[vorbis-dev] Spectral band replication

[Philip Cowles]

This idea worries me.  Its the harmonics that defines all sound.  Pure sine waves
are very rare.  Take two instruments, say, a flute and a bongo.  They might play
the same fundamental note but how do we tell them apart?  It's all in the
harmonics. The flute does things in a (roughly) linear air column modified by the
flute's structure and by its stops, the bongo tends to worship Bessel, but with
some dissent, again due to interactions with it's structure and non-linear air.

A more subtle example might be the difference between a Stradivari and a Guarneri
violin. These guys didn't just chuck harmonics in using a simple algorithm but
the buffs can tell the difference.

Then, there is the fundamental razor -- good ol' Nyquist.  If you sample at a
certain rate, anything you bung in afterwards is just noise.  You invented it
chum.  But -- do we want spurious musical inventions?  Is this the point of OGG?

Gustav The Lemming

"Stefan T. Böttner" wrote:

> Hello!
> I have the following idea about this "spectral band replication":
>
> Harmonic frequencies are integer multiples of the fundamental frequency. That
> means if you take all frequencies in a particular block (say up to 11 KHz for
> a medium bitrate encoding), double them and add them to the original at a
> lower volume, then this results in frequencies up to 22 KHz.
>
> I suppose that taking anything else but harmonics will rather end up in more
> noise. And don't know if that's it what mp3pro does, because I didn't find
> any details, and they probably won't give them out.
>
> I already tried this with music that I downsampled to 11 KHz, i.e.
> frequencies up to 5.5 KHz, and it did sound much better when adding the
> harmonics x2, x3, x4 or even more.
>
> Stefan T. Boettner
>
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