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LAME, CBR, VBR,.... I'm confused!
Immo
post Mar 26 2003, 19:51
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Hi!

This is my first post on this board, and the reason why I'm posting is to find an explanation for one particular, interesting issue of LAME MP3 compression...

I took a sample from a live instrumental concert with clear high-frequency sounds. I compressed it with two different settings, using LAME 3.91.

-b 192 -m j -h -q 0 (= 192kbps constant, joint stereo, quality-optimised, max. quality) and
--alt-preset standard, which produced a slightly larger file, the bitrate averaging at 200kbps.

The results were both quite good and I couldn't tell the difference in sound - maybe I lack the equipment.

I performed a spectral frequency analysis on each of the results.

Here's what it looked like:


Let's look at the left image: the frequency meter suggests thet there's a sharp cut at 16kHz. Nevertheless, some sounds are given higher frequencies, but then there is another sharp cut just under 19kHz, above which nothing can be seen.

Now the right image: up to about 16kHz the frequencies are generally preserved. Then they gradually become thinner in a varying manner, depending, i suppose, on their importance. There is no sharp cut below ~19.8kHz.

I do not know much abot audio compression - maybe I'm misunderstanding the whole thing - so I'd like you to ask you first: which picture do you think corresponds to which compression method?

Immo
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Pio2001
post Mar 26 2003, 21:12
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The left picture must be alt preset standard, because the lowpass is lower (18671 to 19205 Hz, vs 19383 to 19916 Hz for the other command line).

Nothing can be said about quality or audible difference looking at the pictures, because an MP3 encoder is targeted at removing as much inaudible sounds as possible. Therefore a lack of frequencies can as well mean that some audible parts are missing (bad work, or too low setting), than that the encoder managed a very good compression, removing a lot of unuseful things.

BTW, there are also alt presets for CBR, that provide better quality than your command line. the syntax is --alt-preset CBR 192, and, according to http://www.hydrogenaudio.org/forums/index....=ST&f=15&t=3076 , and to the verbose switch, it means

-h -b 192 --nspsytune -m j --lowpass 19500 --athtype 2 --ns-bass -6 --scale 0.97

There must be a slight difference in one of the settings, since I get is different files with the preset and the command line (JohnV ? Dibrom ?)

And before you ask, there is no equivalent command line to the VBR alt presets (FAQ)
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Posts in this topic
- Immo   LAME, CBR, VBR,.... I'm confused!   Mar 26 2003, 19:51
- - /\/ephaestous   YOU CANT' SAY SOMETHING SOUNDS BETTER BASED ON...   Mar 26 2003, 19:59
- - ff123   I'd say that --alt-preset standard is the pict...   Mar 26 2003, 20:46
- - evereux   QUOTE (/\/ephaestous @ Mar 26 2003 - 06:...   Mar 26 2003, 21:08
- - Pio2001   The left picture must be alt preset standard, beca...   Mar 26 2003, 21:12
- - outscape   i have to agree with /\/ephaestous on this.. ...   Mar 26 2003, 21:18
- - /\/ephaestous   QUOTE (evereux @ Mar 26 2003 - 03:08 PM)QUOTE...   Mar 26 2003, 21:21
- - Immo   Thanks for the replies, folks. All who guessed, g...   Mar 26 2003, 22:11
- - Andavari   QUOTE (Immo @ Mar 26 2003 - 03:11 PM)The poin...   Mar 26 2003, 22:38
- - [proxima]   QUOTE (Pio2001 @ Mar 26 2003 - 09:12 PM)-h -b...   Mar 26 2003, 23:11
- - LordSyl   Please, don't confuse newbies with those stupi...   Mar 26 2003, 23:54
- - Pio2001   Right, right, It started when I was about to write...   Mar 27 2003, 00:30
- - mithrandir   QUOTE (Immo @ Mar 26 2003 - 04:11 PM)A questi...   Mar 27 2003, 01:43
- - NeoRenegade   I just wanted to point out, Immo, that your comman...   Mar 27 2003, 06:46
- - Immo   Good afternoon, thanks for the tip, NeoRenegade, ...   Mar 27 2003, 13:08
- - Pio2001   QUOTE (Immo @ Mar 27 2003 - 03:08 PM)I suppos...   Mar 27 2003, 14:28
- - Immo   Sorry, you're right! What I meant was th...   Mar 27 2003, 15:12
- - Lev   /\/ephaestous: QUOTE YOU CANT' SAY SOMET...   Mar 27 2003, 17:36
- - Gecko   Immo: VBR isn't about preserving HF content. I...   Mar 27 2003, 17:58
- - Immo   Lev: it gets even more ironic when the author make...   Mar 27 2003, 18:39
- - deej_1977   QUOTE (Pio2001 @ Mar 27 2003 - 03:28 PM)Addin...   Mar 27 2003, 18:47
- - LordSyl   CBR is shit...always. The entire fact of giving th...   Mar 27 2003, 19:30
- - sony666   CBR is not "always shit", plz stay serio...   Mar 28 2003, 01:58
- - NeoRenegade   The lame development team works on the encoder and...   Mar 28 2003, 03:29
- - roman   To Immo About your 1st pictures... Can you think a...   Mar 28 2003, 08:38
- - Oge_user   QUOTE (Immo @ Mar 27 2003 - 12:08 PM)I tried ...   Mar 28 2003, 10:52
- - DigitalDictator   sony666 QUOTE If you plan to use your encodes for...   Mar 28 2003, 11:57
- - Immo   Roman: I guess ti prav explaining how VBR acts ...   Mar 28 2003, 19:12
- - Immo   Oge_user:I just tried it, the results weren't ...   Mar 28 2003, 19:25
- - sony666   QUOTE (DigitalDictator @ Mar 28 2003 - 11:57 ...   Mar 28 2003, 23:48


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