Frequency Distribution and Multichannel Systems

[Tuning]

This is a general question,but software and sound related.The frequency distributions of 5.1 or greater systems is the topic.That is for a 5.1 Speaker/Software system we have 3 front and 2 rear channels and a big box for 0.1 or LFE.We can hear the full spectrum some what through FL & FR channels,even though we have dedicated subwoofer for low frequencies.Through RL & RR channels only mid(above 2khz)-high range frequencies are produced and we can hardly hear low frequences.But on other hand some low frequencies are available in front channels(L & R).Some times the "C" channel only be having mid frequencies.
So the question is whether this frequency distribution is correct and is all of the 5.1 S/W & H/W (Sound Cards ) systems are following this.By Software system I mean the different sound technologies like Dolby Digital,DTS,SDDS,THX....etc and the software players capable of playing it.
If not, can anyone state how the actual frequency distribution is done in these commercial sound systems.Any other information that you would like to share?

Thanks.

-Tuning

[SomeJoe]

The specs you are quoting, where each channel of the system has certain frequency limits, is not true of the specifications for 5.1 discrete surround systems like Dolby Digital or DTS. Those specifications were more applicable to older surround sound systems like Dolby Pro Logic.

A Dolby Digital 5.1 audio stream may be authored assuming full range (20Hz - 20kHz) audio for FL, FR, C, RL, and RR. If the speakers attached to the audio system are not capable of this range of frequencies for each channel it is up to the receiver/processor to allocate frequencies as it sees fit. It is not the responsibility of the audio stream/AC3 author to compensate for sub-standard audio systems.

An example is as follows, and also illustrates proper use of the LFE channel: You have a section of audio for the production that uses all channels, and includes a heavy bass music track. The scene is shot in first-person, and the audio author wants it such that when the person in the film turns his head, the music he is listening to pans around the room accordingly.

This should be authored exactly like it sounds: The bass frequencies as well as all the other frequencies from the music should pan through the front, center, and rear channels as appropriate. None of the bass should intentionally be moved into the LFE channel. The LFE channel is reserved for those extra effects like explosions and crashes that need a little bit of extra emphasis. The LFE channel is not to be used as the "bass" channel.

Now, if the audio setup the consumer has is designed with bookshelf speakers for all 5 channels plus a subwoofer, the receiver/processor of that system is responsible for routing the low frequencies that occur in the other channels to the subwoofer. For a consumer that has a higher-end audio system with low frequency transducers (woofers) in all speakers, no bass re-routing will be required. A high-end system with woofers in all speakers may not need to even have a separate subwoofer, if the receiver/processor intelligently routes LFE content to the other speakers which are capable of reproducing low frequencies.

In short, the audio stream author need not worry about the consumer's speaker setup, as that is not his responsibility. As far as the audio author is concerned, the 5 directional channels can do 20Hz-20kHz, and LFE can do 120Hz and down.

This is how Dolby Digital is intended to work. I believe DTS is intended to work similarly, but I have not read the specs for it. For more information on bass management in general, see section 3.5 of Dolby Digital Professional Encoding Guidelines (http://www.dolby.com/tech/L.mn.0002.DDPEG1.pdf).

[vinouz]

The LFE is reduced to a central speaker just because We don't have much spatial separation for low frequencies (as for, in another side effect, for high frequencies). So it's in fact no much use to encode 5 complete dynamic channels, as we could encode all on the LFE and then add this LFE to all speakers if the audiophile system permits it. It would make no perceptual difference.
So, if the question was to think aboud using Garf's 4kbit/s vorbis mod for LFE and highpass the other channels before recode (for example, just for example, eheh ;) ), I suppose that wouldn't be a complete stupid idea at all.

[SomeJoe]

Originally posted by vinouz
The LFE is reduced to a central speaker just because We don't have much spatial separation for low frequencies (as for, in another side effect, for high frequencies). So it's in fact no much use to encode 5 complete dynamic channels, as we could encode all on the LFE and then add this LFE to all speakers if the audiophile system permits it. It would make no perceptual difference.

It is true that spatial separation for low frequencies is not required, and if the audio system is a 5.1 system that takes LFE into account, there would be little to no perceptual difference if all bass was in LFE, but this is not the proper way to mix DD audio.

For systems that downmix 5.1 Dolby Digital to Dolby Pro Logic or plain old 2-channel stereo, it is permissible for them to ignore LFE. Therefore, if the bass is supposed to be part of the standard track mix, it must be included in one or more of the 5 directional channels (usually FL and FR), not solely in LFE.

Again, LFE is reserved for those extra effects like explosions and crashes that need a little bit of extra emphasis. The LFE channel is not to be used as the "bass" channel. It is the responsibility of the receiver/processor to perform bass management based on the actual speaker setup.

[jorel]

Originally posted by SomeJoe
It is true that spatial separation for low frequencies is not required, and if the audio system is a 5.1 system that takes LFE into account, there would be little to no perceptual difference if all bass was in LFE, but this is not the proper way to mix DD audio.



not "a little",only the high harmonics from basses
are out of LFE(in 5.1),remember that for our ears
can hear more harmonics from basses than from trebles.
in 100hz we can listen "dozen" harmonics and in
6khz(for example)no more than 2 high harmonics.
and the "littles" surround speakers can't show the low basses
or they will "brake".....
only this high harmonics(2,4,..etc)can be in the "surround speakers.

..of course,forgive my poor english!
:)

[Tuning]

Thanks
SomeJoe,vinouz and jorel,

I got the point.I was in mood of bulding(Assembling) new Speakers for my system.I will take your opinion on frequency distribution for it.

Though I'm not building high-end audio phile system,It is goiing to be one as it has 4 set of full range speakers(Woofer+Midrange+Tweeter).
Oh! I forgot,I 'm using SBLive value 4.1 with no Subwoofwers.So will there be any listening difference if I use these full range speakers for all 4 Channels.[FR & FL,RR & RL]and as I already mentioned without subwoofers.

PS:Can anyone point me[link or explaination] to how the subwoofers are made and what type of speakers i need to use...
Thanks

-Tuning