianHJW

If you want DPL in your Stereo MP3 i recommend you try setting Lame to 'stereo' instead of 'joint stereo' and use bitrates > 150 kbps for your audio. VBR with q 2 .. 4 and --nspsytune should give nice results then.
I just took one of the DD trailers, ripped the AC3 to MP3 with LAME (12-19-01 build)V2 --nspsytune settings. Average bitrate was around 247k and I forced Stereo mode. Also, I downmixed using Stereo in HEadAC3he. Played the sample on my Sony amp and it only plays at PCM 48k, never recogizes the DPL information. I've struggled with this for 2 months now. I'm just playing the RAW MP3 file via ZoomPlayer and WiMP8. Does it matter which player I use? Does the MP3 file have to be muxed with an AVI?

BTW- The sample did sound great as expected, it's just that my DPL light won't come on meaning my Sony AMP didn't see the DPL info.
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Old 20th December 2001, 13:27   #5  |  Link
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Re: Re:

Quote:
Originally posted by matter Also, I downmixed using Stereo in HEadAC3he. Played the sample on my Sony amp and it only plays at PCM 48k, never recogizes the DPL information
... did you downmix to simple Stereo ( 2 channel ) or to Stereo with DPL surround information ( 4 channels surround matrixed into 2 channels = Dolby Prologic ) ??
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Old 20th December 2001, 16:07   #6  |  Link
MaTTeR
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Re: Re: Re:

Quote:
Originally posted by ChristianHJW


... did you downmix to simple Stereo ( 2 channel ) or to Stereo with DPL surround information ( 4 channels surround matrixed into 2 channels = Dolby Prologic ) ??
Argh!!!! I'm ashamed :-) Let me run another test. haha
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Old 20th December 2001, 18:21   #7  |  Link
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Ok, went back and downmixed the Blade Runner AC3 for "surround" instead of "Stereo". I used LAME with Alt Preset Extreme to encode my MP3.

Here's the deal. I usually have my Sony amp set to auto detect the type of audio stream being fed to it. This mode seems to work the best for me while I'm watching DVD or DivX movies with AC3 tracks. Currently if I play an MP3 file in this mode, the auto mode only detects thatt he signal is a PCM 48k stream and NOT DPL. However, I started playing with the amp and discovered I could force DPL mode. I fired up the Blade Runner MP3 file and it sounded great in DPL. Voices were routed to my center speaker, surround speakers were doing an ok job as well and the sub to my amazement sounded like I was watching a DVD with an L.F.E channel. This really rocks! Thanks so much ChristianHJW for all the info. Now I need to test alt-preset normal and see how it sounds with DPL.

EDIT- One last thing. Am I correct in using "-m s" in order to force LAME to use stereo? Some have advised not to force stereo mode. Any thoughts? How about using --nssafejoint ? Encoding speed is never an issue for me, quality is though.

Last edited by MaTTeR; 20th December 2001 at 20:47.
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