High Quality White Noise Gen
in [Design]
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From: John Larkin on 9 Jun 2010 10:01 On Wed, 09 Jun 2010 04:51:06 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Wed, 02 Jun 2010 10:46:33 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >> >>The math says it must be so. Still, the sum would converge to Gaussian >>faster if half of the lopsided signals were inverted. > >And that is where you tripped yourself up. Sums of lopsided signals are >still lopsided. Differences may work better. Do I now have to explain to you what the word "inverted" means? >> >>Zener noise gets more symmetric at higher currents. 10 mA is usually >>OK for a small 10-volt zener. > >Direct from the nature of the I-V curve. I don't see that. Please explain. John
From: John Larkin on 9 Jun 2010 10:03 On Wed, 09 Jun 2010 04:46:44 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Wed, 2 Jun 2010 10:37:12 -0700 (PDT), George Herold ><gherold(a)teachspin.com> wrote: > >>On Jun 2, 10:55�am, John Larkin >><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>> On Wed, 2 Jun 2010 07:32:55 -0700 (PDT), George Herold >>> >>> >>> >>> >>> >>> <gher...(a)teachspin.com> wrote: >>> >On Jun 1, 5:51�pm, John Larkin >>> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >> On Tue, 1 Jun 2010 11:35:59 -0700 (PDT), George Herold >>> >>> >> <gher...(a)teachspin.com> wrote: >>> >> >On May 31, 12:56�pm, John Larkin >>> >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >> >> On Mon, 31 May 2010 12:23:10 GMT, jimsl...(a)esterlux.com (Jim Slone) >>> >> >> wrote: >>> >>> >> >> >What are the best options for high quality audio white noise >>> >> >> >generation? >>> >>> >> >> >I have been using generic diodes and reversed biased transistors. Then >>> >> >> >someone mentioned there are special parts available with better >>> >> >> >characteristics. >>> >>> >> >> >Can anyone please give me a pointer? >>> >>> >> >> >Jim Slone >>> >>> >> >> You can buy noise diodes from lots of people... just google <noise >>> >> >> diode> >>> >>> >> >Does anyone know what makes a high price "noise diode" any better than >>> >> >your garden variety Zener? >>> >>> >> Probably a very small junction area (for low capacitance, high current >>> >> density) and maybe some doping profile. Not a power device! >>> >>> >> Regular zeners get spikey and asymmetric and sort of oscillate at low >>> >> current. You can get noise diodes that behave at low currents. >>> >>> >> >> If you want really flat, really gaussian noise, a mathematical random >>> >> >> stream (single-bit) or random word (dac) generator is probably best. >>> >> >> See AoE for details. >>> >>> >> >> For audio, it doesn't matter much. A 10-volt zener biased at a few mA >>> >> >> is fine. >>> >>> >> >Yup, and if the voltage asymmetry is a problem you can add the signal >>> >> >from two diodes, one biased from the positve supply and the other from >>> >> >the negative. �(Though I've never tried this trick.) >>> >>> >> Or sum the signals from a bunch of them. Central limit theorem. >>> >>> >Well that is not going to get rid of the voltage asymmetery. >>> >>> >If you need real Gaussian noise you can look at the shot noise from a >>> >photodiode illuminated by an LED. �Gives you noise ~100 times bigger >>> >than the johnson noise of the sense resistor. �(Assuming a 5 Volt DC >>> >drop across R). �But this has one big drawback. �It's very sensitve to >>> >vibrations. >>> >>> Shot noise is the ultimate asymmetric waveform. It's made of >>> single-photon unidirectional spikes. If it manages to be Gaussian, >>> it's because a lot of asymmetric signals are being summed. Central >>> limit theorem. >>> >>> http://en.wikipedia.org/wiki/Illustration_of_the_central_limit_theorem >>> >>> John- Hide quoted text - >>> >>> - Show quoted text - >> >>Hmmm, you are right.... I still don't think that summing the voltage >>noise from a bunch of unipolarized zeners is going to get rid of the >>voltage assymetry. But I'd be happy to be wrong too. Have you ever >>tried this? It would be simple enough to put 5 or 6 together and see >>what the output looks like. (As long as you don't mind my summing >>with an opamp)... Maybe I can find some 'fun' time on Friday. >> >>George H. > >Actually differencing them in twos, then summing seems more likely to >reduce the asymmetry. When did addition stop being associative? John
From: MooseFET on 9 Jun 2010 10:32 On Jun 9, 10:03 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Wed, 09 Jun 2010 04:46:44 -0700, > > > > "JosephKK"<quiettechb...(a)yahoo.com> wrote: > >On Wed, 2 Jun 2010 10:37:12 -0700 (PDT), George Herold > ><gher...(a)teachspin.com> wrote: > > >>On Jun 2, 10:55 am, John Larkin > >><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >>> On Wed, 2 Jun 2010 07:32:55 -0700 (PDT), George Herold > > >>> <gher...(a)teachspin.com> wrote: > >>> >On Jun 1, 5:51 pm, John Larkin > >>> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >>> >> On Tue, 1 Jun 2010 11:35:59 -0700 (PDT), George Herold > > >>> >> <gher...(a)teachspin.com> wrote: > >>> >> >On May 31, 12:56 pm, John Larkin > >>> >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >>> >> >> On Mon, 31 May 2010 12:23:10 GMT, jimsl...(a)esterlux.com (Jim Slone) > >>> >> >> wrote: > > >>> >> >> >What are the best options for high quality audio white noise > >>> >> >> >generation? > > >>> >> >> >I have been using generic diodes and reversed biased transistors. Then > >>> >> >> >someone mentioned there are special parts available with better > >>> >> >> >characteristics. > > >>> >> >> >Can anyone please give me a pointer? > > >>> >> >> >Jim Slone > > >>> >> >> You can buy noise diodes from lots of people... just google <noise > >>> >> >> diode> > > >>> >> >Does anyone know what makes a high price "noise diode" any better than > >>> >> >your garden variety Zener? > > >>> >> Probably a very small junction area (for low capacitance, high current > >>> >> density) and maybe some doping profile. Not a power device! > > >>> >> Regular zeners get spikey and asymmetric and sort of oscillate at low > >>> >> current. You can get noise diodes that behave at low currents. > > >>> >> >> If you want really flat, really gaussian noise, a mathematical random > >>> >> >> stream (single-bit) or random word (dac) generator is probably best. > >>> >> >> See AoE for details. > > >>> >> >> For audio, it doesn't matter much. A 10-volt zener biased at a few mA > >>> >> >> is fine. > > >>> >> >Yup, and if the voltage asymmetry is a problem you can add the signal > >>> >> >from two diodes, one biased from the positve supply and the other from > >>> >> >the negative. (Though I've never tried this trick.) > > >>> >> Or sum the signals from a bunch of them. Central limit theorem. > > >>> >Well that is not going to get rid of the voltage asymmetery. > > >>> >If you need real Gaussian noise you can look at the shot noise from a > >>> >photodiode illuminated by an LED. Gives you noise ~100 times bigger > >>> >than the johnson noise of the sense resistor. (Assuming a 5 Volt DC > >>> >drop across R). But this has one big drawback. It's very sensitve to > >>> >vibrations. > > >>> Shot noise is the ultimate asymmetric waveform. It's made of > >>> single-photon unidirectional spikes. If it manages to be Gaussian, > >>> it's because a lot of asymmetric signals are being summed. Central > >>> limit theorem. > > >>>http://en.wikipedia.org/wiki/Illustration_of_the_central_limit_theorem > > >>> John- Hide quoted text - > > >>> - Show quoted text - > > >>Hmmm, you are right.... I still don't think that summing the voltage > >>noise from a bunch of unipolarized zeners is going to get rid of the > >>voltage assymetry. But I'd be happy to be wrong too. Have you ever > >>tried this? It would be simple enough to put 5 or 6 together and see > >>what the output looks like. (As long as you don't mind my summing > >>with an opamp)... Maybe I can find some 'fun' time on Friday. > > >>George H. > > >Actually differencing them in twos, then summing seems more likely to > >reduce the asymmetry. > > When did addition stop being associative? Perhaps when you do it with an op-amp. (10+10)-(10+10) clips (10-10)+(10-10) doesn't That would be a whole lot of noise spiking :) > > John
From: George Herold on 9 Jun 2010 10:49 On Jun 9, 7:51 am, "JosephKK"<quiettechb...(a)yahoo.com> wrote: > On Wed, 02 Jun 2010 10:46:33 -0700, John Larkin > > > > > > <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >On Wed, 2 Jun 2010 10:37:12 -0700 (PDT), George Herold > ><gher...(a)teachspin.com> wrote: > > >>On Jun 2, 10:55 am, John Larkin > >><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >>> On Wed, 2 Jun 2010 07:32:55 -0700 (PDT), George Herold > > >>> <gher...(a)teachspin.com> wrote: > >>> >On Jun 1, 5:51 pm, John Larkin > >>> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >>> >> On Tue, 1 Jun 2010 11:35:59 -0700 (PDT), George Herold > > >>> >> <gher...(a)teachspin.com> wrote: > >>> >> >On May 31, 12:56 pm, John Larkin > >>> >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >>> >> >> On Mon, 31 May 2010 12:23:10 GMT, jimsl...(a)esterlux.com (Jim Slone) > >>> >> >> wrote: > > >>> >> >> >What are the best options for high quality audio white noise > >>> >> >> >generation? > > >>> >> >> >I have been using generic diodes and reversed biased transistors. Then > >>> >> >> >someone mentioned there are special parts available with better > >>> >> >> >characteristics. > > >>> >> >> >Can anyone please give me a pointer? > > >>> >> >> >Jim Slone > > >>> >> >> You can buy noise diodes from lots of people... just google <noise > >>> >> >> diode> > > >>> >> >Does anyone know what makes a high price "noise diode" any better than > >>> >> >your garden variety Zener? > > >>> >> Probably a very small junction area (for low capacitance, high current > >>> >> density) and maybe some doping profile. Not a power device! > > >>> >> Regular zeners get spikey and asymmetric and sort of oscillate at low > >>> >> current. You can get noise diodes that behave at low currents. > > >>> >> >> If you want really flat, really gaussian noise, a mathematical random > >>> >> >> stream (single-bit) or random word (dac) generator is probably best. > >>> >> >> See AoE for details. > > >>> >> >> For audio, it doesn't matter much. A 10-volt zener biased at a few mA > >>> >> >> is fine. > > >>> >> >Yup, and if the voltage asymmetry is a problem you can add the signal > >>> >> >from two diodes, one biased from the positve supply and the other from > >>> >> >the negative. (Though I've never tried this trick.) > > >>> >> Or sum the signals from a bunch of them. Central limit theorem. > > >>> >Well that is not going to get rid of the voltage asymmetery. > > >>> >If you need real Gaussian noise you can look at the shot noise from a > >>> >photodiode illuminated by an LED. Gives you noise ~100 times bigger > >>> >than the johnson noise of the sense resistor. (Assuming a 5 Volt DC > >>> >drop across R). But this has one big drawback. It's very sensitve to > >>> >vibrations. > > >>> Shot noise is the ultimate asymmetric waveform. It's made of > >>> single-photon unidirectional spikes. If it manages to be Gaussian, > >>> it's because a lot of asymmetric signals are being summed. Central > >>> limit theorem. > > >>>http://en.wikipedia.org/wiki/Illustration_of_the_central_limit_theorem > > >>> John- Hide quoted text - > > >>> - Show quoted text - > > >>Hmmm, you are right.... I still don't think that summing the voltage > >>noise from a bunch of unipolarized zeners is going to get rid of the > >>voltage assymetry. But I'd be happy to be wrong too. Have you ever > >>tried this? It would be simple enough to put 5 or 6 together and see > >>what the output looks like. (As long as you don't mind my summing > >>with an opamp)... Maybe I can find some 'fun' time on Friday. > > >>George H. > > >The math says it must be so. Still, the sum would converge to Gaussian > >faster if half of the lopsided signals were inverted. > > And that is where you tripped yourself up. Sums of lopsided signals are > still lopsided. Differences may work better. Differences will work better, but simple adding works too! The sum may still be lopsided, but less lopsided than the input. It's the Gaussian nature of shot noise (very asymmetric if you could look fast enough.) that made me reassess my previous misconception. (As a recent convert to the central limit theorem Im perhaps more ardent than those with long held belief.) George H. > > > > >Zener noise gets more symmetric at higher currents. 10 mA is usually > >OK for a small 10-volt zener. > > Direct from the nature of the I-V curve. > > > > > > >I sometimes generate Gaussian-distributed numbers by summing a bunch > >of RAN() calls, which are uniform on [0,1]. Six to ten works well, and > >the crest factor is finite and known. > > >John- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text -
From: John Larkin on 9 Jun 2010 11:15
On Wed, 9 Jun 2010 07:32:09 -0700 (PDT), MooseFET <kensmith(a)rahul.net> wrote: >On Jun 9, 10:03 pm, John Larkin ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> On Wed, 09 Jun 2010 04:46:44 -0700, >> >> >> >> "JosephKK"<quiettechb...(a)yahoo.com> wrote: >> >On Wed, 2 Jun 2010 10:37:12 -0700 (PDT), George Herold >> ><gher...(a)teachspin.com> wrote: >> >> >>On Jun 2, 10:55 am, John Larkin >> >><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>> On Wed, 2 Jun 2010 07:32:55 -0700 (PDT), George Herold >> >> >>> <gher...(a)teachspin.com> wrote: >> >>> >On Jun 1, 5:51 pm, John Larkin >> >>> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>> >> On Tue, 1 Jun 2010 11:35:59 -0700 (PDT), George Herold >> >> >>> >> <gher...(a)teachspin.com> wrote: >> >>> >> >On May 31, 12:56 pm, John Larkin >> >>> >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>> >> >> On Mon, 31 May 2010 12:23:10 GMT, jimsl...(a)esterlux.com (Jim Slone) >> >>> >> >> wrote: >> >> >>> >> >> >What are the best options for high quality audio white noise >> >>> >> >> >generation? >> >> >>> >> >> >I have been using generic diodes and reversed biased transistors. Then >> >>> >> >> >someone mentioned there are special parts available with better >> >>> >> >> >characteristics. >> >> >>> >> >> >Can anyone please give me a pointer? >> >> >>> >> >> >Jim Slone >> >> >>> >> >> You can buy noise diodes from lots of people... just google <noise >> >>> >> >> diode> >> >> >>> >> >Does anyone know what makes a high price "noise diode" any better than >> >>> >> >your garden variety Zener? >> >> >>> >> Probably a very small junction area (for low capacitance, high current >> >>> >> density) and maybe some doping profile. Not a power device! >> >> >>> >> Regular zeners get spikey and asymmetric and sort of oscillate at low >> >>> >> current. You can get noise diodes that behave at low currents. >> >> >>> >> >> If you want really flat, really gaussian noise, a mathematical random >> >>> >> >> stream (single-bit) or random word (dac) generator is probably best. >> >>> >> >> See AoE for details. >> >> >>> >> >> For audio, it doesn't matter much. A 10-volt zener biased at a few mA >> >>> >> >> is fine. >> >> >>> >> >Yup, and if the voltage asymmetry is a problem you can add the signal >> >>> >> >from two diodes, one biased from the positve supply and the other from >> >>> >> >the negative. (Though I've never tried this trick.) >> >> >>> >> Or sum the signals from a bunch of them. Central limit theorem. >> >> >>> >Well that is not going to get rid of the voltage asymmetery. >> >> >>> >If you need real Gaussian noise you can look at the shot noise from a >> >>> >photodiode illuminated by an LED. Gives you noise ~100 times bigger >> >>> >than the johnson noise of the sense resistor. (Assuming a 5 Volt DC >> >>> >drop across R). But this has one big drawback. It's very sensitve to >> >>> >vibrations. >> >> >>> Shot noise is the ultimate asymmetric waveform. It's made of >> >>> single-photon unidirectional spikes. If it manages to be Gaussian, >> >>> it's because a lot of asymmetric signals are being summed. Central >> >>> limit theorem. >> >> >>>http://en.wikipedia.org/wiki/Illustration_of_the_central_limit_theorem >> >> >>> John- Hide quoted text - >> >> >>> - Show quoted text - >> >> >>Hmmm, you are right.... I still don't think that summing the voltage >> >>noise from a bunch of unipolarized zeners is going to get rid of the >> >>voltage assymetry. But I'd be happy to be wrong too. Have you ever >> >>tried this? It would be simple enough to put 5 or 6 together and see >> >>what the output looks like. (As long as you don't mind my summing >> >>with an opamp)... Maybe I can find some 'fun' time on Friday. >> >> >>George H. >> >> >Actually differencing them in twos, then summing seems more likely to >> >reduce the asymmetry. >> >> When did addition stop being associative? > >Perhaps when you do it with an op-amp. > >(10+10)-(10+10) clips > >(10-10)+(10-10) doesn't > >That would be a whole lot of noise spiking :) > The signals (zener noise) are mildly asymmetric noise, not DC values. When you add noise, it doesn't matter what order you add or subtract them in. And besides, a true Gaussian distribution has probability tails to infinity; the opamps have to clip once in a while. A rational designer would just makes sure it doesn't happen often. [1] JKK is so eager to be right, and for others to be wrong, he makes a lot of stupid statements. He's not the only one. Allow me to pass on what Miss Denton taught me in 6th grade: Check your work. John [1] summing computer-generated random numbers results in a distribution with finite peaks, basically Gaussians with their tails clipped. That can be handy. |