On 2015-04-23, Stefan Schreiber wrote:
How can this be if there are no fundamentals in this range? (See my list of piano keys/frequencies. Some instruments go down to about 30Hz. Organs can go even lower, but this is already one of the non-typical cases....)
That stuff is indeed there and mostly comes from percussion. The reason is that transients, being limited in time, don't break down into a discrete spectrum of harmonics, but into a continuous one which spreads out in inverse proportion to their temporal extent. (That's the uncertainty principle at work; it in fact has nothing to do with physics per se, but the properties of the Fourier transform and its time-frequency duality.)
One way to see how that happens in practice is when you consider how a kick drum operates. When the mallet hits the membrane, it tries very hard to produce a step amplitude waveform, which of course has a spectrum reaching right downto DC. That then gets filtered by the broad modal structure of the drum itself, so that you get a broad band of energy mostly centered around the first mode of the instrument, plus some modulation of the parameters because the mallet pressing on the membrane initially tensions it more and heightens resonance structure in frequency. The result then couples in a frequency dependent manner to air, leading to extra low end rolloff because of the finite size of the instrument. To a first approximation you get something like a rapid downward chirp with a broad formant around the first mode, and energy arbitrarily low below that arbeit at progressively lower levels.
On the Fourier side of things, sharply cutting off the LF content leads to low frequency ringing just as cutting HF content does on the other end. Because of the longer wavelength, though, in the time domain such manipulation reaches much farther away. So, paradoxically, a setup which (phase linearly/coherently) reproduces very low bass doesn't so much sound bassier, but causes LF transients to be better localised in time. That is, snappier and more kick than boom like. That's then why techno fiends like me favor setups without separate subs, closed designs instead of reflex ones, high damping and so on: the lower you can go and with the more gentle rolloff (which in a minimum phase system automatically leads to less phase dispersion), the better defined and the more energetic the beat.
-- Sampo Syreeni, aka decoy - de...@iki.fi, http://decoy.iki.fi/front +358-40-3255353, 025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2 _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe here, edit account or options, view archives and so on.
