[vorbis] Difficult sample for vorbis w/ audible artifacts

[Wilson]

I grabbed the WAV, and encoded it with the latest Oggdrop at 350kbps. I
dragged 5 instances of the WAV file, and 5 instances of the Ogg file into a
Winamp playlist, and randomized it. I don't hear any artifacts in the Ogg
file..
Next, I encoded the WAV file to a 128kbit VBR MP3 with RazorLame, and into a
128kbit Ogg file with Oggdrop 1.0b4. I put three instances of each into a
Winamp playlist, and 3 instances of the WAV file. Hit randomize, turned up
the volume, closed my eyes, hit play. I really don't hear any artifacts.
Admittedly, I'm using Klipsch Promedia 4.1s.. Not reference quality stuff. I
left my Sennheisers at work today.. I get the impression from your message
that it's not supposed to be that subtle.
If it would help, I could make my mp3 and ogg test tracks available to you..

----- Original Message -----
From: "Darin Morrison" <dibrom at moscow.com>
To: <vorbis at xiph.org>
Sent: Friday, June 15, 2001 2:17 PM
Subject: [vorbis] Difficult sample for vorbis w/ audible artifacts

> I came across an interesting test sample the other day while trying to
> compress some of my music and trying out different encoders.  You can grab
> the sample in question from here:
>
> http://www.animus-facticius.org
>
> drone_clip.zip is a 9 second clip of the track where the artifact is most
> apparent, drone_short.pac is a 1 minute clip of track.  The sample is from
> the song "Drone" from "Autechre - Peel Session". The longer clip is
> compressed with LPAC which can be found here:
>
> http://www-ft.ee.tu-berlin.de/~liebchen/lpac.html
>
> Basically, what happens is when encoding this file at lower bitrates with
> vorbis beta 4 there is some very bad pre-echo on the sharp attacks.  I
have
> been told that pre-echo handling is still being worked on though so maybe
> there is not much that can be done yet.  I was told something about
wavelets
> being implemented in the future, possibly after 1.0, and that this might
> make a difference?  The majority of the pre-echo does go away as the
bitrate
> increases but its still not perfect.  The other artifact doesn't go away
no
> matter what the bitrate is (I tried -b 350).  It sounds like low frequency
> noise or vibration, or maybe some sort of "squeak" on the bass pulses.
>
> I have also tested this sample with both mp3 and AAC and they both did
quite
> poorly, the only codec that seems to be able to handle this perfectly is
> mp+/mpc.  Vorbis is in my opinion the second best though on this sample
> though, by quite a bit.  I was quite surprised to see how well it actually
> did after most others failed.  Anyway, maybe one of the developers can
take
> a look at this sample and see if there is anyway to improve vorbis to
handle
> this better or something like that.  I have heard of some other low
> frequency artifacts on heavy bass notes with vorbis in the past but I'm
not
> sure if they were supposed to have been addressed yet or not, and I'm not
> positive this case is caused by the same thing either.
>
> There has already been some discussion about this clip on the r3mix.net
> forum for those interested, though it has mainly been centered around mp3.
> There is some mention of testing it with vorbis in there however:
>
> http://66.96.216.160/cgi-bin/YaBB.pl?board=c&action=display&num=992254752
>
> Dibrom
>
>
>
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