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Old 7th January 2004, 22:49   #7  |  Link
KpeX
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AC3 Playback Questions

7. Which software do I need to install for AC3 playback?

Download Valex's AC3filter audio filters and install. This filter is highly recommended over any other AC3 capable filter, it's very feature rich and best of all it's open source. Please read over his excellent documentation for a full understanding of all the capabilities of the AC3filter. Valex frequently updates the package so you might check Doom9's news or the AC3filter page often.

Secondly, you will need to use your favorite media player to playback the media container (ie. OGM, MKV, or AVI) which has the embedded the AC3 track.

[At this moment the AC3 codec is the most compatible with many devices, in the PC you only need a player like MPC-HC or VLC.
Maybe the question is how you have the conexion betwen the PC and your audio equipament, and what support that audio equipament:
- A modern AVR conected by HDMI: TrueHD/DTS-HD/EAC3/AC3/DTS passtrough, other formats decoded to PCM multichannel.
- A old AVR or only conected by SPDIF: DTS/AC3 passtrough, other formats downmixed to PCM 2.0 or recoded on the fly to AC3 with AC3Filter or similar.
- Only a analog stereo equipament: all formats must be decoded and downmixed by the player.

With LAV Filters or a correct player the rest of questions in this post are oldies.]

8. How do I determine if the filters are registered and installed correctly?

If the filter isn't installed correctly you'll typically see an error when playing back the media file such as “DirectShow can not render the file”. Open GraphEdit (can be found in Doom9's download section), select Graph>Insert Filters (Ctrl-F). A dialog should appear and you can double click the Direct Show category. This will display all DS filters that the system has registered and are available for use. Double click on a filter to see the path where the filter file resides on your drive (ie. C:\Program Files\AC3Filter\ac3filter.ax). If the filter doesn't show up in GraphEdit then most likely a problem with the install occurred and you should attempt an uninstall of the AC3filter and then reinstall using the supplied installer.

If the filter still isn't being loaded in your media player or GraphEdit then try manual registering. First verify where the filter physically resides by doing a search for ac3filter.ax, typically it will be in the path I note in the next line. Then open a DOS window prompt->type C:\Program Files\AC3Filter\. At this point we can now register the filter by typing regsvr32 ac3filter.ax, you should see a dialog pop-up indicating the filter registered properly. As an alternative you could try the Moonlight Odio Dekoda from Elecard here (has much less features than Valex's AC3filter but better than Intervideo)

9. Why don’t I hear any sound or the sound is garbled during playback?

Typically this problem is due to the way your system or media player is configured. The quick fix might be to check if your media player is using “DirectSound” or “WaveOut”. Most systems use “DirectSound” by default and will work fine but if you experience problems then try using “WaveOut” instead. Some users have also reported they have to use the Default Direct Sound device selected for proper playback (ie. Default Direct Sound Audigy). To switch DirectSound/WaveOut output, use the WaveOut fix package available on the Doom9 download page.

10. Why does the sound sometimes stop in the middle of my movie and then come back on?

Drop outs of audio over SPDIF can be caused by a poor quality power supply or you may need to purchase a surge protector to regulate current. Also, audio drop outs can be caused by a poor quality optical or coax cable. Some users have reported poor PC power supplies to be the cause as well. As a last thought, I have experienced drop outs if broken muxing tools such as NanDub was used with too tight of settings (ie. 64/64ms). More about muxing the AC3 follows below.

11. The AC3’s volume seems low during playback, what can I do?

Check your receiver manual to see if your amp supports DRC(Dynamic Range Control) which can increase the volume dynamically for AC3, thus making lighter sounds play louder and compressing the overall range.
Also, Valex’s AC3filter will allow you to manually adjust the master gain, DRC and has a built-in equalizer as well. If your passing the sound over SPDIF then the majority of the filters settings will have no effect in order to pass the AC3 stream to your amp properly. Remember, the AC3 packets can not be altered or your amp would not detect the stream properly. Valex’s filter of course complies with this requirement.

12. Does the muxing software and settings affect AC3 playback?

If you plan to pass the sound through SPDIF and use AVI then the answer here is clearly yes. Thanks to the great AVI muxing software (AVImux GUI) from alexnoe, perfectly smooth playback with AVI/AC3 can be achieved easily. AVImux GUI is highly recommended to mux AC3 into the AVI container. Until now we were pretty much limited to using NanDub for AVI muxing but recently it was discovered that the muxing code in NanDub is serious flawed. Therefore, it’s no longer advised to use NanDub for any type of muxing. Now that we have AVImux GUI, in general we no longer have to worry about the interleave values and just use the default 500/75 provided. Please read the forum threads and the AVImux documentation for more details. You can find the latest builds on alexnoe’s home page here or grab it from Doom9’s download section. If you're using CD media to play back from and the CD drive is being accessed excessively causing playback problems then you might want to try an AVI file using AVImux. AVImux will cut down on the CD drive access considerably thanks to the nice “rec-list” feature implemented. VirtualDubMod is also an excellent choice for AC3 in AVI muxing.

Additionally, using a modern container format such as OGM or Matroska will cut down on muxing problems, these formats generally have no problems muxing AC3. For matroska muxing try MKVmerge or for OGM muxing (OggMux_Nic).

[Use always MKV]

13. What effects might I see if the AC3 files have been muxed improperly?

The most common problem seen if broken muxing software (NanDub) was used is to have jerky pan & scan scenes during playback or audio stutters. Another common problem might be excessive CD drive activity as mentioned above. Watch a movie closely when the camera pans from left to right or vice versa, it should be very smooth. An easy way to compare is to watch your ripped AVI without any audio muxed and then watch the same clip after you have muxed the AC3, you should not see any difference in regards to smooth playback (ie. Pan & Scan scenes). One last common symptom of a poorly muxed file is to hear the audio stuttering or dropping out during play, especially during high action scenes.

14. Why doesn't WinAmp playback AC3 files properly?

WinAmp doesn't support AC3 files natively. Valex has once again come to our rescue and provided an excellent plugin though. The AC3 plugin can be found here.

15. How can I playback a Dolby Digital wav (ddwav) on my PC?

VideoLan's VLC player version 0.7.1 and up supports playback of DDWavs and Dolby Digital-CDs.

Alternatively, you could first extract the 5.1AC3 stream from the DD-WAV using BeSplit and then play it in any player that is capable of playing ac3. An example command line is:

BeSplit -core( -input live.wav -output e:\track01.ac3 -type ddwav -fix )

16. What troubleshooting can I do to fix S/PDIF playback?

If you're still having problems troubleshooting, you can render the file in GraphEdit to get an idea on which filters might be needed. In GE, select the File Menu->render media file>load GraphEdit, add a File Source (Async) DirectShow filter, select your AVI file and to render it (right click on Output / Render Pin) to see what happens. That's how you'll know if DirectShow isn't able to properly render the file.
It’s been reported that Cineplayer's audio filter provides better SPDIF playback compared to say Intervideo. Cineplayer’s filter is also reported to work with SoundBlaster Live 5.1 cards with little effort. Valex’s AC3 filter is still preferable due to it’s ease of use and many features. Disable or uninstall the Morgan Stream Switcher filter. This filter can cause playback problems (e.g. stutter/skipping). The filter name is mmswitch.ax. Try the following command in the directory where the file is located- regsvr32 /u mmswitch.ax

If you're running Windows 2000, make sure you have at least Service Pack 2 and the latest sound card drivers are installed. SP2 solves some SPDIF out issues.

DirectX 8.1 and up is highly recommended. WinXP should have 8.1 already installed.

17. Any tips for Soundblaster sound cards?

The original Live Value(CT4780) cards requires a “stereo” 3.5mm mini plug and the newer models require a "mono” cable. If your sound card has an optical/Toslink or coax port, this will provide the most optimal quality, this compared to the multi channel analog ports. It’s possible that the coax can get interference known as EMI, although this is very rare.

On the SoundBlaster Live card software, make sure “Bypass SPDIF” option is _not_ checked.

Windows 9x/ME: In the SB mixer, check "digital out only". Also, uncheck "decoded AC3" and uncheck "bass redirection". Start your favorite media player and select SPDIF out in the audio configuration.

Windows 2000: At least install service pack 2 or later. Install SoundBlaster drivers v3512. In the SB mixer, check "digital out only". Also, uncheck "decode AC3" and uncheck "bass redirection” Start your favorite media player and select SPDIF out in the audio configuration.

Windows XP: This OS should not require any tweaking, driver shuffles or service packs for proper playback and SPDIF setup.

The Creative LiveWare software 5.1 sound test will not work for all 6 channels. It’s best to test your connection with a Dolby Digital 5.1 DVD if possible.

If you currently own a SoundBlaster 5.1 or a Live! model and are using SPDIF, your advised to buy the Hoontech adapter which allows correct voltage out for SPDIF. Link- (Important when using an IDE cable: The colored side of the cable should be on pin 1 on both Hoontech and
SoundBlaster card!)

Also, see the Creative FAQ for the 5.1 sound cards- http://www.soundblaster.com/support/...ily=1#faqstart

Creative’s Audigy can not decode DTS but it can pass it via SPDIF. The card can pass both DD and DTS as well as decode Dolby Digital also. It was pointed out by Goa333 that it might be a good idea to do a listening test between your AC3 decoding options such as WinDVD, PowerDVD, Sound Blaster AC3 hardware decoding and of course an external AC3 decoder. Your quality might be much better using one or the other. It has been reported that the Audigy card might suffer with AV sync problems using Wave Out as the audio device. Instead of setting this to “Wave Out” within the software player, it’s possible "DirectSound SBAudigy Wave Device" might solve sync problems if experienced.

18. What sound cards are most recommended for S/PDIF playback?

Audio Excel-Theater Excel-$19 USD
Hercules Fortissimo I & II-$45 USD
Hercules Game Theater XP- $95 USD
Turtle Beach Santa Cruz- $60 USD
Terratec DMX XFire 1024-$58 USD
Philips Acoustic Edge - $55 USD
M-Audio Audiophile 24/96 - $??(Highly recommended for Audiophiles)

Any C-Media 8738 based sound card has given great results whether it’s built-in to the motherboard or a PCI card. These cards are low budget but perfect for an inexpensive SPDIF setup. They also pass both DTS and DD without issue. Here are a few cards with the chipset-

AudioExcel MD-Mate - $??
Yamaha X-Wave 7000 Pro - $??
Zoltrix Nightingale Pro 6 - $35 USD

Philips Acoustic Edge is reported to work very well in VIA motherboards, perhaps more so than other cards. It’s advised the sound card be installed to the farthest PCI slot from the CPU.

As a last thought, the nForce and nForce2 motherboards seem to be perfect for Home Theater use

Note: All Creative cards are purposely not listed above due to the ongoing hardware/software issues on most of the models. Issues range from bad drivers, jitter, SNR to out of voltage specifications which could damage your external amp. The intent was to show cost effective sound cards which are easy to configure for multi-channel and SPDIF playback.

[Now all PC's have HDMI or SPDIF output without need specific sound card. That info is outdated]

19. Any AC3/spdif information for linux?

All the popular players for linux (xine, mplayer, vlc) include AC3 decoding support 'out of the box'. For s/pdif output, your player will need must also be ALSA (advanced linux sound architecture) compatible. Steps to using alsa are as follows:

1. Make sure your sound card is supported by checking alsa-project.org.

2. Make sure your kernel has alsa support compiled in. ALSA is the default sound architecture in the 2.6.x kernels, and many 2.4 kernels shipping with distributions are compiled with alsa built-in.

3. Install software & set up your soundcard: make sure you have the alsa-driver, alsa-lib and alsa-utils installed (may be called something else in different distributions) and run alsaconf. You will be prompted to select your soundcard. If you have no error messages, then run alsasmixer to set your default levels. Make sure to activate the S/PDIF output if you wish to use it. On my card, this is referred to as "IEC958 output".

4. Install a player with alsa support. The simplest way to see if mplayer has alsa support is to type 'mplayer -ao help' and see if alsa is one of the choices. If your mplayer does not contain alsa support, simply build mplayer from source, and if you have alsa-lib (+ alsa-lib-devel on some platforms) mplayer will detect and compile in alsa audio out support. Then add a '-ao alsa' to your playback command or your mplayer.conf file, and the alsa output will be used. To playback AC3 over spdif, you'll also need to add a '-ac=hwac3' switch to your commandline. Alternatively you can add 'ac=hwac3,' to your mplayer.conf file (note the comma after hwac3), which will cause mplayer to try ac3 pass through first on any file and then other codecs.

(http://www.linuxdvb.tv/documentation/ac3sound.html)
(http://www.au.linuxvideo.org/)
http://liba52.sourceforge.net/

20. Is it possible to record AC3 via SPDIF in?

Yes. For a guide and discussion, see this post and the comments that follow.

Last edited by tebasuna51; 27th September 2021 at 11:45. Reason: update
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