High Quality White Noise Gen
in [Design]
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From: John Larkin on 10 Jun 2010 22:46 On Thu, 10 Jun 2010 17:50:48 -0700 (PDT), MooseFET <kensmith(a)rahul.net> wrote: >On Jun 10, 11:49 pm, John Larkin ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> On Thu, 10 Jun 2010 07:01:03 -0700 (PDT), MooseFET >> >> >> >> <kensm...(a)rahul.net> wrote: >> >On Jun 10, 9:53 pm, John Larkin >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> >> On Thu, 10 Jun 2010 01:31:12 -0700 (PDT), MooseFET >> >> >> <kensm...(a)rahul.net> wrote: >> >> >On Jun 9, 11:15 pm, John Larkin >> >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> >> >> On Wed, 9 Jun 2010 07:32:09 -0700 (PDT), MooseFET <kensm...(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. >> >> >> >When you add asymmetric noise, the clipping rate will be greater than >> >> >when you subtract them. The effect is small but not zero. >> >> >> If you are determined to be a PITA, yes. >> >> >Sorry about the tone. I didn't sleep well last night. >> >... or perhaps yes, I am determined to be a PITA. >> >maybe with more coffee I will know which it is. >> >> >> John >> >> I've had my coffee, two cups of Peets. Snarl. Snap. > >Peet's smells rotten to me. I think they ferment it. At least it hasn't passed through rodents. http://www.paradise-coffee.com/ John
From: oopere on 11 Jun 2010 04:16 On 11 jun, 02:50, MooseFET <kensm...(a)rahul.net> wrote: > On Jun 10, 11:49 pm, John Larkin > > > > <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > > On Thu, 10 Jun 2010 07:01:03 -0700 (PDT), MooseFET > > > <kensm...(a)rahul.net> wrote: > > >On Jun 10, 9:53 pm, John Larkin > > ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > > >> On Thu, 10 Jun 2010 01:31:12 -0700 (PDT), MooseFET > > > >> <kensm...(a)rahul.net> wrote: > > >> >On Jun 9, 11:15 pm, John Larkin > > >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > > >> >> On Wed, 9 Jun 2010 07:32:09 -0700 (PDT), MooseFET <kensm...(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. > > > >> >When you add asymmetric noise, the clipping rate will be greater than > > >> >when you subtract them. The effect is small but not zero. > > > >> If you are determined to be a PITA, yes. > > > >Sorry about the tone. I didn't sleep well last night. > > >... or perhaps yes, I am determined to be a PITA. > > >maybe with more coffee I will know which it is. > > > >> John > > > I've had my coffee, two cups of Peets. Snarl. Snap. > > Peet's smells rotten to me. I think they ferment it. > > > Noise amplifiers need, well, infinite headroom, > > so we can never get it > > right. > > If the noise is to be white and not contrived, yes, > there is no way to really do it. I have had a few > cases where I needed noise that was more like a > a uniform probability over a band of values and > also a flat spectrum over a band. It can be done. > > The crappy version is just the usual white noise thing > feeding into a pair of diodes. The log like curve of > the diodes does not that bad of a job. The OP wanted white noise, not necessarily gaussian noise. Your signal may be white but just exhibit two values: Va and -Va. "White" relates to the spectral power density and "gaussian" to the probability density function. Pere PD. Our internet provider has now dropped usenet. Sorry for posting from google groups!
From: Jan Panteltje on 11 Jun 2010 06:26 On a sunny day (Fri, 11 Jun 2010 01:16:32 -0700 (PDT)) it happened oopere <oopere(a)netscape.net> wrote in <0d6af8e5-f876-458a-9ce0-50ca4eda712d(a)w12g2000yqj.googlegroups.com>: >The OP wanted white noise, not necessarily gaussian noise. Your signal >may be white but just exhibit two values: Va and -Va. "White" relates >to the spectral power density and "gaussian" to the probability >density function. > >Pere > >PD. Our internet provider has now dropped usenet. Sorry for posting >from google groups! Use news.aioe.org
From: oo pere oo on 11 Jun 2010 07:45 Jan Panteltje wrote: > On a sunny day (Fri, 11 Jun 2010 01:16:32 -0700 (PDT)) it happened oopere > <oopere(a)netscape.net> wrote in > <0d6af8e5-f876-458a-9ce0-50ca4eda712d(a)w12g2000yqj.googlegroups.com>: > >> The OP wanted white noise, not necessarily gaussian noise. Your signal >> may be white but just exhibit two values: Va and -Va. "White" relates >> to the spectral power density and "gaussian" to the probability >> density function. >> >> Pere >> >> PD. Our internet provider has now dropped usenet. Sorry for posting >>from google groups! > > Use > news.aioe.org Thanks! Now I have real news again :) Pere
From: JosephKK on 11 Jun 2010 22:09
On Fri, 11 Jun 2010 13:45:29 +0200, oo pere oo <me(a)somewhere.net> wrote: >Jan Panteltje wrote: >> On a sunny day (Fri, 11 Jun 2010 01:16:32 -0700 (PDT)) it happened oopere >> <oopere(a)netscape.net> wrote in >> <0d6af8e5-f876-458a-9ce0-50ca4eda712d(a)w12g2000yqj.googlegroups.com>: >> >>> The OP wanted white noise, not necessarily gaussian noise. Your signal >>> may be white but just exhibit two values: Va and -Va. "White" relates >>> to the spectral power density and "gaussian" to the probability >>> density function. >>> >>> Pere >>> >>> PD. Our internet provider has now dropped usenet. Sorry for posting >>>from google groups! >> >> Use >> news.aioe.org > >Thanks! Now I have real news again :) > >Pere There is also eternal-september.org. Plus a few low cost commercial providers, like where i post from. |