Hi everyone.
Mark posted my email to him on this list concerning the problem in the
subject, but now I'm on the list so I will be able to check out your
comments on this matter.
Go and download this WAV from
http://members.xoom.com/testwavs/test.zip - it is a short clip from
Metallica - The Small Hours. (about 700kb)
Now encode it with FhG mp3enc. At 192 and 256 kbps (with -qual 9) listen to
the left channel - the frequencies above 16kHz are echoed and swirled (I
don't know how to explain this, you will just have to listen). You should
use headphones because you will be able to hear it clearly. This
hi-frequency bug is not the decoder problem - I tried l3dec (v2.74) and
Winplay3 v1.4 (and winamp and sonique). Now with LAME you can hear the same
problem with 160kbps stereo (but in 160 j-stereo it's not there!), and at
192 and 256 it disappears (doesn't matter if it's j-stereo or stereo). On
other samples I tried you can hear the same bugs in 192 and 160 more or
less... so it's not a rule. At 256kbps these problems are completely gone.
But if you use VBR, in any mode (V 0-4), this problem always appears (in the
left channel)?? Maybe it is because when you use VBR, LAME cuts everything
above xy kHz but uses different bitrates
thus introducing these artifacts. As for CBR I don't know why they appear
(in the left channel) - maybe the bandwidth is too big?
And why it is only in the left channel? LAME handles this hi-frequency
problem better then FhG at every bitrate but the bug is still audible.
I also have one question (not related to the previous one): how come that
FhG MPEG-2 AAC (Liquid Audio) has such excellent pre-echo handling at low
bitrates like (128-160kbps)? Is this mainly because of the different format
(bitstream definition)?
---
Aleksandar
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MP3 ENCODER mailing list ( http://geek.rcc.se/mp3encoder/ )
