[vorbis] Spectrum duplication (2)

Sune Foldager cryo at diku.dk
Tue Jun 17 05:13:21 PDT 2003

Headless wrote:

>> The backward compatibility stuff, no. But a technique that can maybe
>> improve percieved quality? Would make sense to consider it at least.
>> IMHO.
> For me Ogg V1 equaled the performance of MP3Pro at low bitrates when I
> compared some 70 sound samples. So imo there's nothing to fix.

I wasn't talking about fixing, but about improving. It must always be a 
goal to improve the perceived quality per bit, as I see it :-).

>> Right.. but none the less, they made AACpro or whatever it's called,
>> which apparently employes the same "technology", viz. the spectrum
>> duplication stuff, to improve on AAC's quality in low bitrates.
> AAC suffers for the same problem that MP3 suffers from, it's an old
> format that isn't efficient enough by modern standards. Thus it
> performed badly when compared to modern encoders, hence it needed a
> similar sort of "fix" for it to remain competitive.

I was under the impression that AAC was one of the "second generation" 
codecs. It's certainly much newer than mp3, and to the untrained 
listener such as myself, it sounds exactly similar to mp3 at say around 
64kbit/sec, but much better than mp3 at the same bitrate. Apparently 
they still applied the spectrum duplication/replication whatever to it. 
I am sure that _I_ can't tell the difference between AAC at 64kbit, and 
AACplus (as I think they called it) at the same bitrate, but I don't 


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