IPB

Welcome Guest ( Log In | Register )

 
Reply to this topicStart new topic
Multichannel audio quality
~*McoreD*~
post Nov 30 2003, 05:13
Post #1





Group: Members
Posts: 568
Joined: 10-July 03
From: Australia
Member No.: 7693



Hi there guys,

When I was suggesting 128kbps Windows Media Audio 9 Professional would be enough for "CD Quality" to convert an AC3 file (which is extracted from DVD), one of my friends said:

QUOTE
I don't think 128kbps is good enough for encoding 5.1 sound. Think about it. 128 / 6 is 21.3. That's 21.3 kbps for each channel. That's the equivalent of encoding stereo sound at 42 kbps. I really don't think that's enough. I would recommend 384kbps for 5.1 sound. That's more like 128kbps for stereo and will sound much better.


My question: Is it how it works?

If that's correct we will need 384kbps at least in order to deliver 64kbps for each channel.

Thank you,
McoreD


Edit: Thanks guys for all your replied. Always learning something new. smile.gif

This post has been edited by ~*McoreD*~: Dec 24 2003, 02:15
Go to the top of the page
+Quote Post
rjamorim
post Nov 30 2003, 13:21
Post #2


Rarewares admin


Group: Members
Posts: 7515
Joined: 30-September 01
From: Brazil
Member No.: 81



QUOTE (~*McoreD*~ @ Nov 30 2003, 02:13 AM)
My question: Is it how it works?

No. Your friend ignored the existance of Multichannel Decorrelation.

This encoding technique means that the encoder encodes the redundancy among the channels only once, since it's a waste of space encoding this information on each channel separately.

That means something like: if you encode a stereo stream at 128kbps, the encoder encodes one stream "alone" at 56kbps, the other at 56 too, and the redundancy between them at 16 (56+56+16=128), giving each channel an actual bitrate of 72 (56+16) and not 64. (I hope I made myself clear)

AAC supports this technique, and WMA Pro probably does as well. Ogg vorbis does support, but it isn't implemented in the encoder yet.

I think a bitrate around 256-320kbps would be better for good quality.

This post has been edited by rjamorim: Nov 30 2003, 13:25


--------------------
Get up-to-date binaries of Lame, AAC, Vorbis and much more at RareWares:
http://www.rarewares.org
Go to the top of the page
+Quote Post
JohnV
post Nov 30 2003, 14:11
Post #3





Group: Developer
Posts: 2797
Joined: 22-September 01
Member No.: 6



Also LFE (Low Frequency Effect) channel is the supporting bass effect channel which probably doesn't take lots of kbps at all.


--------------------
Juha Laaksonheimo
Go to the top of the page
+Quote Post
Latexxx
post Dec 2 2003, 16:31
Post #4


A/V Moderator


Group: Members
Posts: 858
Joined: 12-May 03
From: Finland
Member No.: 6557



Microsoft claims(http://www.microsoft.com/windows/windowsmedia/9series/codecs.aspx) that wma pro @ 192 - 256 would be similar to 384kbps ac3.
Go to the top of the page
+Quote Post
rjamorim
post Dec 2 2003, 16:34
Post #5


Rarewares admin


Group: Members
Posts: 7515
Joined: 30-September 01
From: Brazil
Member No.: 81



QUOTE (Latexxx @ Dec 2 2003, 01:31 PM)
Microsoft claims(http://www.microsoft.com/windows/windowsmedia/9series/codecs.aspx) that wma pro @ 192 - 256 would be similar to 384kbps ac3.

Microsoft also claims WMA std has the same quality of MP3 at half bitrate.


--------------------
Get up-to-date binaries of Lame, AAC, Vorbis and much more at RareWares:
http://www.rarewares.org
Go to the top of the page
+Quote Post
2Bdecided
post Dec 2 2003, 17:00
Post #6


ReplayGain developer


Group: Developer
Posts: 4945
Joined: 5-November 01
From: Yorkshire, UK
Member No.: 409



QUOTE (rjamorim @ Dec 2 2003, 03:34 PM)
QUOTE (Latexxx @ Dec 2 2003, 01:31 PM)
Microsoft claims(http://www.microsoft.com/windows/windowsmedia/9series/codecs.aspx) that wma pro @ 192 - 256 would be similar to 384kbps ac3.

Microsoft also claims WMA std has the same quality of MP3 at half bitrate.

Yes, but the former is more believable, if not proven (yet).

Cheers,
David.
Go to the top of the page
+Quote Post
Ivan Dimkovic
post Dec 2 2003, 17:18
Post #7


Nero MPEG4 developer


Group: Developer
Posts: 1466
Joined: 22-September 01
Member No.: 8



QUOTE
I don't think 128kbps is good enough for encoding 5.1 sound. Think about it. 128 / 6 is 21.3. That's 21.3 kbps for each channel. That's the equivalent of encoding stereo sound at 42 kbps. I really don't think that's enough. I would recommend 384kbps for 5.1 sound. That's more like 128kbps for stereo and will sound much better.


In 5.1 channel config you have following situation:

2 channel pairs (L, R and L', R')
1 single channel ( C )
1 bass, or, LFE channel

In a coding system which does not use so-called inter-channel "coupling" you can figure it out by:

bit rate = 2 x stereo bit rate for same quality + 1 mono bit rate for same q + X, where X is only few kb/s for LFE...

So, for, say AAC - to achieve quality of 128 kb/s, stereo:
2 x 128 + 64 + 1 Kb/s = ~ 320 kb/s very close to, actually 321

For MP3 you would need:
2 x 160 + 80 + x... = ~400 Kb/s for the same quality

For HE-AAC:
2 x 48 + 32 (because of coupling channels need less) = 128 Kb/s

For MP2:
2 x 256 + 128 = 640 Kb/s


Etc...

This post has been edited by Ivan Dimkovic: Dec 2 2003, 17:22
Go to the top of the page
+Quote Post
Latexxx
post Dec 2 2003, 20:37
Post #8


A/V Moderator


Group: Members
Posts: 858
Joined: 12-May 03
From: Finland
Member No.: 6557



QUOTE (rjamorim @ Dec 2 2003, 07:34 AM)
QUOTE (Latexxx @ Dec 2 2003, 01:31 PM)
Microsoft claims(http://www.microsoft.com/windows/windowsmedia/9series/codecs.aspx) that wma pro @ 192 - 256 would be similar to 384kbps ac3.

Microsoft also claims WMA std has the same quality of MP3 at half bitrate.

The page, which I am referring to, isn't ment to be read by some lamers who believe that xing mp3 is listenable at 96 kbps. Its target audience is most likely to be big-scale broadcasters and tv companies because it compares wm9 to mpeg2 at broadcast bitrates instead of saying something like "mpeg-4 quality at half bitrate".
This page might give even some correct information because most of their claims are believable even when thinking mpeg-4.
Go to the top of the page
+Quote Post

Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



RSS Lo-Fi Version Time is now: 20th April 2014 - 11:59