[LAU] Rolling off high frequencies when mastering?

[Niels Mayer]

Monty Montgomery <xiphmont at gmail.com>:

> Energy is preserved, even at the exact nyquist frequency, however

modulating the input signal against the sampling clock results in the

signal being partly shifted to DC.  The signal energy is there... it

appears somewhere else.


I bet a scientist could come up with a wacky experiment to disprove your
assertion that nyquist is the only thing that mattered.

For example, assuming one had a way of "playing back" in real-time, echoes
of what a bat would hear as it flew around a room of known geometry....
Consider an experiment:

Record/playback one using the "pure nyquist" hypothesis, and therefore
containing only "energy" or real-plane information.

Record/playback another assuming "nyquist++" -- nyquist theory augmented by
hypothesis that both real and imaginary plane information can be perceived
by mammals with advanced hearing capabilities (dogs, bats, humans,
dolphins).

Do the bats virtually "fly into walls" when presented with "pure nyquist"
virtual audio world?
Or do they navigate correctly when presented with sampled/reconstructed
representations that had concern over both real and imaginary plane info?
(aka phase matters, esp at high frequencies, and therefore you need much
higher sampling rates).

Note that the experimental subject, being a bat, is  probably unbiased to
the argument at hand. Further, no double-blinding is needed because, again,
they're bats :-).

This is utter hogwash.  All the signal energy and resolution is

preserved to exactly the limits of the sampling rate at all lower

frequencies, even if your 'biggest dots' aren't landing at 0dB or

wherever.  True of audio signals, true of  images, true of video.  The

same discrete sampling lessons apply to all three equally.


Prove it! I don't need another paper telling me about nyquist or how
compression works. Until you have a proper model of human perception, this
kind of cocky blinded-pseudo-rationalism, or repeating the same old tired
truisms -- is just a waste of everybody's time. Nyquist is at best a
sophomoric model of the *human* perception of sound, the biological
perception, of the "energies" you're talking about. It's like Marie Curie
saying "well it only fogs the film"... yeah, and in biological organisms it
causes cancer -- because it's not just the energy, it's also the frequency
(and in this argument, phase).

Furthermore, your perspective totally ignores the fractal nature of reality
-- of nature. And of sound.
Fractal image compression is resolution independent and works precisely
because it better models real-plane and intra-dimensional aspects of reality
that you've decided to rationalize away. You claim this is true for images
and video too: How does it work in fractal compression? (
http://en.wikipedia.org/wiki/Fractal_compression ).

And when you think about it fractals, and not "masking" is the correct way
to compress sound, as it's most likely directly involved in our ability to
perceive sound: Ultimately, the brain isn't masking anything, it's taking
each instrument heard and "triggering" the fractal-equation that would
generate it's sound. So if we perceive sound as a bunch of activated fractal
recognizers -- the fractal that generates the "bass" sound... the fractal
that generates the "drum" --- our brain reconstructs the missing pieces no
matter what. Just like a broken hologram can still reconstruct the original
image.

See also Michael Barnsley's "Fractals Everywhere" (it's on my nightstand
now, alongside David Wright's "Mathematics and Music"). Or one of the most
mind-blowing papers ever:
http://www.ams.org/notices/201001/rtx100100010p.pdf
"The Life and Survival of Mathematical Ideas" Michael F. Barnsley. (and also
in the same issue http://www.ams.org/notices/201001/rtx100100030p.pdf )

Niels
http://nielsmayer.com
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