Re: [linux-audio-dev] AC3 encoder for Linux? AAC vs MP3 vs MP2 quality :-)

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Subject: Re: [linux-audio-dev] AC3 encoder for Linux? AAC vs MP3 vs MP2 quality :-)
From: Benno Senoner (sbenno_AT_gardena.net)
Date: su tammi  09 2000 - 19:26:54 EST


On Sun, 09 Jan 2000, Erik de Castro Lopo wrote:
> Adam Williams wrote:
> >
> > Anyone know of an AC3 encoder for Linux? I'm well aware of the AC3
> > decoder, but a decoder isn't much use without an encoder.
>
> Is AC3 the same as AAC? If it is, have a look at:
>
> http://www.slimline.net/aac/
>
> for an encoder and decoder which will compile under Linux.
>
> Erik

No,
 AAC is not AC3 !

AAC is a descendent of AC3 but takes ideas from MPEG audio too

AAC is not backwards compatible with MP2/MP3 nor AC3.

Independent tests showed that the Fraunhofer AAC encoder ( AAC main
developed by a joint venture of Fhg, Sony, Philips etc ..) ,
with a bitrate of 128Kbit gives statistically indistinguishable results from
CD audio.
(there are some differences but these are not perceived as "annoying").

For comparison MP3 needs at least 192-256kbit in order to give the same
audio quality.

The ISO reference encoder doesn't sound very good, I don't know the code
mentioned at the link.
I think Fraunhofer & friends will not give us a free high-quality AAC encoder,
therefore it's very likely that if you want to get this "indistingushable from
CD" quality the only way is to buy a commercial encoder (not available yet I
think).

IMHO with all these patent issues and HUGE encoding time, AAC is actually
not worth a 30% data reduction ( AAC at 128kbit should sound as good as
MP3 at 192kbit).

But if you ask me, for professional broadcasting ( DMX satellite radio , etc)
MPEG Layer II ( MP2) will still rule for a long time even if the compression
rate is only 1:4 - 1:6.

In a few special cases you can cheat the mp3 encoders (square waves
for example), producing very bad S/N ratio.
MP2 is much more stable in these cases.

I remember some time ago I had a discussion with one of the RME-audio people
about MP3 @ 128kbit = TRUE CD QUALITY (he tried to convince me that
he was right),
but when I showed him some cases ( 50Hz square wave for example),
then he capitulated.
:-)

A friend of mine owns a disco pub and uses a PC to play the music,
the uses MP2 @ 384kbit , I compared the same tunes with MP3 @ 128kbit and
there is really a noticeable difference when listening at VERY loud volumes.
The song in MP2 feels stronger and with more dynamics,
and I think people get less headaches when listening to MP2 for 1-2 hours
(at these loud volumes) instead of listening at MP3.

Sorry for going a bit off-topic, but people doesn't tell you always the whole
truth about compression.

anyone who agrees on my points ?

Benno.


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