About Fraunhofer's IIS MPEG Layer-3 Audio Codec for MSACM - versions A/P

Jan 8, 2006 at 8:24 PM Thread Starter Post #1 of 6

jiiteepee

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Hi

On Fraunhofer's MPEG Layer-3 Audio Codec for MSACM Pro, there is a settings panel with quality setting for different kbps ...

fraunhmpeg32kn.jpg


What does all those 4 options mean for the quality? Which is the best option (supp. Stereo?)?

As suggested on window, I'd like to make me more familiar with their meaning.

Are there any other differences between versions Advanced (l3codeca.acm) and Pro (l3codecp.acm)?

jiitee
 
Jan 10, 2006 at 12:35 PM Post #3 of 6
I'm no expert on the matter, but I'm pretty sure Stereo is the best option. Joint Stereo modes take advantage of duplicate sound data on the left and right channels and can thus get a slightly smaller filesize. I don't think Joint Stereo modes are used very often anymore, the marginally smaller filesize doesn't outweigh the loss in quality.

I don't know what the various different modes of JointStereo are.
 
Jan 10, 2006 at 12:38 PM Post #4 of 6
Joint Stereo MS should result in the best SQ. Regular stereo has no better channel separation, and unnecessarily uses up bits that could be used to improve sound quality.
 
Jan 10, 2006 at 1:32 PM Post #6 of 6
Thanks for the replies.

Stopped being lazy and digged the web.

Found fopm mediarwins.com

Different stereo mode models in MP3

Question:

What's the difference between the various stereo modes in MP3?

Answer:

'Joint Stereo' modes take advantage of the similarities between the L+R channels.
This allows more bits to be used in other areas and in many cases this can give an overall gain in encoding quality.
Almost all encoders use joint stereo when encoding at 128 kbits.

Joint stereo has 2 submodes called IS and MS.
'Joint Stereo IS' destroys phase information and shouldnt be used for high-quality encoding.
'Joint Stereo MS' means Middle/Side and is OK for use in most encoding.

However, for some audio, Joint Stereo MS may create a 'flanging' or 'swishing' effect. In these cases it's better to use 'Stereo mode'.
This mode creates 2 independent channels for both left and right.
When stereo mode is used, you should also use a higher bitrate (160 or 192 kbits) - Stereo mode will allocate about half of this bitrate for each channel.

In summary, for most audio, Joint Stereo MS at 128 or 160 kbits should be fine.
If your audio is especially 'wide' and creates flange you should use 'Stereo' mode. You can change these modes in the Radium codec control panel.


Och samma på finska:

Joint stereo

MPEG-äänen stereomoodeja on useita ja tässä on niiden yhteenveto:

* Dual channel - Kummallekin kanavalle varataan saman verran kaistaa eli bittinopeus jaetaan kahtia.
* Stereo - Dynaamisemmalle äänisignaalille saatetaan antaa enemmän kaistaa, muuten sama kuin dual channel.
* Joint stereo(middle/side) - Kahdesta kanavasta muodostetaan summasignaali ja erotussignaali, joista summa on normaali mono kun taas erotus pitää sisällään stereoinformaation. Samaa menetelmää on käytetty FM-radion stereototeutuksessa. Erotussignaalille voidaan antaa vähemmän kaistaa, jolloin stereovaikutelma saattaa lievästi heikentyä mutta laatu säilyy hyvänä. Yleensä toteutuksessa yhdistetään myös joitakin taajuuskaistoja, joille korva on vähemmän herkkä.
* Joint stereo(intensity) - On käytännössä lähempänä monoa kuin stereosignaalia. Tuhoaa vaiheinformaation, joten mahdollinen Dolby Surround -koodaus ei säily.



jiitee


P.S.
A 'good' link in this subject. - http://harmsy.freeuk.com/mostync/.
eggosmile.gif



ADDED:

This information is copied from LAME 'help' ("Lame Ain't an MP3 Encoder")

Stereo mode

Joint-stereo is the default mode for stereo files with VBR when -V is more than 4 or fixed bitrates of 160kbs or less. At higher fixed bitrates or higher VBR settings, the default is stereo.

stereo
In this mode, the encoder makes no use of potentially existing correlations between the two input channels. It can, however, negotiate the bit demand between both channel, i.e. give one channel more bits if the other contains silence or needs less bits because of a lower complexity.

joint stereo
In this mode, the encoder will make use of a correlation between both channels. The signal will be matrixed into a sum ("mid"), computed by L+R, and difference ("side") signal, computed by L-R, and more bits are allocated to the mid channel.
This will effectively increase the bandwidth if the signal does not have too much stereo separation, thus giving a significant gain in encoding quality.

Using mid/side stereo inappropriately can result in audible compression artifacts. To much switching between mid/side and regular stereo can also sound bad. To determine when to switch to mid/side stereo, LAME uses a much more sophisticated algorithm than that described in the ISO documentation, and thus is safe to use in joint stereo mode.

forced joint stereo
This mode will force MS joint stereo on all frames. It's slightly faster than joint stereo, but it should be used only if you are sure that every frame of the input file has very little stereo separation.

dual channels
In this mode, the 2 channels will be totally indenpendently encoded. Each channel will have exactly half of the bitrate. This mode is designed for applications like dual languages encoding (ex: English in one channel and French in the other). Using this encoding mode for regular stereo files will result in a lower quality encoding.

mono
The input will be encoded as a mono signal. If it was a stereo signal, it will be downsampled to mono. The downmix is calculated as the sum of the left and right channel, attenuated by 6 dB.


jiitee
 

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