Sound differences with AC3filter

[fluffykeith]

Hi

Basically I am interested to know why an mpg created usng VCDGear (extracted from a VCD) has sound that only comes out stereo when passed through AC3filter but the sound from my recordings AC3filter can changes to surround.

What do I need to do to AC3filter to get the vcd extracted mpeg in surround without messing up - for example MP3 which should remain stereo?

Cheers

Keith

[JonnyCam]

I'm not sure I understand what you are asking.

Are you looking to get surround sound from the VCD audio track, or trying to stop it from being in surround?

Oh - if it's not coming as surround maybe you have MPEG audio set as passthrough int he AC3filter config> (so it's passing 2 channel mpg audio, as-is. On the recordings it may be apply the surround alogrithms. (not sure why, maybe it doesn't recognise MP2 as mpeg audio? - what is the audio format of your recordings?)

Now, if you want to get an actual "surround" track and not just when applied by Ac3filter at play-time, then I suggest you download BeSweet (& BeSweet GUI) and have a go with that - it allows you to transcode your MP3 / MP2 audio tracks to 5.1 AC3, which could then be re-muxed into your MPEG-1 video file.

EDIT: Reading your q a bit more, I see what you mean - you want surround from the mpeg track, but not when playing normal mp3 music. I use a registry command to switch the SPDIF output on or off, linked to custom tasks in PVRX2. (as I cant hear anything on the tV when SPDIF is enabled if I dont have my amp on)
You could do the same for 5.1 or 2/0 speaker output - have One command for "set stereo", and one for "set multi channel"
I'll find the reg commands and post them.

[JonnyCam]

Ac3filter registry settings:

[HKEY_CURRENT_USER\Software\AC3Filter\preset\Default] -- No space in default here, the forum keeps adding...

the "mask" key can be changed to change the output format.
A decimal value of 5 in there will give you 2/0, where a decimal of 63 will give you 3/2+SW. (63 = 3f in hex, which is what has to go into the file)
0 will leave the audio as-is.

use_spdif : 1=on, 0 =off

You can use the MS commandline reg.exe to update the values. (the way I have it set is to have 2 copies of the registry data for the default profile)((exported straight from regedit)

my batch file runs as:

Code:

REG import C:\SPDIF_ON.REG
OR
REG import C:\SPDIF_OFF.REG

[fluffykeith]

Thanks for the info:

I think I understand.
Can you make the switch automatic when for example entering the video library in PVRX2? I guess not as you have it as a seperate command.

Sorry my question may not have been clear but you got it - basically I want stereo from the MP3 music and surround from everything else. Although I notice net radio now plays a bit odd (as in squeaky and pops) and I want that stereo.
The problem I have is that some mpeg, the recorded ones play surround - great, but ones ripped form VCD's just play stereo. Its that bit I want to fix. I'm not sure what type of audio it is.

[fluffykeith]

I think I'm learning a bit more.
VCDs use MPEG-1 with an audio stream fixed at 1 stereo or 2 mono channels.
Whereas the recordings and DVD are MPEG2, which contains I guess multichannel sound.

I'm not sure if ac3filter can distiquish between stereo from a MP3 source or stereo from an MPEG source.
There are a lot of buttons in the config and a lot of manuals to read!

Keith

[JonnyCam]

an MPEG2 file can contain multi-channel audio, but what capture card are you using?

If it's analogue, I doubt it would be anything but 2 channel.
Can you try and see if the VCD plays differently if you check / uncheck the MPEG audio passthrough option in AC3filter?

You can download utilities which will tell you what codecs are being used for the audio & video streams in your file, and that can tell you whether it's AC3 or not.

The suround you talk about, is that only through your amp then? Is it dolby digital?

Thanks

[fluffykeith]

Update - I've fixed it with AC3Filter - great program.

Basically on the SPDIF tab the default setting is to restrict the sample rate to 48kHz - when I checked the 44KHz everything came out surround encoded. Then on the system tak I unchecked the Use AC3 for PCM (basically what I think stereo comes out as but keep MPEG audio checked).
This way I get the music from MP3s as stereo - the recordings as surround and the VCD rips as surround.
The net radio is a different issue as the web stations are ok just the favourites seem messed up.

Edit - the surround is encoded by AC3filter as dolby digital 5.1 and decoded by the amp.
The capture card is a Nova-T - digital free view - so the encoding would be multi channel I think

It seems that ac3filter knows its an mpeg regardless of the sound encoding contained in it. Is that right - anyway it seems to work.

Thanks

Keith