30 Jan
2009
30 Jan
'09
4:14 p.m.
hi everybody!
does anyone know a way to compute filters that simulate air dissipation
for a given temperature and humidity?
so far, all i've found is an online calculator at
http://www.sengpielaudio.com/calculator-air.htm, but the javascript in
there is not exactly fit for citation :)
plus i know there is a standard (ISO 9613-1:1993) that deals with sound
attenuation, but i don't have access to a standards library and don't
feel like buying it...
a rough calculation at 18°C and 85% relative humidity (using sengpiel's
tool) yields:
f[Hz] dp[dBSPL/m]
----------------------
20 0
40 0
80 0
160 0
320 0.001
640 0.003
1280 0.006
2560 0.011
5120 0.032
10240 0.112
20480 0.404
which indicates that for my usecase (close-miked sounds that need to be
placed at distances between 10 and 45 m), the air-damping non-linearity
is really important.
question is: how do i design a filter to simulate this? would make a
cool ladspa tool eventually...
pointers to related papers or maybe even filters are most welcome.
best,
jörn
30 Jan
30 Jan
4:44 p.m.
you can try using a bank of equaliser filters in parallel? The
Regalia and Mitra design ("Tunable Digital Frequency Response Equalization
Filters", IEEE Trans. on Ac., Sp. and Sig Proc., 35 (1), 1987) works
quite well.
Victor
----- Original Message -----
From: "Jörn Nettingsmeier" <nettings(a)folkwang-hochschule.de>
To: "The Linux Audio Developers' Mailing List"
<linux-audio-dev(a)lists.linuxaudio.org>
Sent: Friday, January 30, 2009 8:15 PM
Subject: [LAD] sound dissipation in air - formulas and filters?
hi everybody!
does anyone know a way to compute filters that simulate air dissipation
for a given temperature and humidity?
so far, all i've found is an online calculator at
http://www.sengpielaudio.com/calculator-air.htm, but the javascript in
there is not exactly fit for citation :)
plus i know there is a standard (ISO 9613-1:1993) that deals with sound
attenuation, but i don't have access to a standards library and don't
feel like buying it...
a rough calculation at 18°C and 85% relative humidity (using sengpiel's
tool) yields:
f[Hz] dp[dBSPL/m]
----------------------
20 0
40 0
80 0
160 0
320 0.001
640 0.003
1280 0.006
2560 0.011
5120 0.032
10240 0.112
20480 0.404
which indicates that for my usecase (close-miked sounds that need to be
placed at distances between 10 and 45 m), the air-damping non-linearity
is really important.
question is: how do i design a filter to simulate this? would make a
cool ladspa tool eventually...
pointers to related papers or maybe even filters are most welcome.
best,
jörn
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Linux-audio-dev mailing list
Linux-audio-dev(a)lists.linuxaudio.org
http://lists.linuxaudio.org/mailman/listinfo/linux-audio-dev
5:08 p.m.
On Fri, Jan 30, 2009 at 09:15:10PM +0100, Jörn Nettingsmeier wrote:
so far, all i've found is an online calculator at
http://www.sengpielaudio.com/calculator-air.htm, but the javascript in
there is not exactly fit for citation :)
plus i know there is a standard (ISO 9613-1:1993) that deals with sound
attenuation, but i don't have access to a standards library and don't
feel like buying it...
a rough calculation at 18°C and 85% relative humidity (using sengpiel's
tool) yields:
f[Hz] dp[dBSPL/m]
----------------------
20 0
40 0
80 0
160 0
320 0.001
640 0.003
1280 0.006
2560 0.011
5120 0.032
10240 0.112
20480 0.404
which indicates that for my usecase (close-miked sounds that need to be
placed at distances between 10 and 45 m), the air-damping non-linearity
is really important.
Put the lines (the nunbers) above in a separate
text file, and plot with gnuplot using a log x
scale, e.g. to see the effect at 20 meters:
plot 'thefile' u 1:($2)*20 w l 3
This will show you that a simple 2nd order
lowpass will do the job - it's not a perfect
match but good enough. It's not critical at
all - for small distances you can even use
a standard shelf or parametric.
Ciao,
--
FA
Laboratorio di Acustica ed Elettroacustica
Parma, Italia
O tu, che porte, correndo si ?
E guerra e morte !
31 Jan
31 Jan
8:14 a.m.
victor, fons, thanks for your replies.
Fons Adriaensen wrote:
This will show you that a simple 2nd order
lowpass will do the job - it's not a perfect
match but good enough. It's not critical at
all - for small distances you can even use
a standard shelf or parametric.
true, for this particular case it would do (and that's what i'm using
atm). but i have this idea for a plugin that takes actual mic distance,
temperature, humidity and desired distance as parameters and will do
something that is reasonably correct (not taking into account sound
diffraction or reflection at temperature boundary layers, obviously).
would be kind of cool, but i need to get a deeper understanding of the
physics involved... especially the dependance on humidity is a very
tricky and quite non-linear issue.
fons is probably right that it doesn't make all that much of a
difference, but since such a plugin could be a nice learning tool for
sound engineers, i'd want it to be as precise as reasonably possible.
google books has one interesting paper, but it's part of a rather
expensive book:
http://books.google.de/books?hl=de&lr=&id=1x_RvffW-hcC&oi=fnd&a…
there is a graph on page 307 that is quite frightening (and that's for a
constant temperature :)
i think i'll go digging in the library first.
best,
jörn
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Jörn Nettingsmeier -
victor