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Rockbox mail archiveSubject: RE: Quick questionsRE: Quick questions
From: BlueChip <cs_bluechip_at_webtribe.net>
Date: Mon, 20 Oct 2003 21:10:38 +0100 >Hi BlueChip, > >I don't want to start a flame on the best stereo mode. No me neither, audio appreciation is entirely subjective. I hope I did not sound aggresive in my writing. If I did, I'm sorry, it was not intended that way :) >I was just interested if I had something wrong in mind (I didn't look it >up before I wrote my >message). Precisely what I did - posted what I "knew" and then read your contradiction - as I have no idea where my original "knowledge" came from, I just did a search and posted all the interesting stuff I found. > I will comment on your links in the following if you don't mind. Please do, I would certainly like to be corrected if I am wrong :) >BlueChip wrote: > > http://www.geocities.com/altbinariessoundsmusicclassical/vbr-e > > ncoding.htm#ch11 "Joint Stereo looks for signals that are identical > > in the left and right channel and if it finds any they are encoded as > > mono" > >I found that one, too. Sounds like a non-techie explanation of encoding sum >and difference to me. hmmm, maybe - not sure on that... > Signals that are really completely identical in the >left and right channel, even for the short time of a frame, don't exist >(except you copy one channel digitally) > > > with regard to the post on "you do not lose quality" > > === THIS IS NOT TRUE AT ALL === > > Whatever you may read from the net - I can personally assure you > > otherwise. And Yes, I HAVE been put through the "blind test" > > procedure by two of my friends now. ooohhhhh, that DID sound a little OTT didn't it - sorry, I was just covering my ar53. >What encoder did you use? I read that some commercial xing encoder had a >very poor joint stereo implementation in early times. Good question - these tests were carried out a couple of years back, when we (my peers and I) were all using Fraunhoffer. This is JUST "my opinion", there may be others that agree ...I don't know? I now use "LAME v3.93 -m s -b 160 -q 0" ...this gives me an acceptable compromise between quality and compression. Fraunhoffer is poor - the radium optimisations are 'allegedly' detrimental - I think I originally read that at mp3proclub. Xing is blindingly fast, and gives (imho) abysmal results > > http://www.mediatwins.com/FAQ/mp3_stereo_modes.htm > > "However, for some audio, Joint Stereo MS may create a 'flanging' or > > 'swishing' effect... > >Yes, I read this one, too. It says "for SOME audio...". Of course, if you >have extremely wide stereo signals or two mono signals, you gain nothing by >using joint stereo. LAME automatically switches to normal stereo in theese >cases, but they are very rare. In normal audio, you gain bandwith or quality >by using joint stereo. "Blue Oyster Cult - Don't Fear The Reaper" can give especially bad results, as ironically, did one of my own recordings. I suppose it was a few especially bad experiences, and all the flanging you get on downloaded filez, that just said to me "don't take the risk" so I just never use it any more. > > http://www.mp3machine.com/discussion/messages/780.shtml > > quotes William Schelter, Nils Faerber, Alexander Leidinger, Oct 13, > > 2001: "Using mid/side stereo [MS] inappropriately can result in audible > > compression artifacts. Too much switching between mid/side and regular > > stereo can also sound bad." > > ...which was given as a definition of Joint Stereo > >Again, I also found this site. It's not a definition of JS, it's just >describes the switching between JS and normal stereo with difficult signals. >The sentence which would come next in your citation is the real important >statement: >"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." :) Another mighty fine reason to use LAME ...but I did not want to make the presumption that everybody uses LAME, and also did not want to get into the "my compressor is better than yours" argument. > > http://www.iis.fraunhofer.de/amm/techinf/layer3/ > > "Joint stereo coding takes advantage of the fact that both channels of a > > stereo channel pair contain far the same information. These stereophonic > > irrelevancies and redundancies are exploited to reduce the total > > bitrate." ...whatever that means > >That's what I wrote. >If you have a normal stereo mp3 with 192kbps, you get 96kbps for each >channel. If you use joint stereo instead, you can use (I'm just guessing >numbers here) 160kbps for the mixed signal (sum of left and right). The >difference between left and right are very small, therefore 32kbps is enough >to encode it. The result is better quality for the main information. hmmmmmm, you've got me wondering now - me thinks it's time for some new experiments :) > > I cannot find defitions that agree with ANYTHING I have read so far, > > including my own post!!! > >The technique you were describing could work, but I think it's not what is >known as joint stereo. All surround systems use the fact that deep >frequencies can't be located easily and have only one subwoofer. However, >the threshold frequency for this effect is in the range under 200Hz, >therefore you'll practically gain nothing. Yes, it all made sense when I first posted - but I must say that everything you have written makes perfectly good sense. >Andreas Stemmer Hang Loose Andreas, BC Received on 2003-10-20 Page template was last modified "Tue Sep 7 00:00:02 2021" The Rockbox Crew -- Privacy Policy |