[sdiy] Vote for your favorite noise source

[Scott Gravenhorst]

Agreed, LFSR, many stages.  I've used 24 stages, the noise
is smooth as silk, high output.  Also p-n types require selecting
transistor/diode for no "popcorn" noise, large LFSR won't popcorn.
One could argue that LFSR is not "perfect"...  I could argue that
p-n noise isn't perfect either (did I *really* get the best 
junction?).  Also, running the LFSR from a VCO allows changing
the position of the output spectrum.

Pink?  Pick you favorite filter...

Scott Bernardi <sbernardi at attbi.com> wrote:
>I've used both the pseudo random shift register type and reversed biased
>pn junctions.  The reverse biased pn junction is a much lower parts
>count, but you have to be very careful with layout and supply leads
>because it is a high gain circuit and it will amplify thumps in your
>supply lines (like from LFOs).  Also, there is some experimentation you
>have to do with the noise transistor and the amount of gain you need.
>Use multiple cascaded gain stages rather than one stage with large gain
>to preserve HF bandwidth (opamps rolloff high frequencies quite rapidly
>at high gains).
>The nice thing about pseudo random is that the level of the output is
>consistent, you can run it off your "dirty" five volt supply, and you
>don't have to worry about thumps in your supply. If you have enough
>stages there will be no detectable pattern (18 stage shift register
>repeats once every 8 minutes or so).
>
>Sound wise, they are about the same.  If I were going for "ultimate"
>noise source I'd probably use a pseudo random with white, pink, and low
>frequency random outputs.  Here's a circuit I used in my original OGEE
>synth. If I was doing it again I'd redesign it using CMOS, and use just
>a zener for the DAC reference (REF-01 is overkill, but I worked at PMI
>at the time so I had access).
>http://home.attbi.com/~sbernardi/elec/noise.html
>
>Tim Ressel wrote:
>
>> Okay boys and girls, Its time to throw caution to the
>> wind and start a new holy war:
>>
>> Part 1:
>>
>> (*)-(*)-(*)-(*)-(*)-(*)-(*)-(*)
>> Which Noise Source Is The Best?
>> (*)-(*)-(*)-(*)-(*)-(*)-(*)-(*)
>>
>> Candidates:
>>
>> Reversed-biased PN junstion (2N2712)
>> Above with constant-current source
>> Reversed-biased zener
>> Dual reversed-biased zener (MOTM??)
>> Mondo shift register with feedback
>> Small hungry infant
>> Other?
>>
>> Part 2:
>>
>> (*)-(*)-(*)-(*)-(*)-(*)-(*)-(*)
>> Which Pink Filter Is The Best ?
>> (*)-(*)-(*)-(*)-(*)-(*)-(*)-(*)
>>
>> Have fun!
>>
>> --TR
>>
>> __________________________________________________
>> Do You Yahoo!?
>> LAUNCH - Your Yahoo! Music Experience
>> http://launch.yahoo.com
>
>--
>Scott Bernardi
>sbernardi at attbi.com
>
>

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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