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  • Questions Re: Air Absorption Filter


    I understand that this feature reduces the high frequencies of an instrument the further the instrument gets from the main mic aray in order to simulate air absorption. What EQ curve is used here? Because it is extremely subtle. And if I wanted to exaggerate this effect, I would like to use the setting that VSL landed on but more exaggerated.


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    Back in the days, we deliberately opted for an implementation that was both useful and simple to use as well as economical (in terms of CPU cycles). We came up with a smooth and efficient filter that enhances the sense of distance while keeping the actual sound of the source signal intact. However, there aspects such as temperature and humidity that are considered to be influencing factors from a scientific point of view, which we have simply ignored. 😊

    For a more detailed parameterization and a more pronounced effect, I recommend the use of specialized plug-ins such as Sound Particles' "Air", therefore. It's easy to estimate the distance between a MIR Icon and the Main Microphone by means of the 1x1 meters grid overlay in MIR's Venue Maps.


    /Dietz - Vienna Symphonic Library

  • /Dietz - Vienna Symphonic Library
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    JBuck, I've usually made do with a 6dB/octave high cut filter and simply dialed it in (i.e. adjusted the frequency roll-off point) until the HF attenuation sounds plausible - or like what I want - for the distance I'm setting up. In my book, 6dB/octave is a practical and reasonable approximation of the scientific data for frequencies above 1 kHz.

    Distance without taking into account air absorption, on the other hand, is usually reckoned as 6dB reduction for every doubling of distance - assuming spherical spreading from the sound source.

    Yes air absorption of audible sound is subtle within the distances most of us here are working with. For example, at 0% Relative Humidity and 20ΒΊC, air absorption is only about 5 dB/kilometre at 2Khz, and 30 dB/kilometre at 10kHz. (Unfortunately, hardcore scientific data sets on air absorption are locked behind paywalls and subject to strict copyright, so I'll desist from quoting any more data here.)

    I see above that the "Air" plugin from Sound Particles has been mentioned (the "Air - Music Edition" version is free and good enough for our purposes). I have it and it's a potentially very useful plugin because you can use it either for air absorption only, or else combine air absorption-attenuation with normal distance-attenuation also. That said, I still use the simple old-fashioned single-pole high-cut filter solution, because like you, I sometimes want to play around with the HF roll off; but maybe for some purposes I'll switch over to using the Air plugin later on.

    "The US 1st Amendment does NOT allow you to yell "FIRE!" falsely in a packed cinema, nor in an online forum." ~ Dobi (60kg Cane da pastore Maremmano-Abruzzese)
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    Thanks @Dietz and @Helmholtz

    I'll be sure to check out everything you have mentioned above. And I'm looking forward to some experimentation.