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Topic: how are these different? (Read 3010 times) previous topic - next topic
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how are these different?

just curious about these terms. i have a general idea and understand the similarities. but how are they different, or are they just fancy names for the same stuff? I have noticed these terms being used in context of the foll:-
joint stereo: mp3
intensity stereo: mp3PRO
lossy stereo coupling: Ogg Vorbis

thanx

how are these different?

Reply #1 –
Probably someone more knowledgeable will give you a better answer, but just in case:

Joint stereo and intensity stereo are certainly different. Intensity Stereo is more recent and it alllows better quality in very low bitrates (which is mp3PRO's focus).

Lossy stereo coupling is a broader term, meaning the exact channel separation isn't preserved. In vast majority of cases it should be better because it saves bitrate for more necessary things.

how are these different?

Reply #2 –
Quote
just curious about these terms. i have a general idea and understand the similarities. but how are they different, or are they just fancy names for the same stuff? I have noticed these terms being used in context of the foll:-
joint stereo: mp3
intensity stereo: mp3PRO
lossy stereo coupling: Ogg Vorbis

thanx

joint stereo

mp3pro uses SBR (instead of the "old" intensity stereo)

vorbis lossy stereo is similar to intensity stereo

how are these different?

Reply #3 –
Quote
joint stereo

mp3pro uses SBR (instead of the "old" intensity stereo)

vorbis lossy stereo is similar to intensity stereo

Those links are good, especially the first and the third one.
By reading the linked documents you can find out that MP3 and Ogg Vorbis use different names for similar techniques:

MP3:
Joint Stereo Coding with lossless (Mid/Side Stereo) and lossy (Intensity Stereo) parts

Vorbis:
Channel Coupling with lossless (Polar Mapping and/or Channel Interleaving) and lossy (Phase or Point Stereo) parts

It looks like Vorbis uses the more advanced methods.


Just for the records: the SBR technique as used in mp3PRO and AAC is not related to the topic of joint-stereo coding.

how are these different?

Reply #4 –
Ok,  "Joint Stereo" means that you can use some algorithms to code channel pairs more efficiently than coding separately.

MP3:

- Dual Mono

Coding of two channels completely independently, i.e. 128 kbps dual mono is nearly equal of coding two 64 kbps streams - there are no inter-channel processings in encoder

- Stereo

Coding of two channels without joint stereo algorithms, but with processing of channel pairs in the psymodel and using same bit reservoir for all channels

- Joint Stereo
 
MS (Mid / Side)

Or "loseless"  joint stereo (loseless if no quantization is used)  is used in most cases and it should always be enabled.

IS (Intensity Stereo)

IS destroys phase information as well as spectral make-up for higher frequencies, and only remembers so-called ILD (Interaural Level Difference) - or: difference in intensities between L and R channels.  Other parameters important for localisation of the source like ITD (Interaural Time Difference) or ICC (interchannel coherence) are not stored.  Because of this, IS is not always very good - but at very low bit rates it can save a lot of space



AAC:

Same as MP3, but coding mode can be selected for each frequency band, unlike in MP3 where selection could only be made on frame basis.  AAC also comes with more "joint stereo" coding methods:

- Channel Coupling

Similar to Intensity Stereo, but for multichannel

- SBR coupling mode

Similar to Intensity Stereo, but working in SBR (HE-AAC or aacPlus) domain - by using SBR QMF filterbank - little bit better than Intensity Stereo because of better T/F resolution

- Parametric Stereo (new - coming in 2004)

Extraction of stereo parameters like Intensity Stereo, but apart from ILD it also remembers IPD (interaural phase difference),  OPD (overall phase difference), ICC (interchannel coherence)  and has much better time/frequency resolution than IS, because it operates  in separate T/F mode from core-AAC encoder.