AC3Filter ver 0.55b

Russian version

Download: server1 sourceforge

AC3Filter - it is DirectShow filter for AC3 decoding. Playing .AVI with AC3 audio tracks and MPEG2 (DVD). Distributed absolutely for free (FREEWARE). Sorry if my English is bad, but I think it is better to have something than nothing.

Main features:

Full AC3 standart compliance.
S/P DIF support (experimental).
Decode MPEG2 PES streams.
Multichannel output support.
LFE support.
Dynamic Range Compression (DRC) support.
Overflow control and automatic gain control.
Gain levels control.
Bitstream information (channel format, bitrate, sample rate, coupling freq and maximun freq).
Input/output levels.
Matrix mixer with direct control of mixing matrix.
Stereo to multichannel mixing.

Download.
Install.
Uninstall.
Usage.

Main settings
Mixer settings

Setup

Speaker configuration

Windows 98

Configuration advices
Registry

Misc
Distribution.
Contact author
Changelog.
Useful links.

Download.

Install.

Сommand file - install.bat.

To install from command line run:
x:\somedir\> regsvr32 ac3filter.ax
Then import presets file preset.reg.

After install you may need to set speaker configuration (look at Speaker configuration).

If you are using Windows 98 Simplified Chineese and filter's property dialog is too small you can try dialog_patch.exe patch (run it again to revert changes).

Uninstall.

Сommand file - uninstall.bat.

To install from command line run:
x:\somedir\> regsvr32 ac3filter.ax /u
If you want to remove all settings from registry then import uninstall.reg file.

Usage.

Filter decode ac3 streams from .avi and mpeg2 files. If everything is good then when file is open filter must be in application filter list. For Windows Media Player 6.4 filter list is at File->Properties->Advanced:

First in this example is ac3filter itself. If we open properties we'll see:

Main settings

* Bitstream information.

Top left it is bitstream information (BSI):

Сhannels - channels configuration in form front_channels/surround_channels + LFE (Low frequency effects channel) presence flag. In this example it is 3 front, 2 surround and LFE channels, i.e. 5.1 configuration.
Sample rate [kHz]
Bitrate [bps]
Freq (coupl/high) - [kHz], coupling frequency and high freuency. In ac3 some channels (in most cases all channels) are grouped in one coupling channel beginning from some frequency - coupling frequency and stored in the bitstream in that form. So channels are really independent only in some frequency band - up to coupling frequency. High frequency is a maximum frequency coded, so it defines total frequency bandwidth.
Frames/errors - total number of decoded frames and number of errors when decoding.

* Speaker configuration switch.

Left bottom it is an output speaker configuration switch. It define the real speaker configuration to wich ac3 channels will be mixed. Checkbox Subwoofer define presence of independent subwoofer (.1 channel). When present LFE is routed there, else LFE is routed to all other channels.

'SPDIF' checkbox means that ac3 stream will be routed to digital out of sound card directly and without any modification. So no one of other settings will work if this checkbox is checked.

It is nessesary to note that speacker configuration from filter properties can be changed only in certain cases. First of all playing must be stopped before (not paused). But in some cases speaker configuration cannot be changed at all (look at Speaker configuration).

* Gain levels.

Buttom middle it is gain level controls.

Master - desired gain level.
Gain - shows current gain level.
LFE - LFE channel gain level
Voice - center channel gain level (dialogue channel)
Surround - surround channel(s) gain level..
BSI Lock checkboxes - lock channel gain level at values given by standart. You cannot change Voice, LFE and surround gains when it is enables.
Normalize - one-pass sound normalize. (look at Mixer settings)

Master and Gain controls are responsible for global gain level. Master sets desired gain level. If current sound level is too high and overflow occurs then real gain level will decrease. Current gain level shown at Gain control.

* Dynamic range compression.

By its nature ac3 is a logarithmic format. Samples are stored in form of exponents and mantissas. In terms of bits one sample can be up to 40bits long (only theoretically) or up to 24bits (normal). It provide huge dynamic range (but, as said by great Einstein all good things in this word are relative :-). This means that quiet sound with low level when played on 16-bit sound card will be not audible at all or will have very low absolute level (=> high distortions). To solve this problem it is dynamic range comression. Main idea is to raise level when sound is quiet (and vice versa when loud) before converting to 16-bit form. There are special markers in ac3 stream for current level change. This markers are set by producer at a mastering stage, so it guarantees high quality. DRC level indicates this level. With 'Use DRC' chekbox you can enabe/disable using DRC. (of course this is only rough problem description).

DRC Power control adjusts how much DRC level changes sound level. When DRC Power is increased all quiet sounds will be more stressed and loud sound will be more shaded. When decrease DRC Power dynamic range compression will have less influence at output. Zero DRC Power level means that dynamic range compression applied at normal.

* CPU load.

Indicates CPU load by sound decoding and processing. All sound processing (if exists) before reproduction included here.

* Input/output levels.

Right part - levels indication. Note that levels here are in logarithmic scale. Input levels shows real channels configuration. Often happens that when BSI shows 5.1 in real LFE channel is absent.

* Presets

Combo box at bottom right allows to load predefined sets of settings (presets):

standart - maximum standart compatibility
one-pass normalize - as named, for maximum loudness.
LFE boost - LFE boosted at +10dB.

Mixer settings

Second page is mixer settings.

Main control here is mixing matrix. It is in form of matrix multiplication: S' = M S, where S = { L, C, R, SL, SR, LFE } - input sample, S' = { L', C', R', SL', SR', LFE' } - output sample.

For convenience some controls from Main page are placed here. For its description look at Main settings.

Settings description:

Auto matrix - automatic calculation of mixer matrix. When this option is enabled direct edit of mixing matrix is disabled. Gain levels LFE, Voice and Surround are parameters for matrix calculation. When this option is disabled next controls loose influence: Gain levels LFE, Voice and Surround, Normalize matrix, Expand stereo, Voice control. Following controls are remain to work: Master, Gain, DRC level, DRC power, One-pass norm. Direct matrix edit is enabled.
Normalize marix - matrix normalization. When this option is enabled matrix is normalized so it is no overflow at output (sum of channels at output < 1). But when gain level LFE, Voice or Surround changes other chanel gain level will be also changed (for example if we increase level of LFE other channels level will be decreased). Disable of this option allows to avoid this effect. But overflow is possible in this case. So you'd better to decrease Master gain when this option is disabled.
One-pass norm - one-pass sound normalization. When this option is enabled autoatic gain control works this way. When overflow occur it decrease current gain proportionate to overflow level (so it si no overflow at output) and gain level remains at this state until next overflow. Master is starting gain level. When this option is disabled current gain is always changing towards Master gain. So after overflow current gain will increase bit by bit until it reaches Master or other overflow occur. This mode is used when no overflow is expected. But if it is happen nevertheless gain will be restored after some time.
Expand stereo - works only when input mode is stereo. Allows to amplify out-of phase signal components. It works as surround sound amplification but not the sounds in center (dialogues are not amplified). Surround control works as amplification level. If rear speakers are present at output this out-of phase components routed there.
Voice control - works only when input mode is stereo. Allows to amplify in-of phase signal components. It works as center amplification (dialogues). Voice control works as apmplifiction level. If center speaker is present at output central component routed there.

Combo-box allows to save and load saved matrices.

Setup.

Speaker configuration.

When first run filter checks for current speaker configuration for downmix. It uses settings from Control Panel->Sounds and Multimedia->Audio->Sound Playback->Advanced->Speaker Setup. (For SB Live! users. When change speaker configuration from Surround Mixer it is not always change in Control Panel. So it is always good to check there.).

Current speaker configuration is always saved in registry when filter unloads. So after first start speaker configuration is independent from ControlPanel settings.

To change speaker configuration you can use ac3speakers.exe program:

Program changes speaker configuration in _deafult preset which is loaded when filter loads (look also Registry). Autodetect means that speaker configuration will be readed from Control Panel (see above).

To reset current configuratin you also can import reset.reg file (look at Registry).

You can change speaker configuration from filter properties only in certain cases. First of all playing must be stopped before (not paused). Second, all intermediate audio filters must support dynamic reconfiguring (format change without full graph rebuild).

In most cases problems are because of mmswitch filter (filter that support .avi (and DVDs too) with several audio tracks and allow to switch between, especially for multi-language films). If you mainly watch DVDs it is better to uninstall this filter and use MPEG2 parser wich support stream switching directly (standart MPEG2 Splitter for example). In this case you'll also get lower CPU usage. If MPEG2 parser does not support stream switching (Elecard for example) then many audio rendering chains created, all of them are working together when only one really reproducing.

If mmswitch is really needed then it is several possibilities:

All audio streams are ac3. mmswitch may be used in any speaker configuration. Speaker switch 'on place' will not work. So you'll need to set it before playing.
First stream is ac3, and second is mp3 (just for example, may be any non-multichannel format (stereo or mono)). If ac3 is needed then everything is ok. You'll need only to set desired speaker configuration in Control Panel before playing because of online switch will not be available. If you'll try to switch to mp3 you'll get bad sound because audio with only stereo channels will be played as audio having quadro (for example) channels. So if you want to play mp3 track you'll need to set stereo speakers in Control Panel.
First stream is mp3 and second is ac3. In this case it is only stereo playing possinble. Do not forget to set it before playing!
No ac3 streams - no problem :).

Windows 98

Only stereo configuratin supported by default in Windows 98 (and no spdif also). Support of this modes is at experimental stage now so it may not work on some systems.

First you need is install microsoft patch for WaveOut:
http://xvalex.hotbox.ru/download/269601usa8.exe

Second is set WaveOut Device as default device for audio output. In some players you can configure it but in most you cannot. So in most cases you need to explicitly set WaveOut Device as default sound renderer. You can do it with set_waveout.bat comamnd file (set_directsound.bat command file set back DirectSound as default renderer).

After it in most players multichannel modes and spdif output may work. Speaker configuration you have to set before (it will not work in filter properties).

Configuration advices

* General

Always check speaker setting.
Use stereo output under Windows 9x if other modes do not work.
When downmix from 2/2 or 3/2 to stereo it is safe to increase a little Master gain level, since level af rear channels is usually lower then front channels level.
Too loud transltor voice level can be lowered with Voice control. If it is stereo sound track then Voice control needs to be enabled.
Dolby recommends increase LFE mixing level up to 10dB. But in this case other channel level is decreased (when Normalize matrix option is enabled) or overflow possible (when Normalize matrix option is disabled).

* Maximum standart compatibility

Master = 0dB
DRC Power = 0dB
BSI lock = all on.
Auto matrix = on.
Normalize matrix = on.
One-pass norm = off.
Expand stereo = off.
Voice control = off.

Recommended in all cases.

* One-pass normalization.

Master = +10..+20dB
One-pass norm = on.

To play at maximum loudness.

Registry.

Filter saves its state in registry key: [HKEY_CURRENT_USER\Software\AC3Filter]. 'preset' key contain different keys for each set of settings (preset). When filter is loading '_deafult' preset is always loaded, when filter is unloading all settings are saved there. Registry values:

acmod (int) - speaker configuration, set on preset load. This value may be absent. In this case speaker configuration will not be changed on preset load.
matrix (text) - name of mixing matrix to set on preset load. Make no sence when auto_matrix option is set. This value may be absent. In this casae mixing matrix will not be changed on preset load.
master (double) - main gain level
clev (double) - central channel gain level
slev (double) - surround level gain level
lfelev (double) - LFE channel gain level
clev_lock (bool) - central gain level lock
slev_lock (bool) - surround gain level lock
lfelev_lock (bool) - LFE channel gain level lock
dynrng (bool) - use dynamic range compression
dynrng_power (double) - dynamic range compression power
auto_matrix (bool) - use automatic matrix calculation
normalize_matrix (bool) - normalize mixing matrix
expand_stereo (bool) - extract surround from stero input
voice_control (bool) - extract center from stereo signal

acmod value meaning:

Value	Speakers
0	2/0 (stereo)
1	1/0 (mono)
2	2/0 (stereo)
3	3/0
4	2/1
5	3/1
6	2/2 (quadro)
7	3/2

Add 8 to this value to indicate LFE channel. So in 5.1 mode acmod is 15 (7+8). To indicate SPDIF add 32 to acmod. Value 64 and more mean non-existing mode and interpreted as autodetect.

Mixing matrices are stored in 'matrix' key. Each sub-key contains only one matrix. When filter is loading '_default' matrix is always loaded, when filter is unloading current matrix is saved there. Matrix values called next way: [from_channel]_[to_channel], where from_channel is mixed to to_channel with factor given in value.

All levels are stored in factor form (not dB).

To reset all settings to default import reset.reg file. This will delete '_default' preset and '_default' matrix.

Misc.

I want to say thanks to Marcello Mota for support and big help in hard work of debugging and testing.

Filter was primarily based on Open Source LibA/52 library (http://liba52.sourceforge.net) and mainly inherits its characteristics. Much was rewritten but I tried to keep its merits. I want to note high quality of this lib and high compliance with standart (http://www.atsc.org/standards/a_52a.pdf).

Distribution.

This program distributed under GNU General Public Licence v2, placed in GNU_eng.txt at english language and GNU_rus.txt at russian language. Russain language version is only for information purpose only and english version have priority with all variant reading.

This application may solely be used for demonstration and educational purposes. Any other use may be prohibited by law in some coutries. The author has no liability regarding this application whatsoever. This application may be distributed freely unless prohibited by law.

This product distributed in hope it may be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose and compliance with any standarts. I do not guarantee 24-hour (and any) support, bug correction, repair of lost data, I am not responsible for broken hardware and lost working time. I am not responsible for legality of reproducted with this program multimedia production.

Contact author.

With all questions about this program please, email to this address. Please, respond about all errors in porgram with following information:

Problem description
Windows version
Sound card
Speaker configuration used (stereo, quadro, 5.1...).
If filter's property page can be opened then data from 'bitstream information'.
If you know what Graphedit is, then also screenshot (or just description) of graph caused problem.
If problem connected with incorrect sound then send a part of ac3 stream caused problem.

This will help me a much in bug fixing.

Changelog.

0.55b - 25.11.2002
+ Bug fixed: surround and voice gain controls did not work in 5 channel mode
+ Bug with decoding stereo files fixed

0.54b - 01.10.2002
+ SPDIF pass-through output.
+ Preset loading and several standart presets added.
* Speaker configuration is now saved to registry.
+ Speaker configuration program added.
+ Patch for dialog size in Win98 Chieneese
+ Bug filxed - in some cases filter settings was not saved.

0.53b - 14.09.2002
! Filter is distributed under GPL lisence now.
+ save settings to registy.
+ mixer control page with mixer matrix added.
* LFE channel is now mixed only to front speakers.
* 'Normalize' checkbox on main page means now one-pass normalization.

0.52b - 01.09.2002

+ Bug fixed - hang on corrupted PES streams.
+ Sound volume increased.
+ Overflow control and automatic gain control added.
+ Master gain control added.
+ DRC power control added.

0.51b - 18.07.2002

+ Bug fixed (crash on some ac3 formats)

0.5a - 07.07.2002

* AC3 decoder code was fully rewritten
+ PES support added.
+ Levels for LFE, Surround and Voice locked to BSI by default.
+ CPU usage indicator
+ Input and output levels inidicators.
+ DRC level indicator.
+ Some information about stream added.
+ Some bug fixes.

0.4a - 23.06.2002

+ LFE support and LFE gain added.
+ Added buttons for reset all gains to BSI values.
+ Stereo now transmitted in standart format, so now filter can work
with sustems with no multi-channel support (Win9x/WinNT).
+ DVD decoding added.
+ Syncronization problem fixed.
+ Option to enable/disable dynamic range compression added.

0.3a - 03.04.2002

+ Volume gain for central (voice) and surround channels.
+ Speaker configuration change support added. Only works when
all intermediate filters support dynamic reconfiguring and only
in stopped (not paused!) state.

0.2a - 01.04.2002

* LibA52 code was rewritten for multitasing, so now possible to
create many instances of the filter in a filtergraph. It is primary
used for multi-language films.
+ Information panel added (but settings are not working now).

0.1a - first working alfa

Useful links

AC3Filter site (rus+eng): (http://xvalex.hotbox.ru/programs/ac3filter)
AC3Filter site (rus+eng): (http://ac3filter.sourceforge.net)

A/52a standart (AC3) (eng): (http://www.atsc.org/standards/a_52a.pdf).
LibA52 library (was ac3dec) (eng): (http://liba52.sourceforge.net).
Multichannel audio reproduction at Windows (eng): (http://www.microsoft.com/hwdev/tech/audio/multichaudP.asp).
Just useful video-related site (eng): (http://www.doom9.org).
And one more (rus): (http://freetime.sinor.ru/observatory/digitalvideo).

Last updated 25.11.2002