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strange results using low-pass filter ( lame 3.98/3.99.5 )
paracent
post Aug 14 2013, 20:42
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Hello,

For encoder(s) testing purpose I created a 19.3kHz >>tone<< , 48kHz, 10 sec sample wav file., using 'sox'.
After a number of different tests for quality/sound reproduction ( doing on aac he/h2 & ogg ) I decided to test it on mp3 using lame 3.98 & 3.99.5
All samples were imported into 'baudline' to build a spectrogram. ( total about 50 )
when I got to lame, I set the low-pass filter to 19.5, 20, 21, and 22kHz, after importing the 20 and lower low-pass samples into baudline, my first words were: WTF?

here is the original WAV: ( all just 19.3khz tone )


this is a 48kHz / 21kHz low-pass MP3: ( lame )


this is the, same sample, but 19.5kHz low-pass ( lame ) ( this is when I asked WTF? )



in all test cases for OGG / AAC / MP3 I encoded to the specific format, and back to WAV - to make sure the results are constant, using ffmpeg to reencode )
even if I do not re-encode back to wav, the results are the same on LAME for low-pass lower, or equal to 20kHz.

now, this is just one tone 19.3kHz... Imagine, all the music collections converted to MP3... using lo-pass 20kHz or lower.

The tests I am doing are about the encoder accuracy, and of course, if the accuracy is higher, quality of the encoded file will be also better.
So far, the results I got, put WAV, FLAC and OGG as the most accurate, closest to the original sample formats. ( various samples, including single, high freq. tone(s) )

None of other formats I have been working on shows such "strange" behavior...

If anybody has an explanation, to my "WTF" question, I would really appreciate....

Mike

edit:
used the following LAME opts:

lame -V0 --lowpass 19.5 output.wav output_v0_lp19.5_99lame.mp3
and
lame -V0 --lowpass 21 output.wav output_v0_lp21_99lame.mp3


This post has been edited by paracent: Aug 14 2013, 20:48
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Posts in this topic
- paracent   strange results using low-pass filter ( lame 3.98/3.99.5 )   Aug 14 2013, 20:42
- - saratoga   Clipping? If you use a tone at -6dB does it work ...   Aug 14 2013, 21:26
|- - paracent   well, this is not about clipping... look at the l...   Aug 14 2013, 21:35
||- - saratoga   QUOTE (paracent @ Aug 14 2013, 16:35) loo...   Aug 14 2013, 21:41
||- - paracent   no, there is no clipping, and even assumption is n...   Aug 14 2013, 21:52
||- - db1989   QUOTE (paracent @ Aug 14 2013, 21:52) no,...   Aug 14 2013, 22:49
|- - DonP   QUOTE (saratoga @ Aug 14 2013, 16:26) Cli...   Aug 14 2013, 21:53
- - mixminus1   QUOTE Imagine, all the music collections converted...   Aug 14 2013, 21:50
|- - saratoga   QUOTE (paracent @ Aug 14 2013, 16:52) no,...   Aug 14 2013, 23:06
|- - paracent   Did more tests.. Well, without lowering by -3dB, ...   Aug 15 2013, 00:05
|- - greynol   QUOTE (paracent @ Aug 14 2013, 16:05) loo...   Aug 15 2013, 00:11
|- - paracent   I guess a better place to ask this question would ...   Aug 15 2013, 00:30
||- - greynol   QUOTE (paracent @ Aug 14 2013, 16:30) TOS...   Aug 15 2013, 00:33
||- - db1989   QUOTE (paracent @ Aug 15 2013, 00:30) on ...   Aug 15 2013, 00:36
||- - greynol   QUOTE (db1989 @ Aug 14 2013, 16:36) imply...   Aug 15 2013, 00:40
|- - 2Bdecided   QUOTE (greynol @ Aug 15 2013, 00:11) QUOT...   Aug 15 2013, 13:43
|- - Rescator   QUOTE (2Bdecided @ Aug 15 2013, 14:43) th...   Aug 15 2013, 16:52
- - greynol   Yet another example of someone not understanding l...   Aug 14 2013, 23:49
- - Propheticus   If you actually read tos 8 you'd see it's ...   Aug 15 2013, 00:42
- - greynol   FWIW, I don't think this is resulting from cli...   Aug 15 2013, 00:47
|- - greynol   QUOTE (greynol @ Aug 14 2013, 16:47) FWIW...   Aug 15 2013, 16:52
|- - Rescator   QUOTE (greynol @ Aug 15 2013, 17:52) Rega...   Aug 15 2013, 17:45
|- - db1989   Clipping in the mastering stage, which necessarily...   Aug 15 2013, 17:50
|- - Rescator   QUOTE (db1989 @ Aug 15 2013, 18:50) Clipp...   Aug 15 2013, 18:43
- - Makaki   This discussion would be a lot more useful if some...   Aug 15 2013, 00:57
- - greynol   If it hurts when you "lame.exe --useless --ad...   Aug 15 2013, 01:14
- - paracent   QUOTE (greynol @ Aug 14 2013, 19:40) QUOT...   Aug 15 2013, 05:39
|- - saratoga   QUOTE (paracent @ Aug 15 2013, 00:39) QUO...   Aug 15 2013, 07:32
|- - greynol   QUOTE (paracent @ Aug 14 2013, 21:39) are...   Aug 15 2013, 14:41
- - [JAZ]   QUOTE (paracent @ Aug 15 2013, 01:05) - w...   Aug 15 2013, 12:00
|- - db1989   QUOTE ([JAZ] @ Aug 15 2013, 12:00...   Aug 15 2013, 12:55
- - paracent   perfect, "start getting somewhere" sound...   Aug 15 2013, 13:17
|- - db1989   I agree with everything David said. And yes, parac...   Aug 15 2013, 14:02
- - paracent   "Generally, especially when you don't kno...   Aug 15 2013, 14:45
- - paracent   "How I encode my music is determined through ...   Aug 15 2013, 14:51
|- - greynol   QUOTE (paracent @ Aug 15 2013, 06:51) Whe...   Aug 15 2013, 15:04
||- - paracent   QUOTE (greynol @ Aug 15 2013, 10:04) QUOT...   Aug 15 2013, 15:15
|- - 2Bdecided   QUOTE (paracent @ Aug 15 2013, 14:51) bes...   Aug 15 2013, 16:17
- - greynol   You didn't answer either of my questions. Do ...   Aug 15 2013, 15:26
- - [JAZ]   On the technical side of the problem: I believe t...   Aug 15 2013, 15:41
|- - paracent   QUOTE ([JAZ] @ Aug 15 2013, 10:41...   Aug 15 2013, 15:50
- - paracent   Gargamel: "Humor me" - This would be off...   Aug 15 2013, 15:42
|- - db1989   QUOTE (paracent @ Aug 15 2013, 15:42) ...   Aug 15 2013, 15:44
- - paracent   db1989 - I am no here to find amusement, an not he...   Aug 15 2013, 15:53
|- - dhromed   Unless I'm way off base, the pictures look lik...   Aug 15 2013, 16:08
- - db1989   What was wrong with the request to confirm that th...   Aug 15 2013, 15:58
- - [JAZ]   It is a property of the implementation that is use...   Aug 15 2013, 16:01
- - db1989   Nope, according to the OP, it was a sustained tone...   Aug 15 2013, 18:48
- - greynol   It's a full-scale sinusoid, not an impulse, bu...   Aug 15 2013, 18:52
- - BFG   How's it sound in lame 3.100a2? (I'd also...   Aug 16 2013, 04:43
|- - greynol   QUOTE (BFG @ Aug 15 2013, 20:43) How...   Aug 16 2013, 14:47
|- - BFG   QUOTE (greynol @ Aug 16 2013, 08:47) QUOT...   Aug 17 2013, 01:04
- - Gecko   Using the foobar ABX component, the provided mp3 f...   Aug 16 2013, 11:58


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