High Quality White Noise Gen
in [Design]
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From: George Herold on 1 Jun 2010 14:35 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? > > 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.) > > John George H.
From: John Larkin on 1 Jun 2010 17:51 On Tue, 1 Jun 2010 11:35:59 -0700 (PDT), George Herold <gherold(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. John
From: Robert Baer on 2 Jun 2010 01:57 John Larkin wrote: > On Mon, 31 May 2010 21:48:40 -0700 (PDT), Glenn Gundlach > <stratus46(a)yahoo.com> wrote: > >> On May 31, 7:21 pm, John Larkin >> <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>> On Mon, 31 May 2010 15:44:06 -0700, Robert Baer >>> >>> <robertb...(a)localnet.com> wrote: >>>> 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 >>>> Racist! >>>> We want Black noise. >>> Homophobe! We want Pink noise! >>> >>> John >> Adobe Audition generates brown noise in addition to white and pink... >> >> G� > > Save the Earth. Make Green Noise. > > John > Just "made" a rather noisy generator: reversed biased E-B junction of a 2N3439 (the first metal case transistor pulled out of an old junkbox) in series with a DN3545 which uses a 33K resistor to make an 80uA current source. Using 20-30V, the noise is over 1V peak to peak, sawtooth looking with some ringing at the start of the positive going ramp. E-B breakdown was about 15V.
From: George Herold on 2 Jun 2010 10:32 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. George H. > > John- Hide quoted text - > > - Show quoted text -
From: George Herold on 2 Jun 2010 10:36
On Jun 2, 1:57 am, Robert Baer <robertb...(a)localnet.com> wrote: > John Larkin wrote: > > On Mon, 31 May 2010 21:48:40 -0700 (PDT), Glenn Gundlach > > <stratu...(a)yahoo.com> wrote: > > >> On May 31, 7:21 pm, John Larkin > >> <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >>> On Mon, 31 May 2010 15:44:06 -0700, Robert Baer > > >>> <robertb...(a)localnet.com> wrote: > >>>> 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 > >>>> Racist! > >>>> We want Black noise. > >>> Homophobe! We want Pink noise! > > >>> John > >> Adobe Audition generates brown noise in addition to white and pink... > > >> G² > > > Save the Earth. Make Green Noise. > > > John > > Just "made" a rather noisy generator: reversed biased E-B junction of > a 2N3439 (the first metal case transistor pulled out of an old junkbox) > in series with a DN3545 which uses a 33K resistor to make an 80uA > current source. > Using 20-30V, the noise is over 1V peak to peak, sawtooth looking > with some ringing at the start of the positive going ramp. > E-B breakdown was about 15V.- Hide quoted text - > > - Show quoted text - Oh, I never heard of that. Is it avalanche breakdown of the E-B junction. Does this give noise out to a higher frequency than a 15V zener? George H. |