Doom9's Forum - View Single Post - GUIDE: How To Properly Encode Dolby Digital Audio (AC3)

tbrunner · 14th November 2003, 22:29

Hi

I have also a lot of problems with bad AC3 sound resulting in to low volume dialogue (very difficult to understand) and to loud sound (explosions, music and so on).

My scenario is the following: I take a divx/xvid avi file and encode it to mpeg2 with AC3 sound to burn it on a dvd and watch it on a stand alone dvd player. I prefer AC3 sound as it is supported both for NTSC and PAL dvd's. As I would like to have the highest possible bitrate for the video, I encode the sound to two channel stero with 192 KB.

The sound in this divx/xvid files is either
a) MPEG Layer 1/MPEG Layer 2/MP3 or
b) AC3 5.1 or
c) AC3 2/0

My way of processing is:

1) convert the sound to WAV: For this I use the MPEG2 Encoder (Mainconcept in my case) to produce elementary video and audio streams. For the audio stream I select wav format. As the Mainconcept encoder uses direct show to read the file, AC3 Filter can be used to decode the AC3 sound and downmix it to 2 channel. I assume this works with every encoder who supports either direct show directly or can read avisynth files.

2) convert the WAV to AC3 using AC3 machine (I do not use AC3 Machine to downmix AC3 5.1 sound directly to two channels as proposed in the DOOM9 guide, because as result, I still get a 5.1 AC3. This surprises me not as the resulting command line is the same regardless if channels mode 5.1 or stero is selected).

Now my question is, where and what do I set to archive the proper 5.1 downmix to 2 channels, Dialog Normalization and Dynamic Range Compression. I would like to use as much as possible freeware tools.

I assume that the solution depends on the sound type in the avi.

a) MPEG Layer 1/MPEG Layer 2/MP3 (I assume that the low volume problem also occurs with this sound types as the people are not properly encoding the input AC3).
How and with what tool do I have to reencode the WAV to a WAV so that if feeding the WAV to AC3 Machine the sound is correct in the resulting AC3?

b) AC3 5.1
As the AC3 Filter provides so many settings, I assume that it is feasible to create a WAV file that can just be feed to AC3 Machine and the resulting AC3 sound is correct. The most obvious setting is to choose 2/0 stereo as output. To what do I set the other settings.

c) AC3 2/0
Some as AC3 5.1 but with different settings in AC3 filter.

Can someone give advice on the correct settings?

14th November 2003, 22:29	#27 \| Link
tbrunner Registered User Join Date: Jan 2003 Posts: 14	Hi I have also a lot of problems with bad AC3 sound resulting in to low volume dialogue (very difficult to understand) and to loud sound (explosions, music and so on). My scenario is the following: I take a divx/xvid avi file and encode it to mpeg2 with AC3 sound to burn it on a dvd and watch it on a stand alone dvd player. I prefer AC3 sound as it is supported both for NTSC and PAL dvd's. As I would like to have the highest possible bitrate for the video, I encode the sound to two channel stero with 192 KB. The sound in this divx/xvid files is either a) MPEG Layer 1/MPEG Layer 2/MP3 or b) AC3 5.1 or c) AC3 2/0 My way of processing is: 1) convert the sound to WAV: For this I use the MPEG2 Encoder (Mainconcept in my case) to produce elementary video and audio streams. For the audio stream I select wav format. As the Mainconcept encoder uses direct show to read the file, AC3 Filter can be used to decode the AC3 sound and downmix it to 2 channel. I assume this works with every encoder who supports either direct show directly or can read avisynth files. 2) convert the WAV to AC3 using AC3 machine (I do not use AC3 Machine to downmix AC3 5.1 sound directly to two channels as proposed in the DOOM9 guide, because as result, I still get a 5.1 AC3. This surprises me not as the resulting command line is the same regardless if channels mode 5.1 or stero is selected). Now my question is, where and what do I set to archive the proper 5.1 downmix to 2 channels, Dialog Normalization and Dynamic Range Compression. I would like to use as much as possible freeware tools. I assume that the solution depends on the sound type in the avi. a) MPEG Layer 1/MPEG Layer 2/MP3 (I assume that the low volume problem also occurs with this sound types as the people are not properly encoding the input AC3). How and with what tool do I have to reencode the WAV to a WAV so that if feeding the WAV to AC3 Machine the sound is correct in the resulting AC3? b) AC3 5.1 As the AC3 Filter provides so many settings, I assume that it is feasible to create a WAV file that can just be feed to AC3 Machine and the resulting AC3 sound is correct. The most obvious setting is to choose 2/0 stereo as output. To what do I set the other settings. c) AC3 2/0 Some as AC3 5.1 but with different settings in AC3 filter. Can someone give advice on the correct settings?