Re: [Audacity-devel] waveform dB use
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Re: [Audacity-devel] waveform dB use
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From: Martyn S. <mar...@gm...> - 2015-09-01 00:44:19
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Hmm Balloon pops are good for down to low frequencies in my trials, but speakers can be limited. For the other methods both mike and speaker have to be good. It's all about compromises. Convolving a 'pop' with a quite recording does a reasonable job with the Aurora plug-ins. TTFN Martyn On 27/08/2015 05:56, Federico Miyara wrote: > > Paul, > > While the balloon method may be accurate enough to find the decay > curves of a room at different frequencies, the balloon pop is not an > accurate representation of an impulse, so the recorded signal is not a > good simulation of the room's impulse response. Methods used to > measure the impulse response range from MLS sequences (maximum length > sequences, sort of irregular square wave which in the long run has an > almost flat spectrum) to frequency sweeps. In all cases a > transformation is necessary to collapse the time-spread information > into an impulse response. > > There is a plugin set by the italian researcher Angelo Farina called > Aurora that allows several of these algorithms. > > Regards, > > Federico > > > On 26/08/2015 23:12, Paul Licameli wrote: >> I wonder, what if you convolved any sound with that pop? Would that >> simulate that room's reverb? It could be easy to do with Nyquist. >> >> PRL >> >> >> On Wed, Aug 26, 2015 at 9:20 PM, Martyn Shaw <mar...@gm... >> <mailto:mar...@gm...>> wrote: >> >> I have been doing the same with balloons. They are cheap and you >> don't need a speaker (with it's limited LF response), just a decent >> mike (which you need with the other method anyway). I have >> concluded >> that the balloon method is best for me. >> >> TTFN >> Martyn >> >> On 26/08/2015 19:28, Gary Nelson wrote: >> > FWIW, >> > I use Waveform dB to estimate reverberation time of a room. >> Start a >> > recording, pop a large well inflated balloon to approximate an >> > impulse. Exponential decay shows as wedge you >> mentioned--linear decay >> > on dB log scale. Measure decay time for 20 or 40 or, >> ideally, 60dB. >> > In any event, measure or extrapolate time for 60dB attenuation >> to get >> > RT60 (ReverbTime to -60dB). >> > Or >> > Make a track with white noise. Play it and simultaneously record. >> > Decay starts when noise burst ends. Same as above. >> > >> > Not a likely candidate for frequent use, but useful. Maybe an >> app note >> > would be useful. >> > >> > >> > >> > GN >> > >> > >> > >> > >> > Sent from my iPad >> > >> > "There is nothing which can better deserve our patronage >> than the >> > promotion of science and literature. Knowledge is in every >> country >> > the surest basis of public happiness." >> > >> > - George Washington, address to Congress (1790) >> > >> > On Aug 19, 2015, at 10:28 AM, Paul Licameli >> <<mailto:pau...@gm...>pau...@gm... >> > <mailto:<mailto:pau...@gm...>pau...@gm...>> wrote: >> > >> >> >> >> >> >> On Wed, Aug 19, 2015 at 1:15 PM, Steve the Fiddle >> >> <ste...@gm... <mailto:ste...@gm...> >> <mailto:ste...@gm... >> <mailto:ste...@gm...>>> wrote: >> >> >> >> On 19 August 2015 at 17:16, Alan Horstmann >> >> <gi...@as... <mailto:gi...@as...> >> <mailto:gi...@as... >> <mailto:gi...@as...>>> wrote: >> >> > On Wednesday 19 August 2015 12:54, Steve the Fiddle wrote: >> >> > >> >> > <snip> >> >> > >> >> >> On the subject of track scales, one feature (bug) that >> I would very >> >> >> much like to see improved if anyone can work out how >> to do it (Paul?), >> >> >> is for the dB ruler to extend down into the negative >> part of the >> >> >> waveform. >> >> > >> >> > You mean in Waveform (dB)? I think I could fairly >> easily argue that the >> >> > negative part of the waveform is the bug in a dB view - >> dB is a measure of >> >> > power, rms. That's what has always seemed wrong to >> me. And what is below >> >> > -infinity? (Probably +infinity!) :)) >> >> >> >> Yes I mean the track display formerly known as "Waveform >> (dB)". >> >> >> >> You are correct that this is not a "true" logarithmic >> scaling, >> >> but it >> >> is a very common way to display waveforms in audio >> applications, and >> >> for many users is the preferred display style. >> >> >> >> What the display actually shows is a logarithmically >> scaled waveform >> >> for positively going peaks in the upper half of the >> display, and an >> >> "inverted (logarithmically scaled (inverted waveform))" for >> >> negatively >> >> going peaks. >> >> >> >> In other words, negative going peaks are inverted, then >> the log of >> >> each (positive) sample value it taken, which is then >> multiplied >> >> by -1. >> >> The result of which is to produce a logarithmically >> scaled view >> >> which >> >> retains information about whether the peak is positively >> going or >> >> negatively going. >> >> >> >> The appropriate vertical ruler for this would: >> >> * Upper half of waveform: >> >> 0 dB at top of scale down to -Min dB at the bottom >> (centre line). >> >> >> >> * Lower half of the waveform: >> >> -Min dB at the top (centre line), 0 dB at the bottom. >> >> >> >> (because we don't have an infinite amount of screen space, we >> >> don't go >> >> to "-infinity dB" but have a minimum level set in >> Preferences, >> >> which I >> >> refer to here as "-Min dB") >> >> >> >> Steve >> >> >> >> >> >> >> >> Good description. >> >> >> >> The ideal logarithmic transformation of linear waveform view to >> >> logarithmic really makes the upper half stretch semi-infinitely >> >> downward and likewise the lower half stretches up, and >> practically >> >> we must elide those infinities at some arbitrary place, which is >> >> -60dB by default but changeable formerly in Interface preferences >> >> but now also by ctrl-mousewheel in the vertical ruler. >> >> >> >> If you Amplify a sound by 1 dB and then ctrl-r repeatedly, and >> >> observe Waveform dB closely, you see the positive part shift up >> >> without change of shape and the negative part shift down. I >> think >> >> of it as unrolling those two infinite scrolls that touch in >> the middle. >> >> >> >> If you have a percussive sound with a natural exponentially >> decaying >> >> envelope (or use the Pluck generator which simulates that), then >> >> Waveform dB view makes the decaying sound look like a wedge with >> >> straight sides. >> >> >> >> PRL >> >> >> >> >> >> > >> >> > Regards >> >> > >> >> > Alan >> >> > >> >> > >> >> >> ------------------------------------------------------------------------------ >> >> > _______________________________________________ >> >> > audacity-devel mailing list >> >> > aud...@li... >> <mailto:aud...@li...> >> >> <mailto:aud...@li... >> <mailto:aud...@li...>> >> >> >https://lists.sourceforge.net/lists/listinfo/audacity-devel >> >> >> >> >> ------------------------------------------------------------------------------ >> >> _______________________________________________ >> >> audacity-devel mailing list >> >> aud...@li... >> <mailto:aud...@li...> >> >> <mailto:aud...@li... >> <mailto:aud...@li...>> >> >>https://lists.sourceforge.net/lists/listinfo/audacity-devel >> >> >> >> >> >> >> ------------------------------------------------------------------------------ >> >> _______________________________________________ >> >> audacity-devel mailing list >> >> aud...@li... >> <mailto:aud...@li...> >> >> <mailto:aud...@li... >> <mailto:aud...@li...>> >> >> https://lists.sourceforge.net/lists/listinfo/audacity-devel >> > >> > >> > >> ------------------------------------------------------------------------------ >> > >> > >> > >> > _______________________________________________ >> > audacity-devel mailing list >> > aud...@li... >> <mailto:aud...@li...> >> > https://lists.sourceforge.net/lists/listinfo/audacity-devel >> > >> >> ------------------------------------------------------------------------------ >> _______________________________________________ >> audacity-devel mailing list >> aud...@li... >> <mailto:aud...@li...> >> https://lists.sourceforge.net/lists/listinfo/audacity-devel >> >> >> >> >> ------------------------------------------------------------------------------ >> >> >> _______________________________________________ >> audacity-devel mailing list >> aud...@li... >> https://lists.sourceforge.net/lists/listinfo/audacity-devel > > > > ------------------------------------------------------------------------------ > > > > _______________________________________________ > audacity-devel mailing list > aud...@li... > https://lists.sourceforge.net/lists/listinfo/audacity-devel > |