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Topic: Lowpass Bug? (Read 2975 times) previous topic - next topic
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Lowpass Bug?

If I use --lowpass 20 or --lowpass 20,5 Lame reports the same transition band..

--lowpass 20000
Code: [Select]
C:\audiograbber\Test>LAME Fighter.wav --lowpass 20000
LAME version 3.90.3 MMX  (http://www.mp3dev.org/)
CPU features: i387, MMX (ASM used), SIMD
Using polyphase lowpass  filter, transition band: 20094 Hz - 20627 Hz
Encoding Fighter.wav to Fighter.wav.mp3
Encoding as 44.1 kHz 128 kbps j-stereo MPEG-1 Layer III (11x) qval=5
    Frame          |  CPU time/estim | REAL time/estim | play/CPU |    ETA
   150/9532   ( 2%)|    0:01/    1:30|    0:01/    1:30|   2.7401x|    1:29


--lowpass 20500
Code: [Select]
C:\audiograbber\Test>LAME Fighter.wav --lowpass 20500
LAME version 3.90.3 MMX  (http://www.mp3dev.org/)
CPU features: i387, MMX (ASM used), SIMD
Using polyphase lowpass  filter, transition band: 20094 Hz - 20627 Hz
Encoding Fighter.wav to Fighter.wav.mp3
Encoding as 44.1 kHz 128 kbps j-stereo MPEG-1 Layer III (11x) qval=5
    Frame          |  CPU time/estim | REAL time/estim | play/CPU |    ETA
   150/9532   ( 2%)|    0:01/    1:37|    0:01/    1:37|   2.5444x|    1:36


Same problem with 3.92, both CBR and VBR..
Is it a bug?
[ Commodore 64 Forever...! ]

Lowpass Bug?

Reply #1 –
Quote
20094 Hz - 20627 Hz

Yep, I can believe that.


Ssshhhhh!  Keep it quiet until someone claims that a lowpass of 20khz is not enough, that they cant hear the top end, and yet, with 20.5khz, that issue is gone  :-D

Lowpass Bug?

Reply #2 –
Quote
Same problem with 3.92, both CBR and VBR..
Is it a bug?

No, this is normal. LAME has some lowpass thresholds, anything above or below that will be rounded up or down. It's not as flexible as the --lowpass switch suggests.

Lowpass Bug?

Reply #3 –
The output should be different isn't it?
[ Commodore 64 Forever...! ]

Lowpass Bug?

Reply #4 –
Quote
The output should be different isn't it?

As far as I have understood it should be completely the same. Why don't you just do a file compare?
They should be identical.

Lowpass Bug?

Reply #5 –
I've compared the files, they are identical..

When (for example) lowpass 19 and 19,5 produce different output..
[ Commodore 64 Forever...! ]
 

Lowpass Bug?

Reply #6 –
Quote
Quote
Same problem with 3.92, both CBR and VBR..
Is it a bug?

No, this is normal. LAME has some lowpass thresholds, anything above or below that will be rounded up or down. It's not as flexible as the --lowpass switch suggests.

And the steps/values you can use with the lowpass option are:

21.8
21.1
20.4
19.6
18.9
18.2
17.5
16.8
16.1
15.4
14.7
14.0
13.2
12.5
11.8
11.1
10.4
9.7
9.0
8.3
7.6
6.8
6.1
5.4
4.7
4.0
3.3
2.6
1.9
1.2
0.4