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.
Decode MPEG2 PES streams.
Multichannel output support (Win2k/XP).
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.
Nothing is required, just register it. From command
line: x:\somedir\> regsvr32 ac3filter.ax
Ñommand file - install.bat. It will copy filter
to System32 catalog (System for Win9x) and register it.
Uninstall.
If registred from command line unregister it
from command line too: x:\somedir\> regsvr32 ac3filter.ax /u
Ñommand file - uninstall.bat.
It will unregister and delete filter from System32 catalog (System
for Win9x).
Filter save its settings in registry at [HKEY_CURRENT_USER\Software\AC3Filter],
to delete it 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):
Ñhannels - 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. (In future
I plan to route low frequeces from all channels to subwoofer).
* 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.
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 started 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.). For Win9x/WinNT use 2-channel
mode.
Change
speaker configuration 'in place' possible only in certain cases. First,
file playing must be stopped (not paused!). Second, all intermediate
audio filters must support dynamic reconfiguring (format change without
full graph rebuild). So if you cannot set output configuration here
you need to set it in Control Panel.
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 :).
Configuration advices
* General
Always check speaker setting in Control Panel: Control
Panel->Sounds and Multimedia->Audio->Sound Playback->Advanced->Speaker
Setup.
Use stereo output under Windows 9x.
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:
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
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).
For multichannel format reproduction according
to Microsoft recomendations (http://www.microsoft.com/hwdev/tech/audio/multichaudP.asp)
WAVE_FORMAT_EXTENSIBLE is used. In theory it may work in any Winodws
version. But I didn't make it work with Win98/SB Live! with more than
stereo. You can try, especially if you have other sound card. If anybody
know how to play multichannel audio under W9x/NT please let me know how.
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. If something wrong with this program
and you want to help with debug download debug version: http://xvalex.hotbox.ru/download/ac3filter_0_53b_debug.zip.
It is debug.reg file you need to import. Then open file that causes
the problem. It is c:\ac3filter.log file will be created. Please, send it 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.
This will help me a much in fixing this bug.
Changelog.
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).
