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Author Topic: Help With AC3 Playback  (Read 1564 times)

glynor

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Help With AC3 Playback
« on: October 18, 2006, 11:32:17 pm »

Alright... It's best to admit it when you need help, and I do.  Generally, I'm pretty good with setting up and configuring my video codecs, monitors, and display settings to give me good video quality and color accuracy....

Sound is another story entirely.  My "stereo" (2 channel upmixed by the soundcard drivers to 5.1) sound quality has usually been passable, but my AC3 reproduction is just terrible (and has been for a long time).  I usually just assumed that they were bad encodes or something, and blamed it on the files.  It's not.  It's my system, and I need help.

First, here's what happens.  I can't hear large portions of the soundtrack to videos (most importantly the dialog) when they use AC3 multi-channel sound.  I know the audio is there, because if I go into FFDSHOW's Audio Settings and manually crank up the "Voice" setting in the Mixer control to 250% I can then hear it, but it's still completely overpowered by the "music and ambient sounds" part of the audio.  This problem seems to vary a small bit depending on the source, but it it quite common (and happens quite commonly on my own DVD encodes).  If I switch the audio settings in FFDSHOW to 2 channel, and let Creative's CMSS 3D expand the sound, then I can hear the audio just fine (but of course not properly).  Again.... It's not just all quiet, but the "front left and right" channels seem to be completely out of proportion to the rest of the audio.

Here's what I have (at least the stuff I think is related):

  • Creative Audigy 2 (Standard Edition).  Analog outputs used.  WDM Driver version: 5.12.8.1164
  • Klipsch ProMedia Ultra 5.1 Speakers
  • FFDSHOW used for AC3 decoding.  I have:

       - Dolby decoder enabled
       - LFE Crossover enabled
       - Mixer enabled with various settings

I have found that the situation vastly improves if I uncheck 32 Bit Floating Point under Processing --> Allowed Sample rates.  Should I just leave that unchecked?  Is there anything else I should have enabled (or disabled)?  What does 32 bit Floating Point do?  What are the "best practices" for a setup similar to mine (without a fancy external DAC and using SPDIF outputs)?
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glynor

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Re: Help With AC3 Playback
« Reply #1 on: October 18, 2006, 11:55:58 pm »

I only really discovered it while actually typing that last post, but de-selecting the 32-bit Floating Point really does seem to have solved things.  I'd still really like to know what the "right" things are, and if there is anything I could do better.
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Alex B

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Re: Help With AC3 Playback
« Reply #2 on: October 19, 2006, 07:24:45 am »

I recall that 32-bit floating point was not working well when I tried it. Probably MC expects the PCM stream to be in an integer format.

However, this should matter only with audio files that are decoded by ffdshow. If I have understood correctly a decoded video soundtrack never routes through MC's audio engine before the final output stage.

In theory FP is the best format because it is stepless. Professional audio editing programs use FP internally and can also save files in FP for future editing.

The usual source files are not in FP format. In any case you should not be able to hear audible differences between a FP and an integer format. Just use what seems to work.
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