True RMS meter
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Re: True RMS meter
by superbigio
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Thanks Greg,
is there a particular reason that you use a 2nd order LPF when it could be done with a 1st order ? - Luigi --- Greg Berchin <gberchin@...> wrote: > On Tue, 26 Jun 2007 06:08:56 -0400 (EDT), Luigi Castelli wrote: > > >1 - With Average detection I intend to simulate VU-like metering. > >According to the specs a VU meter is defined to reach 99% full-scale > >deflection in 300ms. Its fall-back time is also the same of its rise > >time. > > VU ballistics assume mechanical meters, easily modeled with a second > order system: > > > > Greg Berchin > > -- > dupswapdrop -- the music-dsp mailing list and website: > subscription info, FAQ, source code archive, list archive, book > reviews, dsp links > http://music.columbia.edu/cmc/music-dsp > http://music.columbia.edu/mailman/listinfo/music-dsp > ------------------------------------------------------------ THIS E-MAIL MESSAGE IS FOR THE SOLE USE OF THE INTENDED RECIPIENT AND MAY CONTAIN CONFIDENTIAL AND/OR PRIVILEGED INFORMATION. ANY UNAUTHORIZED REVIEW, USE, DISCLOSURE OR DISTRIBUTION IS PROHIBITED. IF YOU ARE NOT THE INTENDED RECIPIENT, CONTACT THE SENDER BY E-MAIL AT SUPERBIGIO@... AND DESTROY ALL COPIES OF THE ORIGINAL MESSAGE. WITHOUT PREJUDICE UCC1-207. ------------------------------------------------------------ ____________________________________________________________________________________ Looking for earth-friendly autos? Browse Top Cars by "Green Rating" at Yahoo! Autos' Green Center. http://autos.yahoo.com/green_center/ -- dupswapdrop -- the music-dsp mailing list and website: subscription info, FAQ, source code archive, list archive, book reviews, dsp links http://music.columbia.edu/cmc/music-dsp http://music.columbia.edu/mailman/listinfo/music-dsp |
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Re: True RMS meter
by Peter Schoffhauzer
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Luigi Castelli wrote:
> Thanks Greg, > > is there a particular reason that you use a 2nd order LPF when it could > be done with a 1st order ? I think he uses a 2nd order filter because the specification defines the minimum overshoot (ringing) of the system to be between 1-1.5%, and first order systems don't have ringing. Quote from http://sound.westhost.com/project55.htm: "VU: A VU meter is designed to have a relatively slow response. It is driven from a full-wave averaging circuit defined to reach 99% full-scale deflection in 300ms and overshoot not less than 1% and not more than 1.5%." -- Peter -- dupswapdrop -- the music-dsp mailing list and website: subscription info, FAQ, source code archive, list archive, book reviews, dsp links http://music.columbia.edu/cmc/music-dsp http://music.columbia.edu/mailman/listinfo/music-dsp |
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Re: True RMS meter
by Hans Fugal-3
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Once upon a time, Greg Berchin wrote:
> On Tue, 26 Jun 2007 06:08:56 -0400 (EDT), Luigi Castelli wrote: > >> 1 - With Average detection I intend to simulate VU-like metering. >> According to the specs a VU meter is defined to reach 99% full-scale >> deflection in 300ms. Its fall-back time is also the same of its rise >> time. > > VU ballistics assume mechanical meters, easily modeled with a second > order system: > > http://groups.google.com/group/comp.dsp/tree/browse_frm/thread/260b526f35efe34f/cc5b9afb71b4752f?rnum=1&_done=%2Fgroup%2Fcomp.dsp%2Fbrowse_frm%2Fthread%2F260b526f35efe34f%2Fcc5b9afb71b4752f%3Ftvc%3D1%26#doc_dbf323f74b343be6 > I've been trying to figure out how to implement this but I'm finding my dsp-fu is weak, and I'm traveling and my dsp text is several states away. So forgive me for asking a perhaps rudimentary question. How does one get from "2nd-order LPF set for 2.224 Hz, Q = 0.6053" to a transfer equation for a digital filter (or even better, a difference equation)? -- Hans Fugal ; http://hans.fugal.net There's nothing remarkable about it. All one has to do is hit the right keys at the right time and the instrument plays itself. -- Johann Sebastian Bach -- dupswapdrop -- the music-dsp mailing list and website: subscription info, FAQ, source code archive, list archive, book reviews, dsp links http://music.columbia.edu/cmc/music-dsp http://music.columbia.edu/mailman/listinfo/music-dsp |
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Re: True RMS meter
by david.lowenfels
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Hi Hans,
Try RBJ's filter cookbook: http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt -D On Jul 8, 2008, at 12:01 PM, Hans Fugal wrote: > > I've been trying to figure out how to implement this but I'm finding > my dsp-fu is weak, and I'm traveling and my dsp text is several > states away. So forgive me for asking a perhaps rudimentary question. > > How does one get from "2nd-order LPF set for 2.224 Hz, Q = 0.6053" > to a transfer equation for a digital filter (or even better, a > difference equation)? > > -- > Hans Fugal ; http://hans.fugal.net -- dupswapdrop -- the music-dsp mailing list and website: subscription info, FAQ, source code archive, list archive, book reviews, dsp links http://music.columbia.edu/cmc/music-dsp http://music.columbia.edu/mailman/listinfo/music-dsp |
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Re: True RMS meter
by Nigel Redmon
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On Jul 8, 2008, at 12:01 PM, Hans Fugal wrote:
> How does one get from "2nd-order LPF set for 2.224 Hz, Q = 0.6053" > to a transfer equation for a digital filter (or even better, a > difference equation)? Here's another look, including the bilinear transform--skip to the bottom for the coefficient equations for a 2nd-order LFP: http://www.earlevel.com/Digital%20Audio/Bilinear.html Here's are some notes on implementing biquads: http://www.earlevel.com/Digital%20Audio/Biquads.html You didn't mention how you're implementing this--a fixed-point DSP, floating point CPU, etc. Your frequency requirement is pretty low (assuming audio sample rates), and the standard biquad configurations are pretty sensitive to quantization effects for low frequencies. The second link also has some notes on this topic. -- dupswapdrop -- the music-dsp mailing list and website: subscription info, FAQ, source code archive, list archive, book reviews, dsp links http://music.columbia.edu/cmc/music-dsp http://music.columbia.edu/mailman/listinfo/music-dsp |
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