-q 5,99 and -q6,00

2004-07-02 19:35:47

Here is my situation: before aoTuVb2 released I used GT3b1. 192 kbs is my choice so I used GT3b1 at q5. After aoTuVb2 released and became recommended version I switched to it with q6. As I know Ogg Vorbis uses two stereo modes. One for q >= 6 and another one for q<6.  So I have encodings with two different stereo modes. If not to speak about Ogg Vorbis inside processes, do I have to bother about wich stereo mode is used? Does q5,99 and q6 have big difference in stereo image? What's the difference between them?
And one more thing. Ogg Vorbis HAS quality managment mode which we all use. If MegaMix will be at (aprox) q5,25 (nominal bitrate=188) as good as aoTuVb2 at q6 (nominal bitrate=192) why not to move q'6' on 188  ('6' is at 212 now).
I hope Ogg Vorbis will evolute. And every time nominal bitrate scale will be messed.  Imagine a newbie user always use q6. And gets sometime 212 and sometime 192 :-O. I think this is wrong.

Just an example

1. Bitrate                     
2. MegaMix scale
3. aoTuvb2 scale
4. my proposition for MegaMix scale 

1. 128------160-----180-----192-----212-----224
2. -4-------------------5------------------6----------
3. -4----------5------------------6-----------------7--
4. -4-------5-----------------6----------------7-------

IMHO IMHO IMHO

P.S. Of course proposed scale must be defined through comparative tests done between aoTuVb2 and pretender.

-q 5,99 and -q6,00

Reply #1 – 2004-07-07 00:45:02

Well since Megamix has GT3 tunings in it from -q5 (well 4 but not in full until 5) it has a higher nominal bitrate and more spikes to solve the problems with Vorbis.  It's just the way the GT3 tunings are designed.  As far as I know it would probably take modifying or dropping the GT3 tunings from the Megamix to achieve this.  I could be wrong though.

-q 5,99 and -q6,00

Reply #2 – 2004-07-07 01:00:43

First thing about stereo image is that, in my opinion, there would be hardly any noticeable difference in stereo image between -q 5.99 and -q 6.  Even though at -q 6, lossy point stereo is switched off, we must remember that even below -q 6, it is only ever switched on based on thresholds and operates in certain frequency bands.  The lower the bitrate you go, the more likely that point stereo will be used in more frequency bands I think.  So -q 5.99 should be quite safe I think.

Megamix was just an experimental merging that I did "on the trott", to see how much benefit we get from a quick merge.  At the time, I just merged in all the values from GT3b2 that didn't conflict much with aoTuV beta 2, and that included the changes in nominal bitrate (ie. 180 kbps at q 5).  Frankly, I was not aware that the merge, in some instances, would give lower bitrates than GT3b2 due to the inner workings of aoTuV, and with hindsight, perhaps it was not good idea to raise the nominal bitrates just yet.

-q 5,99 and -q6,00

Reply #3 – 2004-07-07 01:43:31

Actually lots of the -q6 files I've made with Megamix are smaller than my GT3b2 files at -q6.  Just something I've noticed.

-q 5,99 and -q6,00

Reply #4 – 2004-07-07 01:47:26

FWIW, I now have over 15GB of files encoded with Megamix. Average bitrate is exactly 192.