High Quality White Noise Gen

"Jim Slone" kirjoitti viestissä: snipped-for-privacy@news.tpg.com.au...

You can buy a CD full of white noise.

-ek

look on the Elliott Sound Products website, for pink noise gen

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You can buy noise diodes from lots of people... just google

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.

John

Racist! We want Black noise.

Then use some of Obama's speeches.

(c)Rap

Ow!

Homophobe! We want Pink noise!

John

Adobe Audition generates brown noise in addition to white and pink...

G=B2

Save the Earth. Make Green Noise.

John

A link previously mentioned in this thread offered what they said was "pink noise", along with "white noise" and "brown/red noise" IIRC.

I do get a little into a mood to test the "pink noise" to see if it is "truly pink" as opposed to something towards "purple noise"... I hope only as a result of some midrange frequency response dip in my computer loudspeakers ("they are fairly-el-cheapo" that *may* accentuate "lower treble" and "bass end of midrange").

I'm not sure what metrics you use for "best". I needed to generate some white, pink, and other cokored/filtered noises for audio testing. I used the Audacity free software program. You can generate colored noise and filter it, then save either the project or the waveform (various formats) for replay.

Does anyone know what makes a high price "noise diode" any better than your garden variety Zener?

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.)

George H.

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.

Or sum the signals from a bunch of them. Central limit theorem.

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.

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.

hen

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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.