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Posted by Thomas
McGuire on November 14, 2001
Manufacturer: Terratec Product:
SoundSystem SiXPack 5.1+
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Hardware MP3 Decoding
Ironically one of the
neglected (well, unmentioned anyway) features of the SiXPack
5.1 is that of Hardware MP3 Decoding, which it offers via
the Microsoft DirectShow Interface. The SiXPack 5.1, along
with other CS4630 based Soundcards (SonicFury, Game Theater
XP, etc.) are the first consumer level Soundcards to offer
this. This offers reduced CPU usage during MP3 playback as
the Soundcard itself will be performing the decoding, rather
than the CPU.
Of course, much like
other “firsts”, how it works in reality is another
matter altogether. As mentioned in our Videologic SonicFury
& Game Theater XP review, the Hardware MP3 Decoding
feature only worked with Windows Media Player 6.4 & Voyetra
AudioStation 4.x. Unlike the Santa Cruz/SonicFury (But
like the Hercules Game Theater XP), TerraTec chose not to
offer either of these Media Players with SiXPack 5.1. This
shouldn’t be too much of an issue for most of you as
you’ll already have mplayer2.exe on your system,
which will provide one way to get Hardware MP3 Decoding.
Now that you can actually
take advantage of this feature you’ll find another
limitation. The Hardware MP3 Decoding can only be used for 1
song, which is ok if you intend to simply repeat 1 single
track with Windows Media Player 6.4, with AudioStation I
found that the decoding feature disabled itself after
the first track played.
Also, after several
minutes of playing an MP3 (Looped, or just a really long
one) the Audio quality would degrade with some audible
artefacts being introduced. The only way to remove these
would be to stop the track & restart it. Others have
experienced this with CS4630 Soundcards as well (As I have
with the SonicFury & Game Theater XP) so it would seem
to be a Hardware issue rather than a Driver one.
To see the beneficial
effect on CPU I tested the Hardware MP3 Decoding feature
both disabled & enabled in Windows Media
Player 6.4 (mplayer2.exe). Rather than re-run the tests
I’ve used my results based on tests with the Game Theater
XP. The MP3 used was 1.14 minutes long - 160 Kilobit,
16-Bit, 44.1KHz (Predator - The Chase – Alan Silvestri).
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Software
Decoded
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Hardware
Decoded
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Although the graphs above
do not indicate CPU % usage I can inform you that the peak
usage for the Software decoding was 12%, while the Hardware
decoded playback was only 4% at it’s highest. Based on
that you can clearly see that the Software (CPU) decoding of
the MP3 took on average 2 or 3 times greater CPU resources
than the Hardware decoding provided by the CS4630 DSP.
As
I already mentioned though, given the issues that exist with
the decoding feature TerraTec have perhaps chosen the right
path in ignoring to promote this feature. That said,
hopefully the next Cirrus Logic DSP will provide some manner
of improved MP3 Decoding capability, or at least provide one
compatible with a greater range of Applications, e.g.
Windows Media Player 7/8, Winamp & Real Player. This
also could be of greater benefit given a lot of Games now
use MP3 Soundtracks, e.g. Tribes 2, Sacrifice & Rally
Championship Xtreme (This Game as it happens uses the
highest quality MP3s in any Game I own thus far – 320
Kilobit, 16-Bit, 44.1KHz).
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