[sdiy] LFSR digital noise source

Tom Bugs admin at bugbrand.co.uk
Mon Nov 11 10:56:26 CET 2019

The 4015 Dual Shift Reg is a good simple chip for shift registers - just 
combine with some XOR logic (4070)
Obviously the 4006 had some useful parts making it simple to implement.

DACs can easily be implemented in hardware form - R2R network.

My Dual Digital Shift Register module went through quite a few stages of 
investigation balancing how best to implement simplicity vs complexity:

Perhaps something of a reaction to the Wiard NoiseRing which I could 
never manage to get comfortable with.

PS - Digital vs analogue noise - yes, the key from a playful perspective 
is that you can change the clock rate of the digi - great sounds!

On 11/11/2019 00:44, rsdio at audiobanshee.com wrote:
> One advantage of a CPU-based noise source is that it can be combined with a DAC for CV modulation.
> Digital noise chips typically use the single-bit output for audio. Thus, it’s like a square wave with random period but basically constant amplitude. The conversion to analog can vary the amplitude if there is a PWM effect (via capacitance).
> With a CPU and a long enough register, it’s possible to gather 8 or more bits into a word to feed a DAC. Just be sure to shift in 8 new bits for each 8-bit conversion, otherwise the values aren’t entirely independent of each other. You can easily extend this to 16-bit or even a 24-bit DAC, although using a 24-bit DAC for CV is quite dubious. LFSR hardware should be able to run at 8x, 16x, or 24x the sample rate with no problems.
> Of course, with counter logic and a stand-alone DAC chip, it’s possible to do this in pure hardware. So, I guess the CPU doesn’t really have a unique advantage here.
> Brian
> On Nov 10, 2019, at 4:32 PM, bbob <fluxmonk at gmail.com> wrote:
>> sometimes for the sound directly (crunchy/brittle), but more often slowing the clock and then using it as a modulation source
>> On Sun, Nov 10, 2019 at 7:11 PM ColinMuirDorward <colindorward at gmail.com> wrote:
>>> Hope this isn't too off topic, but I've often wondered when/why you'd choose a digital noise source over an analog one. It is simply for the acoustic flavour?
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