[LAU] Pro Audio? OT rant.

Fons Adriaensen fons at linuxaudio.org
Mon Dec 24 14:27:13 UTC 2012

On Mon, Dec 24, 2012 at 02:17:48AM -0500, Thomas Vecchione wrote:

> > So, consider a musician playing a Stradivarius violin. You'd want to be
> > able to reproduce all the tonal richness, and harmonics during the
> > recording phase. Some people say the ear can't hear above a certain
> > frequency anyway, so it doesn't matter whereas there are others who can
> > pick the difference between a Stradivarius violin and an "ordinary"
> > violin.
> The harmonics in question for a violin are all within the range of human
> hearing.  Harmonics occur at a regular mathematical interval above the
> fundamental frequency, and the fundamental frequency is generally very low
> in the range of our human hearing, for instance, since we are using a
> violin as an example, concert tuning a is only 440Hz, meaning your second
> harmonic occurs at 880, etc.  very low in the overall range of human
> hearing.
> The only exception to this I know of is when you have an interaction of two
> different frequencies that create a third 'phantom' frequency that can be
> lower than the fundamental of either of the other two (I know there is a
> better term for this, but the term I use to describe this in RF/wireless
> mics is harmonic intermodulation).

Violins (and many other instruments) can and do produce harmonics
above 20 kHz. As long as these are vibrations inside the instrument
they could even interact in non-linear ways and produce something that
is audible. Once they are 'in the air', they don't interact and you
can't hear them. 

The sound of a violin is determined by mainly two things (apart from
the skill of the player):

1. Body resonances. These depend on the construction and the
   materials used and can be very complex (complex as complicated).

2. The mechanical impedance at the bridge as seen by the strings.
   This is strongly related to (1) of course, depends on frequency
   and can be complex (complex as in maths). That means that the
   string will not have the same effective lenght at different
   frequencies, and harmonics need not be at exact integer
    multiples of the fundamental.

What sets a violins like a Stradivarius or a Guadagnini apart from
others is that they have the right combination of these properties,
one that is musically pleasing. What exactly those desirable traits
are in terms of (1) and (2) is still a matter of research. What is
certain is that you don't need any harmonics above 20 kHz in order
to hear the difference.

Last year I recorded six Guadagninis, the recording was explicitly
meant for research on their sound. The researcher wanted 48 kHz,
24 bit, a DPA omni mic and a strictly linear 'no tube nonsense'
preamp (I used an RME Micstasy). 



A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)

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